Primitive Archer
Main Discussion Area => Bows => Topic started by: Badger on April 12, 2018, 11:44:00 am
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Tim is having problems with the registration process so asked me to post for him until he gets the problem resolved.
Experimenting With Sinew.
Sinew is useful for keeping short bows from breaking, but is not good at increasing the cast of mid-length and longer wooden bows. This is largely because sinew is lightly strained in such situations, and has high mass.
The idea here is to cause the sinew to be far more strained than typically, making it do far more work per mass. Elevating the sinew well above the bow back would accomplish this by increasing it's percentage of stretch.
This first experiment elevated the sinew by placing a filler of hide glue-soaked cotton string between the back and the sinew. The goal was to see to what degree draw weight could be increased while raising mass by small amounts.
The belly is bamboo, 46" long, weighing 5.5 ounces.
The dry weight of the sinew and glue is about 2 ounces.
Once in place the bow was twice as thick as the bamboo alone.
The bow was held in 5" of reflex when sinewed, holding 6" of just-unbraced reflex.
Draw weight rose 400% of that of the bamboo alone!
Some touch-up tillering is needed, so corrective amounts of sinew will be added in a couple of areas before going to full draw, and a visit to the chronograph. My guess it that it will well outshoot same-draw weight conventionally sinewed wooden bows, and Asiatic composites. We'll see.
Meanwhile, please let me know of other efforts to get more work out of sinew by elevating it above the bow back. And your results, and details, if you do something along these lines yourself.
Arguments, comments and suggestions welcomed.
Tim Baker
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I like the idea of raising the sinew but I'm wondering if the hide glue soaked cotton is heavier than wood. Maybe a layer of some light wood would accomplish the same thing with a little bit less mass gain?
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This has already been done with a light crowned core. Really it's just a composite of simpler materials but the principle is the same.
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This has already been done with a light crowned core.
Pat, do you have any more details about the arrangement of core and sinew in that example? Or know what the core was constructed from? It seems to me that if the sinew is going to stretch or work very much, that the core has to be able to withstand almost the same amount of stretching as the sinew, or core will fail under the sinew. This rules out any woods that I know of.
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The core remains intact generally in composites with tips touching reflex and long draws.
To use sinew effectively in mid to longer bows you just limit it to hard working sections and make sure the bow is drawn farther.
Seems like Tim has brought up the old solution in search of a problem. This topic came up on here about 15 years ago. Not sure why Tim is bumping it again?
The weight of the glue soaked cotton needs to be factored in as well. It won't get a free ride.
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Tim Baker says
DC: Yes, light wood will be better. The cotton/glue just reduced the mount of sinew needed.
PatM: Can you point me to details on the version you mentioned: the % of sinew to total bow mass, the height of the sinew above the NP, draw weight increase,etc. Any idea where I can find the mentioned 15-year old related posting?
This version elevated the sinew enough to double the thickness of the bow, used about 2 ounces of sinew, compared to the bamboo's 5.5 ounces The fact that draw weight rose by 400% with a relatively small mass increase is what's encouraging so far.
Tim
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thank you for posting, great to have the chance to hear your ideas,, great to have you here, B
and thank you Badger :)
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Maybe one of the mods could look at Tims Account. it says he is logged in but when he goes to post it puts him back through the registration process.
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Interesting post.Glad to see Tim running some projects by he's been fooling with.Thanks Steve for posting it.I've fooled with borderline projects like this.Crowned sinew with lots of reflex/on working portion of limbs/light weight outer limbs.Just on 60" & 58" bows though.They do shoot outstanding.I would think with shorter less mass weighing limbs not quite as much reflex should be needed with the same or more result depending on poundage also.
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"PatM: Can you point me to details on the version you mentioned: the % of sinew to total bow mass, the height of the sinew above the NP, draw weight increase,etc. Any idea where I can find the mentioned 15-year old related posting?"
Pretty sure the old posts are long gone. The idea back then was pretty identical.
Not sure of the actual masses of things and draw weight bumping since I don't weight the stuff or bend things much before assembly.
The basic idea is a wood backing strip shaped so that the center is a higher ridge and the sinew sits mostly on that. Basically like the Kasan ridge of a Turkish bow but running up the limb more.
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Tim and Steve,
Enjoying this as a new post, wasn't here 15 years ago...I thought of flax linen+sinew...Is there a reason Tim used cotton...What does this do to the neutral plane with the cotton layer...Does this also take some compression stress off the belly...
Thanks, Don
Combed flax would be a better choice yet.
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Tim Baker says:
Burchett--Don:
" Is there a reason Tim used cotton...What does this do to the neutral plane with the cotton layer...Does this also take some compression stress off the belly..."
It's only job was elevating the sinew, to judge the effect The bamboo was 50% of finished thickness, the cotton/glue about 25%, the sinew the top 25%. Chose the cotton assuming it would be fairly neutral in tension and compression, not throwing off measurement of the elevated sinew's performance by any large degree. Another reason for using cotton was to prevent having to make a perfectly smooth surface on the bamboo, as when preparing a surface for wood core.
PatM:
Yes, similar idea. Sinew on a higher ridge would work harder. This highest, hardest working portion would have a small cross section, not raising draw weight substantially. To raise draw weight/energy storage by several times requires a lot of sinew, placed way above the NP, and as close to rectangular as feasible, making all of the sinew work equally hard.
Tim
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Maybe one of the mods could look at Tims Account. it says he is logged in but when he goes to post it puts him back through the registration process.
Steve
He is just having to do what every other new members has to do. Once he post 3 or 4 times the questions will stop
As to his "idea". Why use cotton? Just mound the sinew in a high crown down the center of the limb, that is what I always did.
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Has anyone ever had sinew break in tension? How about without breaking the bow? I'm thinking about a little sinew spaced away from the belly versus a lot of sinew closer to the belly.
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Tim,
Exploring new ideas about energy storage on the tension side seems worthwhile.
Don, you are from yew country, is there something special about yew sapwood?
Seems like it's a necessary part of the thicker than usual bows, possibly a good candidate for a core in the rectangular design?
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Hmmm? Cool idea to get the sinew working a little more. Seems to me a wider flat sinew back would work better than just a crown when the arrow is released. More working area. One thing I have found with sinew tension in horn/sinew bows 50/50 ratio. After 6 months of seasoning the bow will have 13" of reflex or so from sinew curing. Using heat on the horn to reduce that reflex to 7" or so to make it more stable does not seem to change the early draw weight much. Like the sinew with the decreased reflex is just constantly already strained even with the bow unstrung. Horn is about the heaviest thing you can make a bow out of though so it will never be the fastest. Just need to find something like it that weighs a fraction of it. Use your same ratio 50/25/25. Back "X" with sinew until it cures to a large reflex and do the Perry reflex to attach it to the wood.
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BowEd:
When sinew is placed that far above the NP it's made to stretch several %, but flax can only stretch 1 %, so it would break before a reflexed bow was braced. It also doesn't spring back well when stretched so can't return much stored energy. Likely why they never used flax on Asiatic composites.
Marc:
" Just mound the sinew in a high crown down the center of the limb..." That works to some extent, but since most of the mass of the sinew is then much lower than the top of the crown it's doing far less work yet adding considerable mass. The crown top is also a relatively small amount of sinew so can't store the needed energy for high draw weight increase. The geometry used here raised draw weight not by just the typical few % points but by several times. Less than half the mass increase bought four times the draw weight. -- Tim
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Mark:
Thanks for the posting clue.
DC:
" ... I'm thinking about a little sinew spaced away from the belly versus a lot of sinew closer to the belly."
Yes, a little sinew spaced away from the belly would make it stretch more and store more energy per mass. That's the base idea here, just enlarged a bit: A little sinew can only store a little energy, raising draw weight just a little, so put a lot of sinew spaced away from the belly and store a lot of energy. The 2 ounces of elevated sinew in this test bow caused it to store 4 times the energy of the 5.5 ounce bow alone.
Tim
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Aren't you mostly just seeing the effect of increased thickness of the bow? Twice as wide is twice as strong, twice as thick is 8 times as strong.
What is the thickness measurement of the final stack of material? We've all glued two pretty flimsy feeling pieces of Ipe and Bamboo together and had a railroad tie when the glue sets.
I always use the sinew backed strip of wood glued up separately in extreme reflex and then glue that down to my belly material now for several reasons. I think that's what Chuck was suggesting.
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BowEd:
When sinew is placed that far above the NP it's made to stretch several %, but flax can only stretch 1 %, so it would break before a reflexed bow was braced. It also doesn't spring back well when stretched so can't return much stored energy. Likely why they never used flax on Asiatic composites.
I see your point.I was concentrating too much about the mass weight factor I suppose.Never seen cotton used on the Asiatics either though and would think cotton has a breaking point too.Cotton has no spring back properties either I would think.
The difference of the distance of raised sinew on the back and difference of mass weight by replacement with cotton to all sinew would be interesting to see.2 bows the exact same length/width/and thickness made would reveal the difference.
One of the concerns too I would have is the core staying in robust good working shape to keep that high energy storage.
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Cotton is more elastic than hemp of flax but I'm pretty sure its density is as high or even higher than theirs. That would still make it heavier than wood when saturated with glue.
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Cotton is more elastic than hemp of flax but I'm pretty sure its density is as high or even higher than theirs. That would still make it heavier than wood when saturated with glue.
Maybe a strip of Balsa instead?
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I think you'd still need a bit more "fiber" to the ridged portion. Even typical core woods are about half the mass of cotton or other plant fibers.
I would dabble with something like willow or alder before Balsa..
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Don, you are from yew country, is there something special about yew sapwood?
I don't have a lot of experience with other woods. Let's just say that it wouldn't surprise me if Yew sapwood stretched a bit more than average.
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How is this different from a cable bow with the sinew being twisted as the Eskimos did? Jawge
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interesting question George. considering that sinew is supposed to stretch much more than wood, you would think that the Eskimo bows would use some sort of fret or trestle to elevate the sinew cord off the back, yet many examples did not. I don't know much about the qualities of whale sinew, however
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I like this udea and think a cooked bamboo belly with a cork core, make one of my short bows i like, tlsinewed, would be fun. Gonna start this weekend.
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Has anyone ever had sinew break in tension? How about without breaking the bow? I'm thinking about a little sinew spaced away from the belly versus a lot of sinew closer to the belly.
Sinew can stretch like 5% whereas wood can only stretch about 1%. If he had a bow that broke the sinew you would be getting some out of this world bends. It's possible that it breaks when the wood breaks underneath it because then that sinew is subject to all that force and stretches it beyond that 5%, but it's not because of the bend that it broke.
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How is this different from a cable bow with the sinew being twisted as the Eskimos did? Jawge
I was wondering the same thing. Tim, didn't you do a silk cable bow with raised nodes from bamboo? Why not go that direction some more, or were you looking to also gain the protective layer that helps keep fibers down too?
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Do you think cork will stand the shear forces? I can see it ripping apart.
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It will be fun to see if it cant. But with the compression force of sinew pressing down on the cork as the bow bends, and the sponge like structure of cork. Id bet it will hold fine.
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I think pure cork, not the shreeded processed stuff it what is needed.
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Thanks for posting this thread I spent most of my work day thinking about your design it really passed the time , but the thoughts in the end were, wouldn't you gain the same performance increase by increasing the reflex & stratigicly placing & crowning the sinew like Marc did in his 64 in. Maple recurve a while back ? Or a combination of light lams in the mix increasing limb thickness ? If the goal is to max the sinew tension with out mass gain it seems the above would accomplish that also ? Well I had 500 Mi. To think on it , Just my thoughts I'm not saying that defenitivly I'm just asking ?
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PatM:
Sinew is much less stiff than wood and stretches several time farther, so making bow thickness double by using sinew instead of wood raises draw weight by about 4 times instead of 8, and does so safely, where wood would break.
Yes, glue-soaked cotton is as heavy or heavier than bow wood. It's likely not the perfect elevator. one of it's purposes was to save sinew. Elevating the sinew was the goal, and being essentially neutral in tension or compression, it did that without the complications a wood core would bring--using a wood core would be essentially the same as starting with a thicker bow.
Mark:
Yes, balsa, or similar, might be better. Sheer forces develop in the limb; if back and belly can slip and relieve the strain it seems this would create large hysteresis and reduce stored energy [more study needed], if so then the trick will be to find a material stiff enough to resist slippage/deformation but be as light as possible.
I recently whipped some hide glue into a foamy froth; when it dried it was about .10 specific gravity and quite rigid. Some versions of that might be the ideal elevator. Experiments needed.
George:
The sinew on Inuit cable bows and similar was not highly elevated and not of large enough diameter to raise draw weight as in this case. And possibly the sheer-slippage situation too. Their ingenuity went simply into getting a working bow at all, from no apparent makings. If they'd had decent wood they likely would't have bothered with sinew.
gfugal:
Yes, once made silk cable-backed bows, the cable elevated with the nodes. A couple of problems with that: Since the cable is uniform in diameter it stretches most near the grip, essentially dead weight at the outer limb. This also meant that energy was mostly stored in the near grip sinew.
DC: Cork and related is well worth trying. It might surrender to the sheer forces, but only one way to know.
Stick bender:
Crowning the sinew means that only the top of the crown is highly stressed, sinew below that having progressively more mass per work done. And the hardest working crown-top portion would be a relatively small amount of sinew, unable to store near the energy of a rectangular section of equally high sinew. Typically such designs only gain a few extra pounds over the wood itself, the maid point of the sinew being to keep the bow from breaking.
But this is all in-progress thinking.
Tim
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"Crowning the sinew means that only the top of the crown is highly stressed, sinew below that having progressively more mass per work done. And the hardest working crown-top portion would be a relatively small amount of sinew, unable to store near the energy of a rectangular section of equally high sinew. Typically such designs only gain a few extra pounds over the wood itself, the maid point of the sinew being to keep the bow from breaking."
I can attest to this, as I recently finished up a short, high-crowned osage bow that got a narrow coarse of sinew along the top of the crown. It added about 5 lbs. of draw weight, helps hold the profile, and allows me to draw the bow farther. All of these are fantastic benefits, but it didn't increase performance in a way this thread is seeking to discover.
Cool thread by the way. Great to have you around Tim! :)
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PatM:
Sinew is much less stiff than wood and stretches several time farther, so making bow thickness double by using sinew instead of wood raises draw weight by about 4 times instead of 8, and does so safely, where wood would break.
Tim
Do you factor in that sinew and glue is not quite the same as dry sinew? I don't think a sinew glue matrix actually has the stretch numbers that people throw around for sinew.
I'm not clear if you glued the cotton on in reflex or not.
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Ok, here is my thought process. ( when I say that, be rrady to go so far out the box, you wont even know what way is up, it gets crazy out here ).
You need something light weight as a core. For that in aviation we use honeycomb. It has no strength in any direction but it resist compression well. But natural honecomb is not an option. So a corigation, like cardboard perhaps, using split bamboo shoots side by side width wise.
Incase thats a no go, the point is you need something that is more a filler than a solid rigid structure. So i thought about your whipped hide glue. I know if it were cooked it can become more solid. What about frying some rawhide, then soaking it in hide glue to make is stronger, then using that as a core?
This is where it gets real fruity... Sweet young thai coconuts have a very spongy shell. Use a knife a spin the coconut on a lathe, and peel off a long strip of this spongey husk, lay flat and let it dry. I bet that would work. If not, bananna peels, orange peel, watermelon rind, a split piece of sugar cane, palm leaf stem.... I cant think of everything, but thats a direction to look.
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The sinew on Inuit cable bows and similar was not highly elevated and not of large enough diameter to raise draw weight as in this case. And possibly the sheer-slippage situation too. Their ingenuity went simply into getting a working bow at all, from no apparent makings. If they'd had decent wood they likely would't have bothered with sinew.
Tim
Tim, there are certainly some examples of crudely made Inuit cable bows, but I hope you are not overlooking some of the more similar finely made cable bows found further south. Perhaps a thread investigating some better examples would be worth persuing at another time?
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PatM:
Yes, hide glue won't stretch as far as sinew. The small-diameter bends on some Asiatic composites sometimes show the whitish shatter of the over-stretched surface glue. But no need for the sinew to be stretched that far here, and hide glue is the only game in town anyway.
Mild reflex when the cotton was applied, taken to 5" for the sinewing. But this is all proceeding by braile at this point; lots of trial and error bows needed before ideal ratios and materials come in to clear view. It might have been just semi-luck that the ratios and materials used in this first test bow worked out so well. The law of averages pretty much insists that it can be improved on.
sleek:
Possibly the main quality the elevator should have is that it no add to belly compression load. mass maybe not at important. I'll give some of your suggested Thai coconuts a try...
willie:
I've checked out the cable bows pretty well but likely haven't see all extremes of design. If you come across any of interest here please to let us know.
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1. Here is a drawing (from Murdoch) of a heavy sinew cable southern eskimo, the cable scales at 1/2" dia.
2. A photo some Haida bows, one with an elevated cable.
From https://anthro.amnh.org/anthropology/databases/common/image_dup.cfm?catno=16%20%20%2F%20%20%2033
3. A photo of a birch backed/compression wood spruce limb that failed in shear. It once had a rather heavy elevated cable. The 40" bow was pulling 70# @ 22" when it "slipped". It is 1.1 inches wide.
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Tim, whats the ideal thickness of the core for you?
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I GOT YOUR ANSWER!!!!! CHOLLA CACTUS!
Its a natural honey comb :D And its woody and super light weight. It will have some compressive resistance, which you dont want BUT.... if you cut it up int 1 inch or half inch long pieces, and butt them up against eachother, as the bow bends and sinew stretches, rather than add compression to the belly, the belly will force the cuts to open up and stretch the sinew more. If this wont do what you want, I dont know if what you want can be done. This stuff is the perfect core. Im sourcing some tomorrow to build one ASAP!
SORRY, Im excited :BB
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sleek;
The cotton/glue on the present bow is about 25% of finished bow thickness, the sinew about another 25%. I don't know yet if these ratios are ideal, and a lot depends on the bare bow's original thickness and draw weight.
willie:
Thanks for the graphics. I've been pondering those and similar bows for 30 years--If you have TBB-1 page 110 shows early experiments. The Murdoch and Haida bows had similar limitations and problems. On the Murdoch bow the sinew is not elevated so it's capacity to do work was limited; as with typical whole-back sinewing, draw weight would rise just a few %. And since the sinew cable stretches more than the wood back the energy usually stored by resisting sheer would be lost. And the friction of the cable against the wood costs some energy. All of this together means a relatively inefficient bow compared to a conventionally sinewed wood bow, and possible a typical self bow too. The Haida bow has a quite low volume of sinew, and there's the no sheer-energy problem. Not an efficient bow, but at least it was a bow. And really, that all they were aiming for. If the sinew volume had been higher, and both elevated and rigidly secured to the belly, the draw weigh and energy storage could substantially rise. But, from reports, they didn't have quality wood to allow this. Otherwise they'd likely have made all-wood bows as in most of the rest of the world.
Tim
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How thick of increase are you talking Tim ? I have a bunch of walnut veneer laying around that could easily laminated to any thickness or they sell it it in rolls up to 2 in. wide , unless I missed it what is your front view profile ? Plus your a big trouble maker my brain has been in over drive thinking about your project it's a refreshing thread (SH)
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Sorry I posted the same time as you thought I was the only one that worked on bows in the middle of the night ... Lol but I still think you could come up with a combination of lighter laminated cores the whole idea is based on raising thickness with out raising mass ?
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And since the sinew cable stretches more than the wood back the energy usually stored by resisting sheer would be lost............ The Haida bow has a quite low volume of sinew, and there's the no sheer-energy problem.
Tim, I am not familiar with the no sheer-energy problem. Shear seems to be touched on frequently in this thread, concerning both your design, and the traditional cable design. Are you suggesting that usable energy is stored in shearing forces? Perhaps you would be willing to expound a bit more about shear, or at least point to a resource that helps the bowyer understand how it needs to be a design consideration?
........... But, from reports, they didn't have quality wood to allow this. Otherwise they'd likely have made all-wood bows as in most of the rest of the world.
The northern Eskimos did not seem to have a good source of wood, and I agree that a cable might not be a very efficient way to store energy, my guess is that there is too much friction between strands (hysteresis) when retracting. But in spite of this inefficiency, it appears that a Haida yew paddlebow still benefited from the addition of a sinew cable, even in a wet environment. Maybe sinew has a lot more to teach us?
http://www.haidanation.ca/?p=1677
“Pacific yew is so closely tied with Haida tools and weapons that it shares its name with the paddle bow: hlG̲iid. In Haida Gwaii, these hunting tools are uniquely fashioned. The unusual Haida paddle bow is stripped of its sapwood. This design is thought to be well suited for canoe life, where waves and rain keep everything well soaked.
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Tim the chrono results will be very interesting,, thanks for sharing B :OK
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Stick Bender:
Thee in the morning when the world is asleep. A good time for serious pondering.
willie:
Take an 80lb bow at full draw and slice it in two along it's neutral plane. It's still at full draw, and essentially looks the same as before being sliced in two, but somehow now it's two 10lb bows instead of two 40lb bows, Why? And where was all of that extra energy hiding?
When whole, at full draw, the back was being stretched longer, the bell compressed shorter, high shear forces in play between the two, much energy stored as a result. At release the shear forces are free to return to zero, doing work in the process
If sinew is not rigidly attached to the belly then shear force between the two can't exit, and otherwise resulting stored energy won't exist.
The dynamics become way more interesting and complicated when seeking optimum designs where large-volume sinew is both elevated and rigidly attached. Not fully thought out yet.
Not enlarged on yet, there are problems when straining a uniform-diameter cable due to non-uniform stresses along it entire length. More later.
Early on I was infatuated with Haida and related designs but couldn't get them to perform as well as well-designed same-weight self wood bow. I love the idea of them, and would love to see one perform as hoped. Somehow it seems they deserve to.
Thanks for the targeted questions. They help sort things out.
Tim
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Willie:
Gee I'm dumb. That shear argument doesn't hold up. When at 80lbs most of the energy is stored at and near back and belly surfaces, shear not involved. Gotta think more before typing.
Tim
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If sinew is not rigidly attached to the belly then shear force between the two can't exit, and otherwise resulting stored energy won't exist.
Tim, I think your explanation of shear forces is right on. And without force you cannot have energy, right again.
But you can have force without energy. You can push against a locomotive, but if it does not move, you have done no work. If you push harder and it moves, then energy is 1/2 the mass of the locomotive times the velocity squared.
A bow limb is 3 foot long piece of wood and you are trying to shear it along the length. Lots of force required, but if it doesn't deform to any significant degree, no appreciable amount of energy is stored. Your design still needs to be able to resist this force Of course all most all of the energy in a bow is stored in the back and belly because they actually stretch and compress.
I didn't mention earlier how much trouble it was making "cable nocks" for the bow pictured earlier. It started life about a foot and a half longer, but by the time I rebuilt the attachments three times, the bow was only 40" long. I was determined to build up the "cable nocks" until something else broke. The birch "back" under the bridges sheared at 70# pull. To keep the cables attached to the ends of the limbs, I added the birch blocks shown below. They are approximately 3/4" wide by 2.5" long, glued with a good epoxy. I suppose that a similar sized short lam of decent wood, at the ends of your limbs and on top of the bamboo, could anchor the ends of your sinew layer. Couldn't the remainder of your core be the whipped hide glue, so long as it was firm enough to not collapse and maintain the needed elevation?
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I picture a strip of this Maple moulding as a intermediate strip to raise the sinew.
Repair the gap in the non sponsor link and paste it.
https://w ww.royalwoodshop.com/mouldings/product/burlap-decorative-bur101/?
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This is cholla cactus. It is mostly air, very resisnt to being crushed, and woody. This would make a perfect core by cutting it down to strips, and laying sinew over it. I vant think if a more perfect way to do this.
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Willie:
Gee I'm dumb. That shear argument doesn't hold up. When at 80lbs most of the energy is stored at and near back and belly surfaces, shear not involved. Gotta think more before typing.
Tim
Tim, i can assure you that sheer forces there and are strong in the neutral zone. All of the compression forves at the belly are mirrored by the twnsion forces at the back, but it is sheer force that is the conversion factor between tension and compression. Energy is stored at the back and belly, but only because those at the surfaces where the energy accumulates. Its coming from the neutral plane. You could say the neutral plane is the compression and tension force generator, sending energy out to the flat surfaces above and below it.
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Is there a reason engineers named it the "Neutral Zone"? If all the stresses and strains were in the middle "I" beams would be "O" beams wouldn't they?
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Is there a reason engineers named it the "Neutral Zone"? If all the stresses and strains were in the middle "I" beams would be "O" beams wouldn't they?
All i know is that because its under 0 compression, and 0 tension, its the middle, so its neutral in those forces. But it is where all the sheer forces are located.
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This is cholla cactus. It is mostly air, very resisnt to being crushed, and woody. This would make a perfect core by cutting it down to strips, and laying sinew over it. I vant think if a more perfect way to do this.
I used to live in Santa Fe New Mexico when I was growing up and chollas were everywhere. When they died they left that woody Skelton. They are surprisingly resilient strong and somewhat flexible if I remember correctly. I remember trying to break them thick sticks as a bat with no avail. After I moved from there and got into bow making I have often thought of whether a bow could be made from them, maybe as a laminate. The problem i see is that they have all those whole (which would reduce mass) but if you used glue with them they would fill up with glue as dead weight which weighs more than the wood that might have been in it's place.
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I was playing with corn cobs yesterday, the hollow core is extremely light and extremely strong, glued side to side it would make an excellent cable bridge.
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This is cholla cactus. It is mostly air, very resisnt to being crushed, and woody. This would make a perfect core by cutting it down to strips, and laying sinew over it. I vant think if a more perfect way to do this.
I used to live in Santa Fe New Mexico when I was growing up and chollas were everywhere. When they died they left that woody Skelton. They are surprisingly resilient strong and somewhat flexible if I remember correctly. I remember trying to break them thick sticks as a bat with no avail. After I moved from there and got into bow making I have often thought of whether a bow could be made from them, maybe as a laminate. The problem i see is that they have all those whole (which would reduce mass) but if you used glue with them they would fill up with glue as dead weight which weighs more than the wood that might have been in it's place.
The trick is, dont use so much glue it fills up. Apply a layer of glue over it, lay your sinew down, probably best to use the long solid back strap piece, let it dry, then lay your shredded sinew over it.
The back strap sinew would act like a canvas covering the holes, and give a solid bed to attatch your sinew layers to.
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I was playing with corn cobs yesterday, the hollow core is extremely light and extremely strong, glued side to side it would make an excellent cable bridge.
I bet corn cobs would work great as well.
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Agreed, there is shear force at the neutral plane of a bending beam/bow, but since there is no movement at the NP no energy is stored. Energy is stored only as the back is stretched and the belly compressed.
Some thoughts on advantages the experiment-bow here should have over conventional self or sinew-backed bows:
Since draw weigh rose 400%, to normal draw weight, means the belly alone was initially of unusually low thickness/draw weight. Being so thin allows extreme reflexing, for exceptional early draw weight, for greater total energy storage.
Extreme reflexing draws the belly surface into extreme tension, reducing its surface compression load when drawn, and allowing deeper non-surface wood to carry a larger portion of the load.
Draw weigh rose 4 times but mass less than doubled, raising efficiency by reducing energy lost to limb vibration.
Arguments, suggestions and comments welcomed.
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Tim, People are probably talking about energy storage immediately on either side of the neutral plane when they say at or in the neutral plane.
The concern with the thin belly and moving compression deeper is that the material deeper is no longer a good material to resist compression.
No good if it suddenly wants to crease and fold.
I'm still skeptical that belly material is less stressed at full draw after being reflexed. Can't see how it can be shortened without being shortened.
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Agreed, there is shear force at the neutral plane of a bending beam/bow, but since there is no movement at the NP no energy is stored. Energy is stored only as the back is stretched and the belly compressed.
Yes. The back and belly are like batteries, storing energy. The energy is converted into the + and - at the NZ. The NZ gets its energy from the bow being bent, creating a potenial slip between the surface to be compressed and the surface to be stretched. The NZ takes the energy of slippage, and converts it into the other stresses. Technically, the NZ is under the cumulative stress of both the back and belly. I only broke it down like that to make it clear that there must be somethingin the NZ to make a bow work.
Some thoughts on advantages the experiment-bow here should have over conventional self or sinew-backed bows:
Since draw weigh rose 400%, to normal draw weight, means the belly alone was initially of unusually low thickness/draw weight. Being so thin allows extreme reflexing, for exceptional early draw weight, for greater total energy storage.
This makes sense to me. However be careful with a thin belly, the thinner you get, the more exact you must be with its thickness, or stresses will concentrate in its thinnest part, and it will fail in compression.
Extreme reflexing draws the belly surface into extreme tension, reducing its surface compression load when drawn, and allowing deeper non-surface wood to carry a larger portion of the load.
I disagree here. If the belly is very thin, you wont get much tension on the belly during reflexing. Thats why it is so easy to bend. The belly being so thin, the distanve of the surfaces to the bellys own NZ isnt great enought to leverage much sheer into the NZ. Whis is exactly what you are trying to do over all, use distance as leverage to force the NZ into more sheer. A thing belly being bent into reflex doesnt have extreme tension unless you bend it an extreme unrealistic amount.
Draw weigh rose 4 times but mass less than doubled, raising efficiency by reducing energy lost to limb vibration.
Cant argue with results, and those are fantastic.
Arguments, suggestions and comments welcomed.
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Normally it would take about a 50% increase in thickness for 400% increase. Tim, how much was your total increase in thickness, I am guessing more than double???
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Normally it would take about a 50% increase in thickness for 400% increase. Tim, how much was your total increase in thickness, I am guessing more than double???
Are you accounting for reflex?
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PatM:
" The concern with the thin belly and moving compression deeper is that the material deeper is no longer a good material to resist compression."
If I understand, that would be true in the case of bamboo, not regular wood.
" I'm still skeptical that belly material is less stressed at full draw after being reflexed. Can't see how it can be shortened without being shortened. "
Less stressed per energy stored: Picturing a bow with equal wood and sinew thickness for now: When reflexed the belly surface is in tension, the belly back in compression, the NP about at center. As the limbs begin to be pulled toward straight, the compressed belly back works to come out of compression, stretching the sinew attached to it, storing energy. At the same time the belly surface begins to come out of tension. As the draw proceeds the belly back comes fully out of compression, stretching the sinew further, storing more energy, the belly fully out of tension but under no compression as yet. Note considerable energy has been stored before the belly surface feels any compression strain. As the draw progresses, since sinew is far easier to stretch than wood is to compress, the NP will rest toward the back of the belly, the compression load now shared by both inner and surface wood, surface wood less strained than otherwise.
Sleek:
" I disagree here. If the belly is very thin, you wont get much tension on the belly during reflexing..."
The belly is about half the thickness of a same-weight all-wood bow, so can reflex far more, taking the belly to near-breaking tension.
Badger:
Thickness increase was 100%, double thickness, but sinew is much weaker in tension that weight went to 4 times instead of the 8 times if all wood.
PS: Thanks for starting this thread.
Tim
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Tim, you still need to cut apart a few well used bows that were protected by sinew or perry reflexing and see that the belly still gets squashed.
Not sure why just the case with bamboo. In your scenario the belly is a thin strip no matter what the material.
I agree that the back is storing more energy but still not sure that the belly is protected.
Again, sinew is "weaker" in tension but it's the glue/sinew combined that you need to establish numbers for.
Does anyone have that?
We would need to make a sinew/glue fake tendon and test that to establish a number.
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I'm still skeptical that belly material is less stressed at full draw after being reflexed.
I have to agree with Pat. Suppose a straight belly lam is reflexed and put into tension. While the bow is being braced, that belly goes from being in tension to a "no strain" condition when it is straight again (half way to being braced). When fully braced or drawn it has the same strain as it would have had, if the bow had never been reflexed when the sinew dried. At brace the back in the reflexed bow, would of course be strained more than the belly, because it's "no strain" condition is the more reflexed position.
Assuming that sinew is capable of more strain than bamboo, it might be worthwhile to start the layup with a naturally deflexed bamboo belly. (can bamboo be trained to dry into deflex?) This might allow the bamboo belly to be drawn further before taking set, of course the strain in the back would be higher, but that could be the way to utilize the potential of sinew.
Either way, this means that back tension is the primary contributor to the much desired "exceptional early draw weight". Experimentation with tension side qualities may have some real potential for honing designs, as the compression qualities of bow woods are generally already understood.
I have not really come to any conclusions about what strain percentages constitute an optimum balance between the energy stored in the back vs. stored in the belly, but do believe exceptional bows have the balance we hope to duplicate.
When reflexed the belly surface is in tension, the belly back in compression, the NP about at center.
NP about at the center of the belly lam? If so, I am confused. I would think that once the sinew is laminated, the NP of the limb might be above or outside the belly lam altogether, or at least so close to the belly back to mot make much difference. Perhaps I am misunderstanding the description of a NP inside the belly?
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PatM:
" The concern with the thin belly and moving compression deeper is that the material deeper is no longer a good material to resist compression."
If I understand, that would be true in the case of bamboo, not regular wood.
" I'm still skeptical that belly material is less stressed at full draw after being reflexed. Can't see how it can be shortened without being shortened. "
Less stressed per energy stored: Picturing a bow with equal wood and sinew thickness for now: When reflexed the belly surface is in tension, the belly back in compression, the NP about at center. As the limbs begin to be pulled toward straight, the compressed belly back works to come out of compression, stretching the sinew attached to it, storing energy. At the same time the belly surface begins to come out of tension. As the draw proceeds the belly back comes fully out of compression, stretching the sinew further, storing more energy, the belly fully out of tension but under no compression as yet. Note considerable energy has been stored before the belly surface feels any compression strain. As the draw progresses, since sinew is far easier to stretch than wood is to compress, the NP will rest toward the back of the belly, the compression load now shared by both inner and surface wood, surface wood less strained than otherwise.
Sleek:
" I disagree here. If the belly is very thin, you wont get much tension on the belly during reflexing..."
The belly is about half the thickness of a same-weight all-wood bow, so can reflex far more, taking the belly to near-breaking tension.
Badger:
Thickness increase was 100%, double thickness, but sinew is much weaker in tension that weight went to 4 times instead of the 8 times if all wood.
PS: Thanks for starting this thread.
Tim
Tim, I agree with your point on the belly on one condition. That being that a thin belly can bend farther in reflex than a thicker belly before it begins to fail in tension. You can bend a belly in reflex to the point if failure regardless of thickness, the only thing that changes in the bend radius. And perhaps I am daft for not taking what you said as having that meaning in the first place.
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Tim, looking at the extreem reflexed belly you are making, its like a rubber band when unbraced. It is trying to spring back flat, but pulling the sinew into tension, until the forces equal, then it stops.
As you brace it, the belly is still trying to pull its self back flat, against the sinew, and still is under tension, not compression, until past its half way point ( when the belly is flat ) of being braced. All the work you put into it, has just been to stretch the back, at the expense of NO added belly compression.
Looking at it like this, when the belly lam starts off as flat, you force it into tension to add reflex, the belly doesnt go into compression until it has been bent back flat and into the brace profile. I dont believe you add compresion forces by reflexing a belly, but only add tension to the back. Even as you draw the bow, the sinew is now trying to pull the back, back into its flar state, the sinew doesnt add compressive forces either. Only tje radius of the bows bend does.
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^ this is a thought in prgress. I reserve the right to be nuts.
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I've been away from the scene for a time. Are there any critically witnessed fps numbers for 10gpp arrows from sinew-backed wood bows, with string type and mass noted?
PatM:
" Tim, you still need to cut apart a few well used bows that were protected by sinew or perry reflexing and see that the belly still gets squashed."
It's sort of apples and oranges. The sinew on such bows was relatively thin, meaning the wood was about as thick as if not sinewed, so suffered much of the same degradation as a non sinewed bow of the same weight. Here the sinew doubles the thickness of a thinner limb, causing the NP to rest near the sinew, compression strain therefor supported not just by the belly surface, inner wood carrying much of the load.
" Not sure why just the case with bamboo."
Interior bamboo is weaker than surface bamboo
"In your scenario the belly is a thin strip no matter what the material."
The belly is just about half as thick as a same-weight bare-wood would be.
Good idea, and worth doing: Measuring the stiffness of a fake sinew-glue tendon.
willie:
" I would think that once the sinew is laminated, the NP of the limb might be above or outside the belly lam altogether, or at least so close to the belly back to mot make much difference. "
That's right; the NP is in close to the sinew, meaning that more of the belly thickness in made to do compression work, not just the belly surface as per usual.
The position of the NP would shift bellyward a bit if sinew/glue is stiffer than sinew alone as PatM thinks might be the case.
Tim
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Ok, Tim, I've been thinking about this very thing for a while, never getting around to trying my prototypes. So. A few ideas.
1. Rough tiller a thin bow, maybe 1/4" thick, bamboo or wood. Spiral wrap the entire thing in 1/8" dia hemp craft cord. Sinew back OVER the cord wraps, thus using using the cord to "lift" the sinew. Secure sinew at tips. Cut off all the cordage on the sides and belly of the bow, leaving short parallel pieces running across the bow while the sinew runs lengthwise.
2. Belly lam of wood or bamboo, center core of rattan splints, sinew backed.
3. Mollegabet style bow with wide shoulders and 60/40 bending limb/lever rstio. Could be bamboo. Sinew or silk cable is wound round from shoulder to shoulder, similar to the silk/bamboo bow from TBB. Then flax or other "STIFF" cable is run UNDER the stretchy cable at the shoulders and back to the limb tips. Dual cable system forces middle cable to stetch, but creates stiff levers.
Also. same as above, but lever is shortened and recurved. A few small diameter bamboo sections laid crosswise act as string bridges and flax cable can be bound down to recurve. A cross-hatching wrap of cables can even be arrangel to improve stability of recurve.
4. Small diameter, thicker walled bamboo is split and tiller roughed out. This creates a "U" shape. The bow limb is then wrapped candycane fashion witb twine, but in both directions (as the Meares Heath artifact was wrapped.) Now, the bow can be cable-backed, the cable riding atop the twine wraps which span the open end of the "U".
Alternatively, the "U" cross section bamboo bow limb is backed with a linen fabric strip, such that the fabric spans the open top of the "U", and the fabric laps over the sides however much needed. This creates a hollow limb.
Both these designs take advantage of the Poisson Effect. The "U" cross section would attempt to flatten when bent but the wraps or the fabric would not allow it, increasing stiffness per mass.
Has anyone tried multiple cables? Say three or four running abreast, following the front profile contours of the bow by riding in small grooves set into the string bridges.
More to come.
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Good idea, and worth doing: Measuring the stiffness of a fake sinew-glue tendon.
I agree, A sinew in glue matrix might be different in both stiffness and elasticity, compared to sinew alone or wound into a cable. If you should happen to premake the sinew layup, I hope it could be successively applied on a bow with open bridges (attached only on the ends), one with a lightweight core and one with a conventional maple core.
Earlier I suggested that no work was being done in shear. I have reconsidered as there may well be shear deformation at the cellular level that contributes to energy storage in the limb. Hold a paperback book by the spine with one hand and moderately pinch the opposite edge with the other hand, then bow the book. There is a little bit of shear between each page. Imagine if the pages were glued with a flexible glue (the lightweight core condition), and finally if the pages were glued with a hard glue. All three limbs would differ in their stiffness or stored energy per thickness, and each have their own degree of hysteresis.
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Tim, I hope you don't think we're jumping on you like a pack of rabid dogs >:D. I think it sounds super interesting, just trying to understand it. I appreciate you joining and look forward to your future posts. You're practically a legend to me for your pioneering work in bow-making, using your scientific approach to dispel dogma and all. Now you can see we're skeptical of everything including your new ideas haha. I personally would love to see this bow you made. Do you have any pictures? Maybe you've tested it in a chronograph?
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willie:
To prevent failure at weak points a cable must be of uniform diameter it's entire length. But the wood is tapered in width and/or thickness. Intuition is throwing a shower of red flags. Pondering the problems and solutions now. Meanwhile, the present configuration of this experimental bow eliminates the problems.
Using a maple core would effectively be the same as starting with thicker wood.
If the glue is rubber-like, allowing some sliding between back and belly slats, for example, there would be a small amount of energy stored in the rubbery glue, but far less total energy stored due to reduced stretching of the back and compression of the belly. If the glue is rigid, not allowing the back and belly slats to slide, there is no energy stored in shear, all energy again stored chiefly at and near back and belly surfaces.
gfugal:
Thanks for the kind words, but don't stress; skepticism is valuable and appreciated, and it's been positive and civil. It's following pure Comstock protocols: "We're of no value to each other if we can't disagree." I'm brand new here and don't know the photo posting ropes yet. I think I've sent Badger--Steve--a photo of the bow, or if not I will, and maybe he can post it. Steve is going to the MoMeet shootoff in couple of months so I'm making an updated version for him to shoot there. Steve lives not far away so when I finish the tillering touchup with sinew we'll chrono the present version and post the results.
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Tim. "
" To prevent failure at weak points a cable must be of uniform diameter it's entire length. But the wood is tapered in width and/or thickness. Intuition is throwing a shower of red flags. Pondering the problems and solutions now"
My (limited) experience with cable backs tells me that it doesn't matter that the cable back is uniform diameter. A cable of uniform diameter and strength, pulled from both ends, must stretch uniformly. A wooden bow core, as you mentioned, must taper in thickness and/or width. Some minor adjustments to tiller must be made, but barring a restrained or anchored cable, tiller can still happen.
For reference, imagine we back a bow with a zero-stretch backing like a steel strap. Terrible performance, of course, but the bow could still be tillered to desired bend, ya? So, why wouldn't that be true of a back that stretches uniformly?
I also just realized that one could easily sinew back over a linen cloth cover (as on the hollow-limb bow from my previous post). Just gotta cut a strip of linen from the cloth diagonally, so it still creates a tight span laterally, but offers less longitudinal resistance.
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Tim, I dig the idea myself, but let me see if I understand the actual technical problem. Ideally, we use half the belly thickness, a spacer, and a sinew back, to equal the energy storage potential of a solid limb, but with much less mass.
The issues I see are that whatever the "spacer" material is, it must allow the glue to anchor the sinew to its surface. Without the "spacer" anchored to both backing and belly, you essentially have an irregular, flat cable and string bridges. So, we are looking for a spacer much lighter than wood, but strong enough to apply sinew directly to so the sinew acts as if applied to a regular wood core, e.g. not shifting or sliding around, and maintaining its position and function opposite its corresponding belly segment.
The shear forces don't really worry me, here, except that any version if this I imagine has the likely problem of the middle layer being too soft to hold the backing and belly correctly relative to each other.
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PatM:
Sinew stretches about 8% according to the tests here, which also gives it's elastic modulus/stiffness:
https://journals.openedition.org/ceroart/5152?lang=en
In a sinew backing the volume of glue is small compared to the sinew, so it should have a relatively smaller effect on the stiffness of the two together.
Here Dick Baugh measures the stiffness of sinew:
http://www.primitiveways.com/secrets_of_sinew.html
Springbuck:
A back is as stiff as it's least-stiff area. If the cable is not uniform in diameter the narrow less-stiff areas would seem to represent the net stiffness of the back, the thicker areas being partially dead weight. The thinner areas will be stretched farther than thicker areas, possibly to failure. -- Even though the thicker area are harder to stretch I need to determine if they actually are storing less energy per mass than the thinner areas. Intuition isn't dependable.
The spacer doesn't have to be especially light. This test bow's spacer is sinew-heavy yet draw weight rose 400% without quite doubling in mass.
Yes, if two slats of wood they must rigidly be keep from slipping in relation to each other.
But this might not be absolutely the case if the back is sinew:
Image a semi-rigid spacer, rigid enough to prevent the narrow outer-limb sinew from stretching dangerously more than the wider gripward sinew, but flexible enough to not fail when drawn from large reflex to a full draw
That's essentially the case with this bamboo/cotton-glue/sinew test bow. Surely not optimum, but worth noting.
But argue back.
Tim
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Is the glue fraction actually that small in a typical backing?
Still not sure why you want a spacer but are averse to a wood space.r
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willie: To prevent failure at weak points a cable must be of uniform diameter it's entire length. But the wood is tapered in width and/or thickness. Intuition is throwing a shower of red flags.
My (limited) experience with cable backs tells me that it doesn't matter that the cable back is uniform diameter. A cable of uniform diameter and strength, pulled from both ends, must stretch uniformly. A wooden bow core, as you mentioned, must taper in thickness and/or width. Some minor adjustments to tiller must be made, but barring a restrained or anchored cable, tiller can still happen.
I believe the adjustments have to planned for. I have some glue curing on one of Springbucks cable prototypes, hope to post the bow in a few days.
BTW, Spring buck . "A cable of uniform diameter and strength, pulled from both ends, must stretch uniformly." seems like reasonable assertion, but I have seen industrial examples that don't work that way. Enough for now, but if it seems to be relevant later in the discussion, I can describe the example, but have no explanation why it happens.
The thinner areas will be stretched farther than thicker areas, possibly to failure. -- Even though the thicker area are harder to stretch I need to determine if they actually are storing less energy per mass than the thinner areas. Intuition isn't dependable.
Can I make an educated guess? If you spliced three equal length lines end to end, such that each outer third was made from 3/4 inch line and the middle third was 3/8 in dia, and stretched it to failure, (assuming that the line parted in the middle of the smaller dia. line), what would be the reaction? I think smaller dia. ends of the center third would react much more violently than the outer thirds, much snap back, especially if it is a stretchy materiel. It stretched further and stored more energy per mass. If the energy storage was proportional to the mass, the snapback would be uniform for the entire spliced line.
Tim, you have made the claim a few times that doubling thickness of your stave yielded approx 400% increase. Is that the same as 4 times the stiffness? I thought that a doubling of thickness was supposed to increase stiffness 8 times in a uniform materiel. Different people figure percentages different ways. One common method is ...the difference between loads divided by the original load.
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Part of the uniform cable problem is that it carries unnecessary mass out at the tips. A lot of these experimental designs look promising and then they get dragged down by all the unforeseen extras.
Springbuck mentions all sorts of lashing and bracing with extra strands which all has to be put in motion.
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(=)any chrono results,, :NN
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Probably waiting for the touch up sinew to cure.
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What if one were to use praying mantis cocoons as the bridge? This things are tough as nails and light and flexible all in one! Just an ideer.
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PatM:
According to tests at this site hide glue stretches about the same % before breaking as sinew.
https://journals.openedition.org/ceroart/5152?lang=en
"Is the glue fraction actually that small in a typical backing?"
Before a bundle of sinew is set in place the excess glue is stripped out and off of it, a relatively small amount of glue, left.
" Still not sure why you want a spacer but are averse to a wood space."
Adding a wood spacer would be like starting with a thicker belly to begin with.
willie:
" Tim, you have made the claim a few times that doubling thickness of your stave yielded approx 400% increase. Is that the same as 4 times the stiffness? I thought that a doubling of thickness was supposed to increase stiffness 8 times in a uniform materiel."
If you double the thickness of wood then stiffness increases 8 times, but if you double wood's thickness using sinew instead of wood it increases about 4 times, sinew being less stiff than wood.
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PatM:
According to tests at this site hide glue stretches about the same % before breaking as sinew.
https://journals.openedition.org/ceroart/5152?lang=en
"Is the glue fraction actually that small in a typical backing?"
Before a bundle of sinew is set in place the excess glue is stripped out and off of it, a relatively small amount of glue, left.
" Still not sure why you want a spacer but are averse to a wood space."
Adding a wood spacer would be like starting with a thicker belly to begin with.
You still need to test the mixture of the two. Composite materials are known for "the whole being greater than the sum of the parts". I realize they are both the same material but the molecular structure is not. You wouldn't replace a tendon with a medical 'gummy worm" even if you dried it first.
However if they did actually have the same tensile strength after longer curing then the glue wouldn't give on so many sinewed bows.
Even if most of the glue is stripped out or squeezed out it still amounts to a fair additional mass amount.
The point about the wood core was the assumption that reflex would be glued between it and the belly material. It wouldn't be just a thicker belly then.
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PatM:
" You still need to test the mixture of the two. Composite materials are known for "the whole being greater than the sum of the parts... "
For the fun of the argument let's say a sinew cable was created, the sinew strands prevented from slipping past each other not by twisting or glue, but by a massless magic force. I think we're agreeing that a same mass cable made of hide glue would stretch roughly as far without breaking as the sinew cable, and have roughly the same stiffness. But you suspect that by combining them one or both will then have substantially different properties. I'd bet the difference, if any, would be too small to matter, but it's valid question. Seems impossible to prove though, because a same mass sinew cable can't be constructed: glue would void the test, and twisting affects both the mass per length of the cable and its stiffness.
" However if they did actually have the same tensile strength after longer curing then the glue wouldn't give on so many sinewed bows."
Different batches of hide glue vary in tensile strength and % of stretch by more than double.
https://journals.openedition.org/ceroart/5152?lang=en
If glue in a sinew backing fails sometimes it make sense that it's a weaker versions of it.
A useful footnote: store-bought gelatin makes exceptionally strong glue
" Even if most of the glue is stripped out or squeezed out it still amounts to a fair additional mass amount.
I just weighed an ounce of dry sinew and an ounce of dry powdered hide glue. The sinew volume seems maybe 50% greater than the glue, but hard to tell for certain. (used powdered glue to more closely match the spaces between strands of hide glue) But lets figure sinew has 100% greater volume. In that case, even if most of the glue is squeezed free of the sinew a somewhat significant mass amount could still remain. A lot would depend on the diameter of the sinew strands of course. The finer the strands the more glue would be incorporated. Which leads to this question: what is ideal stand girth for strongest per mass sinew backings?
" The point about the wood core was the assumption that reflex would be glued between it and the belly material. It wouldn't be just a thicker belly then. "
Please explain this fuller, I don't fully understand.
This has been good line of discussion.
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PatM:
" You still need to test the mixture of the two. Composite materials are known for "the whole being greater than the sum of the parts... "
For the fun of the argument let's say a sinew cable was created, the sinew strands prevented from slipping past each other not by twisting or glue, but by a massless magic force. I think we're agreeing that a same mass cable made of hide glue would stretch roughly as far without breaking as the sinew cable, and have roughly the same stiffness. But you suspect that by combining them one or both will then have substantially different properties. I'd bet the difference, if any, would be too small to matter, but it's valid question. Seems impossible to prove though, because a same mass sinew cable can't be constructed: glue would void the test, and twisting affects both the mass per length of the cable and its stiffness.
" However if they did actually have the same tensile strength after longer curing then the glue wouldn't give on so many sinewed bows."
Different batches of hide glue vary in tensile strength and % of stretch by more than double.
https://journals.openedition.org/ceroart/5152?lang=en
If glue in a sinew backing fails sometimes it make sense that it's a weaker versions of it.
A useful footnote: store-bought gelatin makes exceptionally strong glue
" Even if most of the glue is stripped out or squeezed out it still amounts to a fair additional mass amount.
I just weighed an ounce of dry sinew and an ounce of dry powdered hide glue. The sinew volume seems maybe 50% greater than the glue, but hard to tell for certain. (used powdered glue to more closely match the spaces between strands of hide glue) But lets figure sinew has 100% greater volume. In that case, even if most of the glue is squeezed free of the sinew a somewhat significant mass amount could still remain. A lot would depend on the diameter of the sinew strands of course. The finer the strands the more glue would be incorporated. Which leads to this question: what is ideal stand girth for strongest per mass sinew backings?
" The point about the wood core was the assumption that reflex would be glued between it and the belly material. It wouldn't be just a thicker belly then. "
Please explain this fuller, I don't fully understand.
This has been good line of discussion.
A glueless sinew cable is easy to find. It's called a dried whole tendon. ;)
Not sure what the final moisture content was in the tested samples linked to but I'm skeptical that the glue was at full strength after what seems a rather brief cure.
Maybe weigh a slim tendon rather than trying to estimate a pounded fluffed up strand of sinew.
I no longer pound sinew to process it.
I meant that the core and belly would have perry reflex themselves rather than just being a single thicker piece.
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A photo of the bow was posted on the PaleoPlanet site. It's the 11th posting down on this thread:
https://www.tapatalk.com/groups/paleoplanet69529/how-much-can-a-sinew-backed-bow-be-reflexed-withou-t66178.html
The next version will be longer, have far more reflex, a rectangular-section sinew back, elevated a bit more than on this first test version.
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Tim...Most times after it's done and cured fully with the normal squeezing out of glue from sinew before applying it on the bow the glue ends up weighing about 1/3 of the total sinew glue matrix applied on the bows.The 30 to 40 percent glue mass weight was the ideal weight to achieve.This can be a little variable as to how thick the glue is too when using,but in general a little thicker glue used while sinewing than used while sizing.I seem to remember Pat and me had a discussion about this on here in the past.
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BowEd:
What method did you use to determine the 1/3 figure? Can you say a step-by-step?
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Tim, while we are waiting Springbucks reply, could you clarify?
Image a semi-rigid spacer, rigid enough to prevent the narrow outer-limb sinew from stretching dangerously more than the wider gripward sinew, but flexible enough to not fail when drawn from large reflex to a full draw
That's essentially the case with this bamboo/cotton-glue/sinew test bow. Surely not optimum, but worth noting.
Are you suggesting a purposeful and localized amount of slippage in parts of the limb might be helpful?
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Tim....I diagnosed that from pre weighing everything from start to finish on a scale.Scale I used measures down to the 1/20th of an ounce increments.So that's about a 22 grain variable.Writing it down so I don't forget....lol.As an example.Weigh amount of sinew/weigh bow prior to sinewing.Final weight reweighed after curing 4 months.Difference will be the amount of glue on bow.I did use Pat M's method of wrapping and smoothing of sinew after sinewing to reduce sanding of sinew too with some minor sanding and light resizing between applications of sinew.I usually apply sinew in 3 applications increasing reflex with reverse bracer a bit more each time.Latest bow's numbers came in at 2.64 ounces of sinew and half that 1.32 ounces of glue.For a total of 3.96 ounces of sinew glue matrix.
Problem can come from that sinew curing more the next six months to a total of 1 year draw weight would still increase but not decreasing mass weight.So retillering down draw weight is required.After 4 months curing decrease in mass weight is very very minimal with sinew/glue mass amount as I'm sure you know already.
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FWIW the natural "glue" holding together a living tendon contributes to the ultimate tensile strength and stiffness of the tendon. That makes me think that sinew in a glue matrix enhances that too, especially since it gets cured and dried.
Tendon actually starts to fail at about 3.5% and then totally fails beyond that point according to some studies.
So I think a typically reflexed sinewed bow drawn to closer to the belly wood limit probably brings sinew closer to its failure point than typically mentioned.
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Seems that a whipped glue matrix will crack, crumble and fail as it is bent, then sinew stretching and pushing down on it. The sinew will delam from the belly if that happens.
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Tim says: A back is as stiff as it's least-stiff area. If the cable is not uniform in diameter the narrow less-stiff areas would seem to represent the net stiffness of the back, the thicker areas being partially dead weight. The thinner areas will be stretched farther than thicker areas, possibly to failure." Even though the thicker area are harder to stretch I need to determine if they actually are storing less energy per mass than the thinner areas. Intuition isn't dependable.
So, this I knew already from reading your stuff, etc. , and I believe it's totally accurate. Let me add that a sinew cable is usually made of multiple smaller strands in order to eliminate weak and thin spots in the same way multiple strands benefit a bowstring, for that very reason.
Tim Says: Even though the thicker area are harder to stretch I need to determine if they actually are storing less energy per mass than the thinner areas. Intuition isn't dependable.
Intuition is NOT dependable, true. But, since sinew is SO elastic in tension, I doubt it is analogous to, say, limb thickness. We know a thick limb even even a small amount stores a BUNCH of energy. I may be wrong, but it seems to me that energy storage through elastic stretching is more dependent on travel, but that any amount of stretch stores energy. This should be testable by snipping a wide rubber band slightly narrower in one spot. I do however believe strapping or anchoring a cable down in one or several spots can change everything.
If the spacer DOESN'T have to be light weight, why are we using the glue-soaked cotton and not some other material? Or am I missing the point entirely of your design?
Tim says: "Yes, if two slats of wood they must rigidly be keep from slipping in relation to each other. But this might not be absolutely the case if the back is sinew."
OK, but I'm fairly sure it needs to be anchored at least somewhat to the belly to maintain their positional relationship.
What I mean is, I'm imagining a paddle bow, backed with sinew which covers the whole face of the back. The sinew back is essentially the same front shape as the belly. Now, similar to your experiment here, we somehow lift the entire sinew back and add a "spacer".
IF the sinew backing now floats unsecured atop the spacers, bound to the belly only at the tips, or even tips and handle, it basically becomes a badly misshapen, flat cable, over-stressed where it is narrowest.
IF, however, we do what you did, using glue-soaked cotton, the cotton is glued to the belly and the sinew back is glued to the cotton, indirectly anchoring the back to the belly.
Am I understanding this correctly? Does the cotton serve any functions I'm not imagining, besides anchor and spacer?
Tim says: Imagine a semi-rigid spacer, rigid enough to prevent the narrow outer-limb sinew from stretching dangerously more than the wider gripward sinew, but flexible enough to not fail when drawn from large reflex to a full draw
That's essentially the case with this bamboo/cotton-glue/sinew test bow. Surely not optimum, but worth noting."
That answered my question......
BTW, I'm ok to argue, but I mean to feed you ideas and perspectives that may help you further develop the idea.
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Is the glue fraction actually that small in a typical backing?
Still not sure why you want a spacer but are averse to a wood spacer
I think of it this way, Pat. I don't do a lot of sinew myself, but I do know I can sinew back a bow with no more than two packets of Knox gelatine for glue, that together don't make a dry tablespoon, and weight about what a sheet of paper does.
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willie: BTW, Spring buck . "A cable of uniform diameter and strength, pulled from both ends, must stretch uniformly." seems like reasonable assertion, but I have seen industrial examples that don't work that way. Enough for now, but if it seems to be relevant later in the discussion, I can describe the example, but have no explanation why it happens."
Yeah, THAT is something I would like to see and understand better.
willie: Tim, you have made the claim a few times that doubling thickness of your stave yielded approx 400% increase. Is that the same as 4 times the stiffness? I thought that a doubling of thickness was supposed to increase stiffness 8 times in a uniform materiel. Different people figure percentages different ways. One common method is ...the difference between loads divided by the original load.
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Double thickness = 8 X stiffness works for wood. Sinew is both more stretchy and EASIER to stretch than wood. Per mass.
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Part of the uniform cable problem is that it carries unnecessary mass out at the tips. A lot of these experimental designs look promising and then they get dragged down by all the unforeseen extras.
Springbuck mentions all sorts of lashing and bracing with extra strands which all has to be put in motion.
Yes, that is true and I've given it a lot of thought. For instance, using 1" bamboo to make the "U" shaped cross section would mean I need to solve a problem with my tips being almost as wide and massive as the rest. Definitely would need to be managed.
However, if you START with half the original necessary mass, you have a lot of wiggle room. The lashing and binding I'm talking about is on the scale of 20 feet of twine, and will weigh much less than half the wood mass of a limb.
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You could probably use two tapered bamboo halves spliced together at the center. A thickness taper would get you a reasonable narrowing. Bamboo is thinner walled farther out so you'd retain the hollow center.
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Is the glue fraction actually that small in a typical backing?
Still not sure why you want a spacer but are averse to a wood spacer
I think of it this way, Pat. I don't do a lot of sinew myself, but I do know I can sinew back a bow with no more than two packets of Knox gelatine for glue, that together don't make a dry tablespoon, and weight about what a sheet of paper does.
How many layers?
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The amount of glue for Tims' bow mass weight wise should'nt need to be more than 290 grains or so.With the balance in weight in sinew making up to the 2 ounces put on the bow.So my estimation of sinew applied without knowing would be around 580 grains or so of sinew used.It's a fairly significant layer of sinew used.On a bow 46" long put on full length it would probably end up a barely 1/16" thick.Depending how wide the limbs are of course as that was'nt stated.
I would think if the bow was at least 1.5" wide you would have a hard time making the sinew layer flat on a crowned back without leaving the center area a bit light in thickness.So here comes the cotton to make that flat first.Then the sinew on top of that flat cotton.
I see what Tim is doing.That's for sure.Interesting.
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sleek said: "Energy is stored at the back and belly, but only because those at the surfaces where the energy accumulates. Its coming from the neutral plane. You could say the neutral plane is the compression and tension force generator, sending energy out to the flat surfaces above and below it. "
Yes! I wouldn't have phrased it quite this way, but, yes.... the neutral plane like is the fulcrum of a teeter-totter.
Belly compresses, but it WANTS back to stretch. Back stretches, but it would rather force belly to compress. I don't think the shear forces actually STORE much energy (because shearing is all or nothing, catastrophic) but the whole rest of the bow must EITHER store energy by bending, or shear and collapse.
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A glueless sinew cable is easy to find. It's called a dried whole tendon. ;)
I meant that the core and belly would have perry reflex themselves rather than just being a single thicker piece.
Biologically, a whole, dried tendon is FULL of glue. It was just produced in place by a cellular process.
And, a sinew backing cannot pull itself into "Perry reflex" as it dries, just reflex. Those are mechanically very different things, let alone different by definition.
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That glue however is designed to work in "wet" form. It's far more complex than just hide glue.
You misunderstood the perry reflex comment. I meant that the core material and belly would have perry reflex between them and the sinew and core would also have it between them because the sinew would be applied with the core material in feflex as well.
The increased reflex from drying is just gravy. The sinew is already functionally shorter because of the way it was glued on.
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sleek said: "Energy is stored at the back and belly, but only because those at the surfaces where the energy accumulates. Its coming from the neutral plane. You could say the neutral plane is the compression and tension force generator, sending energy out to the flat surfaces above and below it. "
Yes! I wouldn't have phrased it quite this way, but, yes.... the neutral plane like is the fulcrum of a teeter-totter.
Belly compresses, but it WANTS back to stretch. Back stretches, but it would rather force belly to compress. I don't think the shear forces actually STORE much energy (because shearing is all or nothing, catastrophic) but the whole rest of the bow must EITHER store energy by bending, or shear and collapse.
Im glad you get it. As for any energy being stored in sheer, id wager that is what we call hysteresis. Its not actually stored energy, but energy lost, as Tim ( i think but maybe someone else ) puts it, due to internal friction.
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Belly compresses, but it WANTS back to stretch. Back stretches, but it would rather force belly to compress. I don't think the shear forces actually STORE much energy (because shearing is all or nothing, catastrophic) but the whole rest of the bow must EITHER store energy by bending, or shear and collapse.
this thread has me thinking a little bit different about shear and energy storage. the cells in wood are a bit longer than those in the pic, but they are not free to slip along side each other. this resistance to slipping causes distortions in the cell walls, and the cells want to straighten when the load is released just like the tension or compression distorted cell want to return to it's original shape. In fact this resistance to shear causes the compression and tensile stretching. If the cells are free to slip, the limb has to be much thicker to resist the same bending load.
id wager that is what we call hysteresis. Its not actually stored energy, but energy lost, as Tim ( i think but maybe someone else ) puts it, due to internal friction.
hysteresis is when the cell does not want to return to shape rapidly.
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Could you use a, say, 1" dia. whole bamboo. That gives you a thin belly, light center(air) and a thin back to sinew to. Just spitballin"
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BowEd:
" Are you suggesting a purposeful and localized amount of slippage in parts of the limb might be helpful?
Did you mean " rigid flexible enough to prevent the narrow outer-limb sinew from stretching dangerously"
The provisional thinking is that a spacer with some give in it would allow the sinew to be elevated without the failings of in-air sinew that narrows from grip to tip. Such sinew would be over-strained in its narrowed portions. A some-give spacer would be set in place with the belly in large reflex and firmly glued to belly and sinew. As it's braced and drawn the narrower portions of the sinew would struggle to over stretch but be prevent, only slight give in the spacer, all of the sinew made to work just as if directly glued to the belly, minus a small % of stored energy lost to the give.
BowEd:
I"ll do it in a slightly different way and see if we get similar figures: I'll weight a couple of ounces of sinew, apply glue as if applying it to a bow, but let each bundle separately air dry, suspended by a thread. They should dry quickly. 10 days should do it, but will wait till no weight loss whatever.
Sleek:
This dense-foam glue is really interesting. It's harder to thumb-nail dent than pine--just tested it--but is half the mass, per float test. The first batch was made accidentally by whipping powdered glue into hot water. Knox gelatin in this case. Being self-insulated, drying/shrinking time is long, It's probably not worth the trouble to fashion a large enough batch for the sinew spacer here, but might have other uses. It might be a new paleo technology.
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PatM: You misunderstood the perry reflex comment. I meant that the core material and belly would have perry reflex between them and the sinew and core would also have it between them because the sinew would be applied with the core material in feflex as well."
Ah, yes. I did misunderstand it, then.
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How many layers?
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Good question. How thick is a layer. I was thinking of a pretty short little West Coast kind of bow I tried once, and I put on two layers of bundles smaller than a pencil.
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Could you use a, say, 1" dia. whole bamboo. That gives you a thin belly, light center(air) and a thin back to sinew to. Just spitballin"
You could, and I had a similar idea about what I've heard call a "loose" laminate bow, where the bow is made by stacking thin lams that are not glued. (Essentially a bundle bow, but stacked slats, not sticks.)
But, the bamboo immediately UNDER the sinew then is still resisting the stretch. You really wouldn't get the most out of your sinew.
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"this resistance to slipping causes distortions in the cell walls, and the cells want to straighten when the load is released just like the tension or compression distorted cell want to return to it's original shape."
Oh, yeah! Their position relative to each other is probably more "fixed" than their shape.
"In fact this resistance to shear causes the compression and tensile stretching. If the cells are free to slip, the limb has to be much thicker to resist the same bending load."
Yup, kind of like a "loose laminate" bow. It takes a stack of lams to equal the stiffness of two lams glued together.
id wager that is what we call hysteresis. Its not actually stored energy, but energy lost, as Tim ( i think but maybe someone else ) puts it, due to internal friction.
hysteresis is when the cell does not want to return to shape rapidly.
[/quote]
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Could you use a, say, 1" dia. whole bamboo. That gives you a thin belly, light center(air) and a thin back to sinew to. Just spitballin"
You could, and I had a similar idea about what I've heard call a "loose" laminate bow, where the bow is made by stacking thin lams that are not glued. (Essentially a bundle bow, but stacked slats, not sticks.)
But, the bamboo immediately UNDER the sinew then is still resisting the stretch. You really wouldn't get the most out of your sinew.
Cut slits in the back so it opens up when bent rather than stretch, then lay sinew over that.
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hysteresis is when the cell does not want to return to shape rapidly.
Id say thats true, and i guess my statement was too absolute. Sheer must deform cells, and that deformation is wasted energy, as is it when the cells relax. A perfect core would be impossible to deform at all.
Modifing to say, the core should also offer no tension or compression abilities.
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Here is just another idea to throw out there.
Diagram shows half a pyramid limb. Yellow lines are 3/8" dia rattan cross-pieces bound in place with twine. Orange rounded rectangles are sinew cables, each varying in thickness or number of strands to correspond with its position on the limb: more toward the handle, fewer toward the tips. The green lines are just lashings of twine to keep the sinew riding down the middle of the bow.
Side view shows how the cables ride "in the air", but the fixed position of each cross piece forces the cables that correspond to THAT segment to stretch as much as that cable wants to bend.
My intuition tells me that the number of strands toward the tips will be lower than toward the handle, but that the amount of WOOD will diminish faster than the amount of sinew, which risks a tip-heavy bow, again.
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Here is one I HAVE done, experimentally.
Mollie-type, 1.75" wide bamboo slat, bent into reflex by tying down handle and placing limbs on blocks. Shoulders are cut in at nodes. (Black lines) The whole middle, from shoulder to shoulder, got a nylon cable (artificial sinew) that was run up the back, around the top shoulder, down the back, and around the bottom shoulder. Repeated a bunch of times. (orange lines in diagram) I THINK I followed the TBB; total diameter=1/5 area of the cross section of the base of the limb, about. Several rattan dowels were placed to bridge the cable.
The separated cable(s) were laced together with hemp craft cord in a zig-zag to center it/them. (light green lines) Then, a HEMP cable (darker green) was run UNDER the nylon at the shoulders, up the lever, and around a rattancross-peg lashed toward the tip, again with the lever in slight reflex. It cinches the nylon cable a lot more than the diagram shows. This cable was "set" by forcing the levers back straight, and bound in place. Then the whole bow was forced back to straight to "set" the nylon cable.
This bow bent fine, and I could adjust tiller by scraping the sides and messing with the string bridges. I don't remember ever shooting it, though, because I have a mental block about bows that wide and flat without narrowed handles, and couldn't see a way to build up and narrow it and still have it act like it had fades.
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Tim...I suppose that should work too.Although many times while sinewing while smoothing the sinew down laying it in place extra glue from my fingers goes on too.I should think doing it the way you propose will come in with a lighter weight of glue percentage yet is what I mean.
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Springbuck, in your first example, varying the thickness of the cables as you go down the limb may be a good way to "taper" the tension side. I assume that each bridge is well anchored to the limb so that the tension can step down as you move out the limb? Perhaps the bridges float and even though the entire cable assembly is under the same tension, the amount each cable stretches will change on account of each being successively smaller diameter, as you move out the limb?
Am building a bow that Springbuck and this discussion inspired. It is a bamboo HLD. About 5/8" wide and 42" overall. Hopefully it will survive to be the new shooter for an 8 year old.
Tim, do you mind that I post it here in the spirit of experimentation? I don't want it to take away from your work. If so, I can put it in another thread.
Without the bridges, the belly pulls 7.5lbs @ 10" draw. I hesitate to draw it further as the edges of the sectioned bamboo seem prone to raise a splinter, but hope to build a cable that will double that draw weight (is that reasonable?), placing the lips of the U section at the NP of the limb, and not have to be so concerned about raising splinters. When adding a cable to a previous bow the tiller changed, and I ran out of wood as I re-tillered the belly, but the bridges were of uniform height. This time, I think I can "mess with the bridge height" and keep the same bend. ie." tiller" the rest of the way with cable tension, bridge heights and placements, while leaving the belly as is.
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BowEd:
" ... many times while sinewing while smoothing the sinew down laying it in place extra glue from my fingers goes on too."
Might as well be totally accurate, so your above should be accounted for. So the new plan is to "sinew back" a piece of paper, applying the sinew just as if on a bow except separating the bundles a bit to speed drying. Part of the reason sinew on a bow has a long drying time is that much of the backing's water penetrates into the bow, the paper in this case preventing such, and allowing the bundles to dry on all sides. I'll weight the dry sinew and paper before, and once dry.
willie:
Elevating sinew makes it do more work, allowing a lower mass of it than otherwise to carry the entire tensions load, in turn allowing thinner wood, in turn allowing exceptionally large reflex. That's the gist of this thread, so anything related at all is valuable, everyone benefiting.
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BowEd:
" ... many times while sinewing while smoothing the sinew down laying it in place extra glue from my fingers goes on too."
Might as well be totally accurate, so your above should be accounted for. So the new plan is to "sinew back" a piece of paper, applying the sinew just as if on a bow except separating the bundles a bit to speed drying. Part of the reason sinew on a bow has a long drying time is that much of the backing's water penetrates into the bow, the paper in this case preventing such, and allowing the bundles to dry on all sides. I'll weight the dry sinew and paper before, and once dry.
willie:
Elevating sinew makes it do more work, allowing a lower mass of it than otherwise to carry the entire tensions load, in turn allowing thinner wood, in turn allowing exceptionally large reflex. That's the gist of this thread, so anything related at all is valuable, everyone benefiting.
I agree Tim.The wood itself absorbs that moisture a lot and has to leave too.Sounds like a good plan you stated.Quite a bit faster to find out doing it on paper.Don't think anyone has actually brought this to a complete experiment finding out exactly how much weight the glue is on line like this yet.Your bow too as an example of an experiment.It'll be interesting.
It might be some people squeeze out more before applying too,but should'nt be much.Consistency of glue[thin or thick] might be a factor. Somewhere in between should be good.I know it took me a while sinewing a few bows to get into a satisfying procedure.I really can't prove the 30 to 40 % mass glue weight final figure I come up with is ideal for strength,but just from sinewing many bows now that hav'nt failed.Some with reflex over 12".Pat M seems to think so.Think Adam Karpowiz has stated so too.Marc St. Louis has done a number of them himself besides others that I know not of.Loefflerchuck makes some authentic extreme all horn bows too.Actually never had sinew fail on a bow besides putting too much reflex on a red cedar....lol,and the glue and sinew did'nt really fail.It delaminated the red cedar with a resounding big big bang.I got away with not wearing a helmet on that one....lol.I think I might have had the red cedar itself just plain too thick to take the bend myself.Something to think about with the cotton being used.Delamination should'nt occur though if the reflex is'nt too extreme I would think.
You should pack a bag and drive up with Steve when he goes to Mo Jam this year with the bow.I and I'm sure many others I know who are bow makers were'nt fortunate enough to make the first get together when all of you guys got together to settle opinions.A lot of info was found out that's for sure.
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if there is natural glue in the tendon and it can be reconstituted by chewing and saiva, is there a possibility of modifying the modern application process to more closely resemble a "chew and glue" method? utilizing what is already there, and not having to add so much hide glue?
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if there is natural glue in the tendon and it can be reconstituted by chewing and saiva, is there a possibility of modifying the modern application process to more closely resemble a "chew and glue" method? utilizing what is already there, and not having to add so much hide glue?
I have no clue if thats possible, but I love the out of the box thinking. It would be nice to find a way to extract the glue without having to cook it out, as Im sure that degrades it.
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From
https://babel.hathitrust.org/cgi/pt?id=aeu.ark:/13960/t7br9bh8j;view=1up;seq=50
some techniques not often talked about with the application methods passed down from the old world. pretwisting strands and using a glue ball to rub the glue on
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willie: "I assume that each bridge is well anchored to the limb so that the tension can step down as you move out the limb?"
Yes, that is what I assumed. Either tied down hard with Boy Scout style lashing, or even set in slight recesses, something.
Are you planning to just add bridges, or back with the linen cloth first? Which version? I'm afraid that any flex will splinter the bamboo from a small diameter
willie: "This time, I think I can "mess with the bridge height" and keep the same bend."
I think so too. There is a great example of an arctic bow from the Smithsonian North American Ethnographic Collection with a cable that rest against the limb, except where a tiny spring bridge rests right in the deepest part of a recurved angle to prevent the recurve flattening out.
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if there is natural glue in the tendon and it can be reconstituted by chewing and saiva, is there a possibility of modifying the modern application process to more closely resemble a "chew and glue" method? utilizing what is already there, and not having to add so much hide glue?
I have no clue if thats possible, but I love the out of the box thinking. It would be nice to find a way to extract the glue without having to cook it out, as Im sure that degrades it.
Not all glue is actually cooked out like homemade stuff.
Gelatin for example is reduced by other methods.
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Like this.... sorry that pic is so tiny.
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if there is natural glue in the tendon and it can be reconstituted by chewing and saliva, is there a possibility of modifying the modern application process to more closely resemble a "chew and glue" method? utilizing what is already there, and not having to add so much hide glue?
Could be. The thing is that, chemically, hide glue and sinew are ALMOST exactly the same thing, which is collagen. The sinew also contains fibrin. Boiling out hide glue is just denaturing the protein one step back, When it dries it essentially goes through dehydration synthesis, which is not EXACTLY the same process as the living cells use that laid it down, but results in a very similar product. Saliva does the same thing chemically through an enzyme.
The real difference is that we may damage the protein during extraction (over-boiling, etc.) and we lack the precision alignment, matrixing, and perfect placement the living cells are capable of. But, there is glue (collagen) still in the sinew, and when we add more and remove water, hide glue BECOMES part of the sinew, part of what is already there, in a way no other glue does. We just can't do it as well as biology.
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Not all glue is actually cooked out like homemade stuff.
Gelatin for example is reduced by other methods.
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Yes, lots of chemical methods.
I just read an entire three page article on the process in "Uncle John's Bathroom Reader." Since they are using industrial food scraps there are a lot of steps, and purity must be very high, the process is really involved (acid baths to dissolve ground bones, saponification and skimming of the fats, etc.) but the article mentions extraction by boiling. That may have been to remove the chemicals from the previous step in the process, or whatever.
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To illustrate the difference in the actual structure of glue and tendon you could try backing a bow with a strip of jello and letting it dry.
How do you suppose it might fare as a backing?
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To illustrate the difference in the actual structure of glue and tendon you could try backing a bow with a strip of jello and letting it dry.
How do you suppose it might fare as a backing?
That's what I'm talking about.
Sinew has fibrin in it as well, and I suppose hide glue must have some denatured fibrin as well. Using collagen by itself would be absurd, of course, and we can't get denatured fibrin to lay itself out longitudinally without the help of cells.
But, you can extract glue from sinew by slow cooking, and you can essentially put it back by letting soaked sinew dry, just not as well as nature.
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Are you planning to just add bridges, or back with the linen cloth first? Which version? I'm afraid that any flex will splinter the bamboo from a small diameter
not sure why it should splinter?
making the bridges the same height as the limb is thick directly underneath the bridge seems to work to keep tiller, at least to the 10" draw curve I referenced yesterday. It keeps the same taper going I suppose. the first pull added 30% to draw weight but I have not started to twist the cable yet. Need to add a few more bridges and glue them all down well before cranking on the cable and making big full draw pulls.
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Using collagen by itself would be absurd, of course,
I have read where hide glue left on glass to dry, can shrink and lift a flake. never seen it tried, though.
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I'm just afraid it would, is all. :P
I understand the theory of the neutral plane, and how raising the cable or backing changes it. But, we are using a stetchy backing and there are spaces between the bridges, etc.. Hard to know until the first pull.
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willie:
Especially when approaching full draw, friction of the cable against the bridges might be great enough to drain measurable amounts of energy. Originally I thought that making the bridges toggle a bit would solve that problem, but later decided to let them roll instead. But never tried either. Your setup looks pretty friction free, so likely not worth the bother, but if ever curious, just replace the present bridges with same-height no-friction rolling ones and see if there's a performance change.
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I wonder how well black palm “heartwood” will do as a core?
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The 46" bamboo-cotton-sinew test bow, a touch of sinew-tillering needed.
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Wasn't sure hide glue would grip the cotton firmly enough to prevent it 'straightening itself' up off of the bamboo while drying, so lashed it in place with cotton string till hard dry. It held, so removed the string wrap, braced and drew it to 15". After touching up the tiller with sinew it will be tested at 20" and 22" with a 10gpp arrow. If it does well Steve/Badger will shoot it at the coming MO meet. And the next version too, if ready. It will have a rectangular-section sinew back, likely elevated as high as the crown top on this one, cotton spacer replaced by unknown-at-present.
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I see.Good picture.Filling concavity of bamboo with cotton.Then sinewing over that.
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if ever curious, just replace the present bridges with same-height no-friction rolling ones
Quite the idea, I am finding out with this narrow bow, that the bridges need grooves to keep the cable centered, and if the bridges were free to roll, they would also need tracks to run in. It might be interesting to shoot alongside some compound shooters at the club with something like this. you might have a hard time saying "just a different way to use wheels and cables, guys" while trying to keep a straight face.
In spite of the potential for improvements with the cable idea, the main impetus behind my experiment is to work out the "round cable vs tapered limb" question posed earlier, and to also explore the hollow back idea (from mid-limb out), and the hollow limb idea (from mid-limb in), and of course the idea of utilizing a "natural belly" (high surface density) bamboo for the belly.
Thanks for posting the pics of your bow with some detail. As like Ed, I am curious how much hollow you filled with the cotton matrix? What do you think is the original diameter of your bamboo? and how wide is the bow at present?
You are using judicious applications of sinew to tiller the shape of the reflex? Have you helped to shape it in any mechanical way? What do you think of the idea of twisting the sinew before gluing? Controlling tension was reported "to be the most difficult part of the operation"?
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Hey, thanks for posting the pics, Tim, I had had trouble visualizing how much, how thick, the cotton was and hadn't gotten to paleoplanet.net to check the pic. (My work computers hate that site.)
I was envisioning that wrong, in fact. I was envisioning a more flat, plank-like belly and an actual cotton spacer.
Edit: OK, I actually see that I was essentially correct the second time. The bamboo IS from a large diameter piece, the hollow IS filled, but cotton rises yet a bit above that.
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BowEd:
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" I see.Good picture.Filling concavity of bamboo with cotton.Then sinewing over that."
Yes, the concavity was filled with cotton-glue but also rising well above level, elevating the sinew, the main mass of the sinew high up. The next version will be flat oak, slightly trapped spacer, rectangular section sinew.
willie:
The bamboo's original diameter was 5 inches. There's up to 11" diameter versions but have not found a source as yet.
It would be making grooved roller bridges just to be able to enact your compound-shooters scenario.
" You are using judicious applications of sinew to tiller the shape of the reflex?"
Only to do fine tuning of the tiller, since the bamboo belly can't be touches.
" Have you helped to shape it in any mechanical way?..."
Just the original holding the bamboo in reflex while sinewed.
"What do you think of the idea of twisting and pretensioning the sinew before gluing? It was reported "to be the most difficult part of the operation"?'
I think a rectangular section is most efficient, and twisting introduces energy-wasting give to some extent. But argue back.
Springbuck:
Yes, the first version was quick and dirty. The next will have rectangular sinew.
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I'm a bit skeptical about that sinewing account linked to above. Twisting of strands in a composite material is something you'll never hear recommended. Tendons are likely linear for a reason with an already built in elasticity component.
All the pinnacle of sinewing bows had almost obsessively combed straight fibers.
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Willie: "that the bridges need grooves to keep the cable centered, and if the bridges were free to roll, they would also need tracks to run in."
Absolutely, you need grooves in string bridges for centering, or you need lashing. Rolling bridges could have "lips" that hang over the sides, grooves, or tracks.
One thing I liked about the concept of candy-stripe lashing small diameter bamboo was that the twine of the lashing could roll slightly to accomodate the movement of the cable. One thing I DIDN'T like about that, was that it would likely create lots of wear on the lashings and cable, as well.
Tim: "The next version will be flat oak, slightly trapped spacer, rectangular section sinew."
Ok, then, idea here, Tim. Multiple layers of fabric, cotton or linen, could be stacked for the spacer. They could be glued together with just a wipe of wood glue or thick hide glue. The crossed weave of the fabric would give SOME additional innate integrity. If cut from fabric in DIAGONAL, rather than lengthwise strips, they would contribute NO stiffness to the backing or spacer.
Tim: "Only to do fine tuning of the tiller, since the bamboo belly can't be touches." THIS is one of the advantages of the rectangular or trapped cross section, for sure. Good ol' side tillering.
Tim: Re: "What do you think of the idea of twisting and pre-tensioning the sinew before gluing? It was reported "to be the most difficult part of the operation"?
"I think a rectangular section is most efficient, and twisting introduces energy-wasting give to some extent. But argue back."
I think the most efficient cross section is the one that contributes the least weight AND takes the least set. I THINK you are correct about rectangle cross sections when dealing with wood, but I'm not totally sure, since both trapped and crowned limbs work very well for me.
I will point you in the direction of a bamboo specie called "tre gai" which is smaller diameter, but is enormously dense and has thick walls, and is much harder to split than moso or Taiwan bamboo. A 2" diameter piece will have a hollow middle only about 1/2", but the most dense portion near the surface will be more than 3/8" thick and SOLID. I tried to break a 3' test piece by whacking it on an anvil made from a chunk of railroad track. It broke......eventually, but I could barely dent it at first.
As you know, when using sinew, we have the unique ability to relieve belly stress. A flat belly may be best, but a crowned belly may not be the disaster it is with a wood backing, say.
As far as cables are concerned, there are ways around twisting to pre-tension. Working from forced reflex rather than twisting, having two or more counter-twisted cables, multiple smaller cables running parallel, etc.
Finally, question. What are you doing toward the tips? Does the cotton peter out in thickness? Are you binding down the three layers together, or adding more glue to really secure the whole thing at the tips? Or is it just the same sandwich with exposed layers all the way to the ends?
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I'm a bit skeptical about that sinewing account linked to above.
from wikipedia
Otis Tufton Mason, Ph.D., LL.D. (April 10, 1838 – November 5, 1908) was an American ethnologist and Smithsonian Institution curator.
We know him better as the author of North American Bows Arrows and Quivers. He cites "Ray" as his source.
Twisting the sinew into small bundles, letting them dry some, then sticking down with a glue ball and binding with twine seems like a way to control the tension in different parts of the back, perhaps varying the shrinkage and resulting reflex to create the reflex profile desired? A little different maybe than how Tim is tillering with sinew? And a different design than the "pinnacle" bow with straight fibers, if Pat is referring to a Turkish or other eastern bow.
As an ethnologist, Mason seems to have comparatively studied reports from different expeditions. If this is the case here, the account would be twice removed from the bowyer, and be made by someone who may have never made a bow.
As an alternative to being skeptical, I would rather bring my insights as a bowyer to parse possibly blurry facts, in order to gain understanding about methods I can only hope to duplicate. btw, can anyone point to an original Hupa or Klamath bow? the illustrations shows a rather straight back with flipped tips. If there was natural drying induced "reflex", the bowyer possibly started the sinew application with a deflexed stave.
I did find a report from a P H Ray expedition dated 1884. 700+ pages. Maybe there are some additional worthwhile observations inside.
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Why not curl the bamboo up like a Korean Bow before sinewing?
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I'm a bit skeptical about that sinewing account linked to above.
from wikipedia
Otis Tufton Mason, Ph.D., LL.D. (April 10, 1838 – November 5, 1908) was an American ethnologist and Smithsonian Institution curator.
We know him better as the author of North American Bows Arrows and Quivers. He cites "Ray" as his source.
Twisting the sinew into small bundles, letting them dry some, then sticking down with a glue ball and binding with twine seems like a way to control the tension in different parts of the back, perhaps varying the shrinkage and resulting reflex to create the reflex profile desired? A little different maybe than how Tim is tillering with sinew? And a different design than the "pinnacle" bow with straight fibers, if Pat is referring to a Turkish or other eastern bow.
As an ethnologist, Mason seems to have comparatively studied reports from different expeditions. If this is the case here, the account would be twice removed from the bowyer, and be made by someone who may have never made a bow.
As an alternative to being skeptical, I would rather bring my insights as a bowyer to parse possibly blurry facts, in order to gain understanding about methods I can only hope to duplicate. btw, can anyone point to an original Hupa or Klamath bow? the illustrations shows a rather flat back with flipped tips. If there was natural drying induced "reflex", the bowyer possibly started the sinew application with a deflexed stave.
I did find a report from a P H Ray expedition dated 1884. 700+ pages. Maybe there are some additional worthwhile observations inside.
You can see a Hupa bow in Pope's Study of Bows and Arrows.
Bows tend to work on the same principle so a Hupa bow and a Turkish bow have a lot more in common than not.
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Rolling bridges could have "lips" that hang over the sides, grooves, or tracks.
or maybe just a marble sized to fit inside the bamboo with a short groove on top >:D
there are lots of cool ideas waiting to be tried, but one can only build so many bows.
Why not curl the bamboo up like a Korean Bow before sinewing?
curl up in which direction?
found this, but no side profile
https://www.archerylibrary.com/books/pope/a-study-of-bows-and-arrows/docs/plate04.html
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I'm a bit skeptical about that sinewing account linked to above. Twisting of strands in a composite material is something you'll never hear recommended. Tendons are likely linear for a reason with an already built in elasticity component.
Might be true, but wood is made of molecular chains that twist around each other. Those bundles twist around each other, etc.
This is different from grain, micro-level stuff. Just as an aside.
But, I definitely think longitudinal sinew would be better than twisted, though. You need a lot more mass to get the same resistance. It'll stretch farther as a cord, since we have to stretch the sinew pretty darn far to get the most out of it,that doesn't help us.
The cables BEST application is the other stuff won't work.
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"What do you think of the idea of twisting and pretensioning the sinew before gluing? It was reported "to be the most difficult part of the operation"?'
I think a rectangular section is most efficient, and twisting introduces energy-wasting give to some extent. But argue back.
In retrospect, I think I got the pretensioning (the bundle) idea a bit wrong on the first reading.
Is "energy wasting" the same as "not getting it's full potential?" It does seem like the Hupa bow is not all that reflexed, Why? is there something going on with manipulating drying tensions? Perhaps something similar to how you suspect a core that has some give in the right places could be advantageous? I cant prove it, but I suspect that stretching something as far as it is capable of being stretched, just because it can, may not always be the best application of the materiel, at least when the goal is avoiding hysteresis.
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"Hupa bow (pl. 4, fig. 15). A typical California Indian bow, made of a good quality of yew, broad and flat in the limbs, heavily backed with sinew, and having nocks formed of overlapping and circular bands of the same material. It is strongly reflexed. The handgrip is of buckskin thong bound about the center. It is painted red and blue in a checkered design over the back. Length, 47 inches; diameters: below handgrip, 1˝ by ˝ inches, circumference, 3ľ inches; at mid-limb, 2Ľ by ⅜, circumference, 4ľ inches; at tips, ⅞ by 7/16, circumference 2 inches. The string is very smoothly twisted sinew resembling a cello string, having a formed loop at the top, and made fast at the lower nock by slipknots. A bit of cotton string extends from the loop to the upper nock. When braced this bow is very musical, has a soft, even draw, and weighs 40 pounds; drawn 22 inches, it shoots 148 yards. In action it bends in the center and consequently kicks in the hand. It would seem to be a good bow for small game"
From Pope's book
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willie / Springbuck:
"Rolling bridges" wouldn't exactly roll; they'd only have to roll some small part of an inch. To test if rolling or toggling bridges would be more efficient [by reducing friction against stationary bridges] short lengths of wood pole, of the same diameter as bridge height, could be set temporarily under the backing just long enough for a test, the regular bridges removed for the test. When braced, the downward force of the backing would hold the rolling test bridges in place long enough for testing.
Springbuck:
Your fabric spacer idea is worth serious thought. Likely some configuration of different fabrics and glue will do the job, so it's now a serious candidate. Thanks, even though I hate it that you thought of it first. For me at least, every part of the bow must be paleo-legal: could reasonably have been made before the metal ages, and woven fabric was around a few thousand years before the copper age.
" What are you doing toward the tips? Does the cotton peter out in thickness? Are you binding down the three layers together, or adding more glue to really secure the whole thing at the tips? Or is it just the same sandwich with exposed layers all the way to the ends?"
For this first test version the cotton and sinew taper somewhat in thickness from working grip to near tips. Much of the tiller comes from the largely pyramid front view. On future versions the spacer and backing will taper to zero a few or many or many many inches from the nocks, narrow wood beyond that, for low outer limb mass.
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The cotton in place
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Maybe a better sense of how it rises above the bamboo ridges:
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Second try
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With two ounces of sinew:
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Lots of open spaces in the cotton layer, so possibly lighter that a wood spacer. This sparsity of glue worried me that it might not hold together even through the drying process, so wrapped it tightly. Same for the sinew. Both held together though once dry, wrapping removed, then braced and drawn.
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Do you have a moisture protection plan for this bow going to Mojam?
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PatM:
For the first mojam my bows arrived in a plastic container; they weren't taken out till the day we did the tests. Probably a good plan for this bow too. Hard to believe that was almost 20 years ago.
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Tim, It would be really nice if you could accompany Steve to MoJam this year for the anniversary and flight shoot... :) :OK
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willie: "Twisting the sinew into small bundles, letting them dry some, then sticking down with a glue ball and binding with twine seems like a way to control the tension in different parts of the back, perhaps varying the shrinkage and resulting reflex to create the reflex profile desired?"
Willie, I think it could do any or all of the above, but I just recently worked with sinew for about the 4th time ever, and I have a thought on that. I was helping a guy repair a lifted back on a Miwok bow, and learned all over how hard it is to handle sinew. I see lots of guys combing it out in little bundles, even tying similar-sized bundles together, etc.
"The most difficult part of the operation...." from the article. It's one thing to say a Klamath bow had several courses of sinew on the back and another to understand how the hell the guy did it without sinew stuck to everything he owned and made the bow anything other than butt ugly.
Maybe this account of the Native guy twisting sinew into bundles wasn't to imprve performance, etc.. perhaps simply a way to make them easier to handle.
Sinew strands get everywhere, stick to everything, half the bundle goes on the bow, half stays on your hand. If you are grabbing bundles out of a bag or out of a bunch you always have too few or too many, or too long or short, etc.... ..... So, like, maybe gather similar-sized bundles, add a little glue, twist em up till they stick together and lay them aside. An 8" bundle has maybe one and a half or two rotations, tips tapering out to rat-tails, nothing like a double reverse twisted two ply sting or anything.
When you have enough, size the back of the bow and lay the now tacky bundles on, adding glue as needed.
Conjecture, but method is important. Devil is in the details.
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PatM said: " Why not curl the bamboo up like a Korean Bow before sinewing?"
I guess I was assuming that was next.... ;D :P Knowing what I know about Tim.
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Sinew doesn't HAVE to be that finicky to work with.
The comment about curling the bamboo up was a bit of a trick question. ;)
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PatM said: " Why not curl the bamboo up like a Korean Bow before sinewing?"
I guess I was assuming that was next.... ;D :P Knowing what I know about Tim.
I want to know the maximum bend bamboo can take before compression failure. Of course, that has too many variables, so is there a standard chart that has compression limits for wood?
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willie: "Is "energy wasting" the same as "not getting it's full potential?"
I kind of think it is. I, like you, don't think it is a good idea to stretch things right to the limit, but.......
I'm pulling some numbers out of the air, here, but..... Say we want a sinew back for a 50 lb bow. Since sinew can stretch almost 10% of its length, you can take "X" amount of sinew and pull it 8% of its length to get the 50 lbs. OR, you can take "2X" amount of sinew and stretch it 4% of it's length. Something like that.
Sinew is heavier than wood.
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It's also generally said that sinew works best with woods like Juniper but wouldn't exceptionally stiff wood force sinew to stretch more?
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SpringBuck:
I don't know if you're using a similar method or not, so just in case:
If all the sinew needed for a bow is worked into bundles, then all of the bundles trolled through water till soft and all strands parallel, then you won't be working with raggedy dry sinew which wants to stick to your hands and make life miserable. Sinewing is a breeze when the the bundles are prepared in damp bundles. Such prepared bundles can also be allowed to dry for future use, a quick water bath making them ready to go. When like this you can begin sinewing at a moments notice:
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PatM:
" ...wouldn't exceptionally stiff wood force sinew to stretch more?"
All else equal, stiffer wood = thinner limbs, so the sinew is resting closer to the neutral plane, so it's actually stretching less. One reason sinew works so well on Juniper is because, all else equal, bow limbs of it are thicker
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Tim, kind of like that. As I said, I'm new to sinew, so this isn't "how I was doing it", but look at your bundles. Just regarding the twisting technique mentioned.
If each of those "sub-bundles" in the larger, tied bundles were made up like that; about that size, damp, and just a little glue, then each given a single full twist to roll them together, they would hold themselves. You could lay them aside and let them dry a bit, sort for size, etc.
That's all.
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But does the lower bend resistance not counter that?
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It would seem that bend resistance would be equal in same draw weight limbs. Thicker wood raising the sinew farther above the center of the bow limb causing a longer stretch of the back and sinew. I hope I'm following Tim correctly anyway
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Springbuck:
That would be a quicker and easier way to make a cable, and allow less twisting, another plus. A couple of tries needed to get the variables right. Shouldn't take long.
PatM:
The lower bend resistance means thicker wood is needed for a given draw weight. Juniper's high elasticity allows this. It's likley the best wood/sinew combination of all. Yew might be second.
Yellarwood:
That's right. The naturally elevated sinew on a Juniper limb is a smaller natural version of the elevated sinew test bow here.
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Tim, not following. Which would be an easier way to make a cable?
What I'm describing would be for backing, and is just a hypothesis.
Each of your minor bundles looks like it was wet and just stroked parallel to smooth them together. I was thinking that, alternatively, under primitive conditions, each small bundle could be twisted together, but not for coiling, counter-twisting, or making cable. Just twisted up lightly for ease of handling, rather than tightly twisted for cable. Almost parallel, nothing like cord. When applied, loose enough to still be smoothed and blended.
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Tim: "Thanks, even though I hate it that you thought of it first."
Just doing what Tiggers do best. I have such a serious case of ADD, that I can't even think in the box when I try. This kind of brainstorming is one of my favorite things to do. ;D Remind me to show you my list of things I need to patent, but lost interest in once I had a working prototype.
Nice to be able to put it to use.
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It's also generally said that sinew works best with woods like Juniper but wouldn't exceptionally stiff wood force sinew to stretch more?
All else equal, stiffer wood = thinner limbs, so the sinew is resting closer to the neutral plane, so it's actually stretching less. One reason sinew But does the lower bend resistance not counter that?works so well on Juniper is because, all else equal, bow limbs of it are thicker
But does the lower bend resistance not counter that?
The lower bend resistance means thicker wood is needed for a given draw weight. Juniper's high elasticity allows this.
The principles being cited on both sides of this discussion are correct. To know which ones are more correct, one would have to run the numbers for a specific combo. It is actually not that hard. if someone wants to sketch an specific example. (Please keep it rectangular) I can show the calc.
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willie: "Is "energy wasting" the same as "not getting it's full potential?"
I kind of think it is. I, like you, don't think it is a good idea to stretch things right to the limit, but.......
I'm pulling some numbers out of the air, here, but..... Say we want a sinew back for a 50 lb bow. Since sinew can stretch almost 10% of its length, you can take "X" amount of sinew and pull it 8% of its length to get the 50 lbs. OR, you can take "2X" amount of sinew and stretch it 4% of it's length. Something like that.
Sinew is heavier than wood.
Two possibilities, say 2% and 4%, not near max.
I propose that the 2% has less unit hysteresis than the 4%, that is per sample of the materiel compared to an otherwise equal sample of the same materiel. When incorporated into a limb, it is a trade off. the more efficient 2% sinew is not as thick (less weight) for a double advantage, but in order to make a short limbed (and much lighter weight core/belly) bow bend enough to have a good powerstroke, the sinew needs to be proportionally thicker in the crossection. There is probably a different "sweet spot " percentage depending on the length of the bow.
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Bob Barnes:
" Tim, It would be really nice if you could accompany Steve to MoJam this year for the anniversary and flight shoot... "
Thanks for that, and if the anniversary meet was set up like the original meet I'd love to be there. At the first meet full and precise bow stats were taken and bows accurately chronographed. Much of value was learned. The coming meet is a different animal altogether. Its rules could see an excellent design have a poor showing, a fair bow getting greater distance. More misinformation could come from this meet than information. Bowmakers value solid design information, and participants at the first meet very much enjoyed putting their bows through the process. Everyone benefited, primitive archery especially. Maybe next year.
Springbuck:
Somehow I got the idea you were talking about cable making. 10 points off for me.
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We'll test your bow anyway at Mo Jam.
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Bob Barnes:
" Tim, It would be really nice if you could accompany Steve to MoJam this year for the anniversary and flight shoot... "
Thanks for that, and if the anniversary meet was set up like the original meet I'd love to be there. At the first meet full and precise bow stats were taken and bows accurately chronographed. Much of value was learned. The coming meet is a different animal altogether. Its rules could see an excellent design have a poor showing, a fair bow getting greater distance. More misinformation could come from this meet than information. Bowmakers value solid design information, and participants at the first meet very much enjoyed putting their bows through the process. Everyone benefited, primitive archery especially. Maybe next year.
Well that's pessimistic. It's just as likely to be the opposite. Regardless, it will be a learning experience whichever way it goes
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Well, i think what has been learned over the years is being put into the rules for this shoot. We should come up with much more accurate results this time. I do want us to do the chrono shoot as well though.
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Sleek, our spread sheet has a place for the fps readings as well. One can shoot both the chrono and the flight shoot or either one of the two. They are both optional.
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I started not to reply on this post about sinew... but since I have put sinew on 2 bows in the past week and will be sinewing another one in a day or two, I decided it's OK. :) I totally agree that the new flight shoot rules will give us very credible information and have no doubt about the validity of the information that we will gather. It will be added as just another chapter in our modern progression of this wood bow passion.
Back to sinew... I am drying a 60" reflexed rocky mountain juniper and a highly delfexed/reflexed 64" osage...and will be putting some sinew on a 58" american elm with slightly reflexed tips in a day or two. I know the rule is not to sinew a 64" osage longbow, but mine was a very low density/light mass weight osage stave as well as my first bow off a new highly D/R caul. I just want to see what it will do as is, but can shorten it later if I feel a need to do so.
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Sleek, our spread sheet has a place for the fps readings as well. One can shoot both the chrono and the flight shoot or either one of the two. They are both optional.
Oh, sweet. Then im happy :)
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Say, with this effort to document and test, are we lookong at the potential of another TBB, Volume V? Maybe it could address all the old outdated dogma and correct it with what we have learned since the first 4 volumes, why and how the nee material was learned, and of course include as much as can be put in there about new knowledge, and ways of looking at familiar problems, this thread for example,
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More misinformation could come from this meet than information. Bowmakers value solid design information
OK, but if you are talking about the broadhead flight event, isn't the focus with that just to have fun shooting for distance?
Maybe next year.
what kind of challenge would you like to see or sponsor next year?
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BowEd:
" We'll test your bow anyway at Mo Jam."
I'd send a bow or two if real testing was planned. At present it's like a foot race where all the runners start at randomly different times, no way of knowing the actual performance of each. Variables have to be eliminated for sound results. As presently set up the meet could generate more misinformation than fact.
Willie:
" ... isn't the focus with that just to have fun shooting for distance? "
A bow meet is worth doing just for that. What a great opportunity though to gather solid knowledge.
" what kind of challenge would you like to see or sponsor next year? "
Essentially the same test procedures as at the first meet. One essential feature being that all bows be chronographed by the same shooter [or pair of same fps shooters as at the thirst meet] each shot well witnessed by critical eyes.
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" what kind of challenge would you like to see or sponsor next year? "
Essentially the same test procedures as at the first meet. One essential feature being that all bows be chronographed by the same shooter [or pair of same fps shooters as at the thirst meet] each shot well witnessed by critical eyes.
Sounds somewhat like a disparaging assumption.
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Are you referring to the broadhead flightshoot?
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We tried to make it a better comparison by having all bows shoot arrows that are 10 grains per pound of the bow's 28" draw weight. Everything will be measured by at least 2 different devices and there will be several officials on hand to witness every shot. It seems to make more sense that every bow shooting the same 500 grain arrow regardless of the draw weight of the bow. We build lots of bows at MoJam and this was designed as a way to fairly compare the different bow designs, woods, and workmanship. We all love watching arrows fly long distances and we will all enjoy watching the shooters do their best to exceed their best previous shots.
Sinew update- I managed to prep about 3 ounces of back sinew for the little elm bow... :OK
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Flight shooting is an ancient sport that was developed for exactly the same reasons we are doing it. Trends will develop over time if the program is successful and trends always say more than small samples. For some reason I have always enjoyed watching arrows fly more than I have shooting through a chrono. It is a double bonus when you have both.
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I still say the draw length limit was a needless hobbling of the potential of bows.
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now this thread has taken a definite side turn... :) but I have done lots of testing with bows using different draw lengths and it seems that there is a definite advantage to a longer draw length... as in a 50#@30 has an advantage over a bow drawing 50#@26... by having the 'official' shot taken at the same (measured) draw length it seems the most fair way to compare the bows.... ???
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That's what I think is irrelevant. Bows aren't designed to all be the same.
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Pat, in this contest they are. They can draw shorter if they like. Just not longer.
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I know and that's why my view is the same as Tim's.
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well AMO is measured by shooting 9 grains per pound at @30" and IBO is measured by shooting 5 grains per pound at 30" so why would we not use something closer to our standard by shooting 10 grains per pound @28" ? I'm trying to understand , not argue...
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I think it should be a contest to see which type of bow shoots a broadhead arrow the farthest distance. If that's a long draw bow, so be it.
Back in the day they found out that tiny bows shot tiny arrows farther. In don't think anyone said that was silly and unpractical and that everyone should shoot normal length bows and arrows instead.
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we are only using the broadhead, mounted at 28", as an arrow stop so that the arrow can only be drawn to 28"...
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We all get that part. That's the argument.
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I think it should be a contest to see which type of bow shoots a broadhead arrow the farthest distance. If that's a long draw bow, so be it.
Back in the day they found out that tiny bows shot tiny arrows farther. In don't think anyone said that was silly and unpractical and that everyone should shoot normal length bows and arrows instead.
Pat you are completely missing the point of the whole thing either that or you just want to argue. Debate on the draw length is over. The vast majority of primitive bows are built at 28" or less draw. This is who the primary target audience is for this shoot.
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I'm well aware of the in crowd decision. I am merely voicing my opinion as we are still allowed to do.
There never really was a draw length debate. Let's be honest here.
Thr idea that it's a " primitve" contest with grains per pound and draw length limits using a standard steel broadhead is amusing though. ;)
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my 'broadheads' are actually trade points...so it's OK... (lol)
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Trade points sure ain't primitive.
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MoJam rules makers:
Here's a thought for future meets, or this one if it's not too late: The first Mo Meet's bow testing occupied just a few hours of total meet time, and only those wishing to participating. A fun gathering of bow folks for casual shooting isn't incompatible with also setting a few hours aside for precise stat taking and precise chronographing, only those interested in such participating. One would not interfere with the other, instead making the meet more enjoyable. Is it too late add this feature to the coming meet? This is a unique opportunity to enlarge the store of primitive archery knowledge. Is there any good reason not to do this?
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I have an issue with the 10 grains per pound and feel if this were fixed, all draw length questions would be answered.
I wrote this back in 2012 and i still feel this way. If I can make Any contribution to archery, i want this to be it.
I would like to express an opinion based of things I understand to be true and things I have read that others believe to be true. I am asking only to raise more questions, not present facts.
I think that the idea of shooting a 10 grain per pound arrow is a bad one. I think it can be misleading and overload or underload a bow depending on the bows powerstroke ( draw length minus brace heigth ). My point is bassed off stored energy. To start off with an example, I will use the cross bow. A cross bow may have a 14 inch draw and a 200 lb draw weight. ( not listing numers from any specific bow, just numbers that could be. ) If this bow were to shoot a 10 gpp ( grain per pound ) arrow it would fire a 2000 grain arrow. That arrow would fly about as far as a brick.
What is the reason for this? I feel the first answer is so obvious you would wonder at my question, but the answer is more detailed than the obvious " the arrow is too heavy " answer one would be likely to spurt out at first thought. I would be more inclined to say that the poor flight of an arrow 2000 grains out of a 200 lb @ 14 inches bow could be blamed on the arrow not being correct to the ratio of power stroke to draw length. The distance a bow is pulled in combination with the weight it reaches ( see note below ) will determine how much energy the bow stores. In this argument assume a well built bow with low tip mass, set, ect... This energy storage is all the bow has to offer to the arrow.
If you always make the arrow 10gpp, the shorter power stroke bow will suffer because of the reduced energy presented to it compared to that of a longer powerstroke bow. I would venture so far as to say that a 50 lb @ 15 with 10 gpp would perform less in arrow flight than would a 30lb @ 30 inches with a 500 grain arrow from the 50 lb bow. ( I havent done the math, but I used the numbers to illustrate my point. )
There must be a ratio of energy storage of the bow to grains per pound of arrow mass. The idea of having a standard by which to measure a bows performance is good and needed, but I think I have shown why I think 10 gpp is a bad way to measure performance of a bow, just as bad and flawed in the same way as ( those who have read the TBB series will remember this one ) measuring all bows performance with a 500 grain arrow regardless to poundage or draw length. These two factors must be calculated into measuring a bows performance. And since it is draw weight and length the bow offers ( potential energy ) and weight of the arrow I think a ratio should be calculated and used to determine the effeciency of a bow based on draw length, weight and arrow weight.
As an additional thought to this topic, I think there is a maximun effecient draw length for every draw weight of bow and that will depend on the arrow weight chosen. Shorter draw lengths get lighter arrows, longer draws get heavier. But again, here I say there is a ratio.
( Ref. note above )
The end poundage of a bow does not matter as much to the kenetic energy of an arrow as does what the force draw ( FD ) curve looks like. High energy storage in a bows early stages of draw gives the arrow the benifit of the rest of the draw length to absorb that energy. The longer the arrow is inside the fat of of the FD curve, the happier it is, as an arrow can soak up energy as fast as it is given. The more energyin the FD curve that is ahead of the arrow ( read early draw weight ), the more it leaves the bow with. This was not exactly part of my original discussion but felt it played a significant part of the performance of a bow and needed to be understood by people who havent read about fd curves yet.
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After presenting my argument, Dave, aka woodbear, came up with this simple formula and I believe its the one that should always be used.
10gpp x draw/28
This little gem can normalize any draw length and put every bow on an even playing field by adjusting the arrow weight to the bkws draw weight AND draw length. I bring this up every chance i get. I feel like if this oportunity to adopt this formula as a standard is wasted, progress will NEVER be made.
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Sleek
So according to your proposal, someone that has a 26" or 30" to back of broadhead arrow, should be allowed to shoot no lighter than 26 x 500 / 28 = 464 gr arrow, and 30 x 500 / 28 = 536 gr arrow ?
I suppose what we need know from Badger, is whether the purpose of the event is to create a competition that pretty much duplicates the competitive focus of the existing USAA Broadhead event or whether he sees something with less rules and classes that might have a broader appeal as a club shoot.
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MoJam rules makers:
Here's a thought for future meets, or this one if it's not too late: The first Mo Meet's bow testing occupied just a few hours of total meet time, and only those wishing to participating. A fun gathering of bow folks for casual shooting isn't incompatible with also setting a few hours aside for precise stat taking and precise chronographing, only those interested in such participating. One would not interfere with the other, instead making the meet more enjoyable. Is it too late add this feature to the coming meet? This is a unique opportunity to enlarge the store of primitive archery knowledge. Is there any good reason not to do this?
Tim, the spreadsheet and entry form has a place for FPS, a chrono will be available to shoot though but the archer will have to shoot it himself. My personal goal is to promote a flight shoot but I support gathering the info off the chrono. I do agree that without one person doing all the shooting or using a shooting machine the data is of limited value and that is one of the reasons I am not pushing it.
Sleek, a standard has to be used in testing primitive has adopted a standard of 10 grains at 28". If the archer chooses to short draw we can't make adjustments for that. A cross bow with a shorter draw would indeed not use a 10 grain standard he would work off stored energy as you suggested. The 10 grains is based on a 28" draw, if the bow stores less energy at 28" it simply pays the penalty.
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MoJam rules makers:
Here's a thought for future meets, or this one if it's not too late: The first Mo Meet's bow testing occupied just a few hours of total meet time, and only those wishing to participating. A fun gathering of bow folks for casual shooting isn't incompatible with also setting a few hours aside for precise stat taking and precise chronographing, only those interested in such participating. One would not interfere with the other, instead making the meet more enjoyable. Is it too late add this feature to the coming meet? This is a unique opportunity to enlarge the store of primitive archery knowledge. Is there any good reason not to do this?
Tim, the spreadsheet and entry form has a place for FPS, a chrono will be available to shoot though but the archer will have to shoot it himself. My personal goal is to promote a flight shoot but I support gathering the info off the chrono. I do agree that without one person doing all the shooting or using a shooting machine the data is of limited value and that is one of the reasons I am not pushing it.
Sleek, a standard has to be used in testing primitive has adopted a standard of 10 grains at 28". If the archer chooses to short draw we can't make adjustments for that. A cross bow with a shorter draw would indeed not use a 10 grain standard he would work off stored energy as you suggested. The 10 grains is based on a 28" draw, if the bow stores less energy at 28" it simply pays the penalty.
I respect you a lot. In this case i have to very much disagree. The standard is wrong. Here we have a chance to fix it. To just shrug and say oh well to this is not inline with progressing archery. If we say we hope to learn things and advance, how can we if we ignore certain facts, and important ones. Simple as thelis solution is to a few problems that have been discussed already, and the ease we can implement this, only to be shrugged off, is hard to just deal with.
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This is a competition the way I see it.The bow/the shooter/and his arrow as a team against other teams.For those who participate it'll be a learning experience.For those who don't it won't.
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We have already hijacked Tim's thread but for the record I have no desire to change it. I do use the method Sleek is suggesting when I am testing light arrow flight bows but for this we need a basic standard. In regular flight shooting all bows shoot 450 grains even if they draw 100#. Here we simply set a different standard using hunting weight arrows. This is a hunters round.
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I can appreciate that myself.
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Badger, how many fps difference will 36 grains make? Thats the difference between 26 and 28 inches draw at 50 pounds. 50 grains difference at 70 pounds. For war bows, the difference is huge, 108 grains difference in just 2 inches of draw for a 150 pound bow.
Now let me ask this, as it is set up, what is the grain tollerance on an arrow? Say you have a 50 pound bow and have an arrow that weighs 464. Would that be allowed?
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We have already hijacked Tim's thread but for the record I have no desire to change it. I do use the method Sleek is suggesting when I am testing light arrow flight bows but for this we need a basic standard. In regular flight shooting all bows shoot 450 grains even if they draw 100#. Here we simply set a different standard using hunting weight arrows. This is a hunters round.
Fine, i will move to another thread.
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Badger:
How about this: The meet proceeds as presently contemplated, then one afternoon those who are interested in doing so, set up a test spot where full stats will be taken and bows precisely chronographed. No effort needed on you guy's part, except maybe to announce that this feature will exist. We'd bring the needed scales, arrows, chronographs, etc. If ok I'll start on a tentative stats list and test standards, based on the first meet's testing. Is there any reason not to do this?
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At the first Pope and Young meet back in the 30s Chet Stevenson used a 90 pound plus static to shoot a broadhead around 325 yards. Chet was a hunter.
I want to see that, not a potato sack footrace.
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Pat, that how the regular flight league is set up. You will be seeing plenty of broadhead shots over 300 yards in the future because they are shooting 450 grain arrows. I am quite certain you will be seeing 70 # bows hit the 300 mark. We are using a hunters standard of 10 grains per pound. If you find that boring I suggest you don't attend.
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Tim, this is already happening, instead of the 100 plus bow weight standard it is switched to 10 grains per pound, they are actually very similar but 70# bow will be much less efficient and 35# bow will be more efficient using the 100 plus bow weight measure. The only thing we don't have is designated shooters. I am so busy getting this together I don't have time for anything else. We are currently weighing mass, bow length, and recording material and construction. We will be using a top grade scale and the spread sheet is already equipped to handle this info. To be honest my main interest in the speed was so that I could compare speeds to distances, so from my standpoint I wanted to see the same archers shoot through the chrono as shooting on the flight field. This would give other archers a better idea about potential. The current crop of bow builders has gotten so good I doubt you will see much more improvement using standard designs.
Badger:
How about this: The meet proceeds as presently contemplated, then one afternoon those who are interested in doing so, set up a test spot where full stats will be taken and bows precisely chronographed. No effort needed on you guy's part, except maybe to announce that this feature will exist. We'd bring the needed scales, arrows, chronographs, etc. If ok I'll start on a tentative stats list and test standards, based on the first meet's testing. Is there any reason not to do this?
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Badger:
"I am so busy getting this together I don't have time for anything else."
I can imagine. So just these parting words on the subject and I'll quit pestering you on line here. I can do a better job of pestering you in person here in L.A.
I'm starting to feel semi rude trying to crash you're party with a smaller party. So I and interested others will try to set up our own party in the future, so we can take stats to our heart's content.
So this is me butting out.
All: Yes, Badger/Steve and I are disagreeing about the value of the proposed stat taking. But despite appearance, Steve and I are close friends, but do continually argue about bow design, so much so, and this in no exaggeration, that 9 times out of 10, when we happen to be driving to some bow related location, argument will begin almost immediately, and become so engrossing that we miss the first turn, the argument resuming while searching the for the turn, such that half the time we miss the second turn too. Apparently one of us argues too much.
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Man, i hate it when parents fight....
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Tim,
My invitation to MoJam still stands and if you wanted to set something up, Keith would be more than willing to add it to the schedule...there is plenty of time for it there. I can see the interest in speed testing and I'm thinking most of the shooters would like to know how fast their bows shoot. We will have a chronograph there, and I can bring mine if needed...
Sleek,
It would be nice if you could attend as well. The idea of using a formula is interesting as well. I would love to plug my friend John Murray's to your 10gpp x draw/28 formula. John shoots a 130# ELB and his arrows have hammer forged bodkin points. I would venture to say that if he followed your formula we would run out of room on our 300 yard long course.
As someone that has been to almost every MoJam and considers myself part of the family there, I invite everyone that shares this passion for making bows and watching arrows fly!
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Bob, I have EVERY intention of being there. I have been once. Your friends reputaion with that long bow precedes him, I have heard a lot about him.
I want to stress, i did not make that formula, I just said it needed to exist. Dave, Aka Woodbear, from paleoplanet came up with it.
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Bob Barnes:
Keith is still the guy? That's pleasant news. 20 years ago, when I challenged the old Leatherwall anti whitewood folks to a shootout, Keith jumped in and offered to host the meet. Might never have happened without him. I've got an ancient e-address of his. I'll contact him and see what we can do. Thanks for paving the way.
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Badger:
"I am so busy getting this together I don't have time for anything else."
I can imagine. So just these parting words on the subject and I'll quit pestering you on line here. I can do a better job of pestering you in person here in L.A.
I'm starting to feel semi rude trying to crash you're party with a smaller party. So I and interested others will try to set up our own party in the future, so we can take stats to our heart's content.
So this is me butting out.
All: Yes, Badger/Steve and I are disagreeing about the value of the proposed stat taking. But despite appearance, Steve and I are close friends, but do continually argue about bow design, so much so, and this in no exaggeration, that 9 times out of 10, when we happen to be driving to some bow related location, argument will begin almost immediately, and become so engrossing that we miss the first turn, the argument resuming while searching the for the turn, such that half the time we miss the second turn too. Apparently one of us argues too much.
Tim, do you favor the old method of a 500 grain arrow for everyone and using bow weight plus 100 or do you favor a grains per pound method? Sleeks method might be a good updated version to think about for a testing event.
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I have high hopes for a version of the test elevated sinew bow here, but the bow gods care nothing about high hopes. Several years ago I came up with a wood bow design which had a compound-like FD curve, and raved to several bowmaking friends about it. Shouldn't have. It was slower than a poorly tillered D bow. So present high hopes are on hold. It's pictured here before the outer limbs were pyramid shaped.
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Second try.
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Another:
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one I'm waiting for the sinew to get dry... :OK
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That is interesting tim. Especially that top one. Do you plan on leaving the levers full length? The triangular braces, are they going to stay that bulky?
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Badger:
I'll put together a tentative stat and test list and brainstorm it with you.
Putting the touch-up sinew on that test bow tonight.
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Putting the touch-up sinew on that test bow tonight.
Cool, how long has it been taking sinew to dry when applied in small spots?
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willie:
"... how long has it been taking sinew to dry when applied in small spots?"
Almost as long as for a just-senewed bow. Water from the glue soaks down deep and takes a long time to travel back out.
sleek:
It's the same bow in both photos. They're from 10 years ago. Yes, the outer limbs were kept that long, and did a bit of energy storing; they were tapered to near zero before testing. Despite a very fat FD curve it shot as slow an especially poor D bow. Theory and hope is no match for reality. A bamboo version did as poorly. They were quickly trashed.
Here'a a photo of both, and a 3-point F/D curve for each. Lesson learned: F/D curves can be poor predictors of performance
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The bows
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Tim,
any ideas why they under performed?
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willie:
" any ideas why they under performed?"
One reason is the same for why recurves so often shoot slower than well-made straight bows: Outer limbs store a tiny fraction of total energy while outer limb mass eats up tons of it. Another: The huge % of limb devoted to retroflex put crushing strain where most of the energy is stored and hysteresis is very high in such overstrained wood. It was an anti Mantra bow.
And in the looks department it was an anti Bob Barnes bow--see six posts above.
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Tim, im wondering something and that never goes well, but here goes...
Your goal is to stress the sinew out as much as possible to get gull use of it. But the way they reflex horn bows isnt possible with wood bows because the wood cant handle that much compression ( can it? Is it really being compressed if its stretched first then bent back to normal shape? ). So perhaps you can reflex a woden bow with sinew the way a horn bow would be, then slowly heat the belly ( this works from my experience ) with a heat gun, work the belly with heat, and apply pressure to flatten the limb out. A damp rag to wipe the heat iff the back helps. That would stress that sinew out, but still allow the wooden belly to bend at full draw without failing.
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Sleek:
Elevating the sinew will allow it to be even more strained than on an Asiatic composite, if desired. Reflexing is still important, and the fact that sinew in this design is storing such a high % of total energy means that the belly doesn't have to do much tension work, so it can be much thinner than otherwise. Being so thin it can be pulled into far larger reflex than conventionally. For example, the bow can be tillered backward to full draw then elevated sinew applied. Even though thinner than a conventional belly it's full thickness is free to do the compression work
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A fun and maybe dumb idea: One or more versions of the experiment bow here will be given a poor-man's horn belly:
When a puddle of hide glue is allowed to fully dry it's surprisingly horn-like. If applied in successive coats to a bow belly the bow becomes substantially stiffer. And since hide glue is about as elastic as horn it should be able, like actual horn, to carry much or most of the compression load and store much or most of the compression energy, protecting the wood belly in the process.
If the belly, now core, is an especially light wood, when then pulled into reflex and sinew backed, an especially light and high-stored-energy bow should result.
I'm just starting to play with this. Maybe others would like to also, and report their results. A dumb part of the idea is that hide glue is prey to moisture, so a glue belly would need special protection.
Glue can be brushed on, but only thin coats result, hours of drying time needed so the new coat won't melt the earlier one. One way to speed the process and insure thicker and more uniform coats is to set a mostly-open-space fiber mesh down and saturate it with glue. It's not paleo, but to speed testing, a separated, gossamer thin strip of toilet paper does the job, several now-thicker coats allowed at the same time. The wood fiber is maybe 5% of each layer's mass, does no work itself and prevent no work from being done.
Questions and comments and arguments welcome.
Side view of 1/2” thick redwood bow limb, the thin brushed-on dried glue belly at top.
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Transparent dried glue belly.
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A speedy way to apply the glue is via squeeze bottle, like mustard or ketchup comes in. Keep it in the fridge between sessions. 50 points to the first person to identify that black material beside the bamboo.
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50 points to what?It's bahleen.You can do better than that....lol.Nifty squeeze hide glue bottle.Your hide glue belly is made of cologen though.Horn is keratine.Be interesting to see how much compression it will take though.
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50 points to the first person to identify that black material beside the bamboo.
Salty Liquorice?
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I have seen baleen used as backing, but does it work as a belly?
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Dean Torges made a bow with a baleen belly...I think JD Jones has it now.
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The little Rimankyu bows made by the Japanese are all baleen.
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you might be interested in a range of weights
http://bjornhideglue.com/product-category/regular-clarity/The molecular weight of hide glue has a wide range from 20,000 – 250,000. The higher the gel strength, the higher the molecular weight.
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How many layers of TP, Tim?
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you might be interested in a range of weights
http://bjornhideglue.com/hide-glue-info/The molecular weight of hide glue has a wide range from 20,000 – 250,000. The higher the gel strength, the higher the molecular weight.
Now that is fascinating. How do you create a glue with a higher weight?
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buy it that way, i think it different weights are sort of like distillation, it comes off the top in different "pours" as it the hide or whatever is cooked down.
see if this attachment will open
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Your hide glue belly is made of cologen though.Horn is keratine.Be interesting to see how much compression it will take though.
Ed, I often add Colloidal silica to my glue to make it harder. maybe there is a natural equivalent or something similar?
https://www.westsystem.com/406-colloidal-silica/
maybe the guy that was saving his toenail clippings for a bow belly is still around
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Your hide glue belly is made of cologen though.Horn is keratine.Be interesting to see how much compression it will take though.
Ed, I often add Colloidal silica to my glue to make it harder. maybe there is a natural equivalent or something similar?
https://www.westsystem.com/406-colloidal-silica/
maybe the guy that was saving his toenail clippings for a bow belly is still around
Ew. But, interesting, but ew.
Can human hair be bound with hide glue in such a way as to make a bow belly? My hair is down to my butt. Plenty enough to do that with if I have reasin yo believe it can be done. I will do it.
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Ack there i go again, derailing the thread. Gonna start another
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BowEd:
Yes, it's whale baleen. You win the 50 points, duly recorded. They're fully transferable and can be traded with other point holders or used to make purchases in the paleo economy, paleo bitcoin. Just kidding, but not a bad idea.
sleek:
" I have seen baleen used as backing, but does it work as a belly?
Yes. As belly material it stand about half way between horn and bow wood itself. The Asiatic-style bow on page 87 of TBB-1 used baleen on the belly.
PatM:
The glue belly in the photo on the previous page was brushed on. Maybe ten coats. Three layers of TP/glue yields the same thickness, and much more uniformly. It's best to use cheap, thin, almost see-through versions, and to peel its two layers apart, each layer more air than fiber.
Sleek:
Knox Gelatin, and similar, is surprisingly high-quality glue, with a bloom or gel strength of about 300, just about the highest of any glue.
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Some hide glue info:
The higher the gram strength of hide glue the quicker it gels, often too quickly. One solution is to keep the work, sinew and air at high temperature. Another is to dilute the glue.
Hide glue you make yourself, from sinew scraps or hide scrapings will typically yield about 180 gram strength glue, gels slower for longer working time, and is stronger than needed for about any imaginable need.
Gelatin glue is about 350 gram strength.
How to mix it:
http://www.frets.com/FretsPages/Luthier/TipsTricks/KitchenGlue/kitchenglue.html
Three times water weight to dry glue weight is difficult to mix. Six times is easier.
The lower the water content the quicker a sinewed back or such will dry.
Dry hide glue is about 1.3 specific gravity, twice as heavy as many bow woods.
Tensile strength up to 10,000-plus per square inch.
The lower the moisture content the higher the tensile strength, and vice versa
Can be stretch 5% to 10% of length.
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Excellent info Tim, thank you
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+1.Composites have always fascinated me.They are creatures of a different type when it comes to bows.
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This article, or the one linked to this article, brings up a question for me. I've heard that you need to prepare your surfaces to be glued no more than 3 days before the glueing process to avoid oxidation of the surfaces. Makes sense. But what I want to know is how deep does this oxidation penetrate into the wood surface? How far down does one need to scrape or sand the surface to fully remove the oxidized fibres? Is it just the immediate surface, say a few thousandths of an inch, or does this oxidation travel deeper? Maybe it depends on the amount of time it has been sitting?
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Aaron, I haven't really had much of a problem with oxidation beyond just a light sanding being needed but I have had a problem with the limb cupping and needing to be flattened back out. Mainly on my bamboo I have experienced this but to a lesser degree on osage and other woods. I wonder if light cupping might be misdiagnosed as oxidation?
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I'm not considering myself as an expert here while not a novice either but oxidation is just on the surface IMHO.100 grit is more than rough enough to eliminate oxidized surface.Look at wood darkening over time brought to normal color with a little sanding.Testing shows over time a drop of water on oxidized surface[wood] beads up.After sanding it soaks in easily.JMO yet though but have seen these scenarios many times.
I think you might be over thinking your project Aaron but do think your right in your thinking too as just like getting a good paint job so it is with sinewing and using hide glue for glueing other surfaces too.It all starts in preperation of the surface first.The base!!
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I haven't had a problem with this either, but I always like hearing other people's thoughts and opinions to help get a better understanding.
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Oh Ok...Sorry about the long winded solilquy response.I hav'nt had any problems of that either.
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Tim,
interesting info at frets about hide glue
It is never a good idea to dilute too strong a glue to obtain lower viscosity or longer working time when it is possible to use a lower grade of glue.............. high gram strength glues require up to twice the water to reach workable consistency, there will be less glue actually in the joint after it is clamped and the water evaporates.
Have you noticed any bowing due to shrinkage on your glue belly experiment?
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Aaron:
Any bad effect of oxidation is fairly insignificant, and then only on lignin. The chief danger when sinewing not-recently-surfaced wood is oil, especially from city air, deposited on the surface. Still, even in Bay Area air, I've never had a sinew to wood bonding problem, even on somewhat aged lumber surfaces. Still, if it's a concern, a very light scraping, or sanding as BowEd notes, fully eliminates any problem.
willie:
" Have you noticed any bowing due to shrinkage on your glue belly experiment? '
Sinew shrinks sideways and well as lengthwise. No problem on narrow thick limbs, but on wide thin limbs sinew shrinking sideways can concave the back, sometimes even cracking the belly. I've never had that happen but it's been reported.
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" Have you noticed any bowing due to shrinkage on your glue belly experiment? '
Sinew shrinks sideways and well as lengthwise. No problem on narrow thick limbs, but on wide thin limbs sinew shrinking sideways can concave the back, sometimes even cracking the belly. I've never had that happen but it's been reported.
Tim, let me ask a different way, seeing how you have experiments going with both sinew backs and glue bellies, can you comment about any shrinkage going on with the glue belly ones? Shrinkage that might put the bow into deflex as the glue dries?
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willie:
The pictured thin amount of dried glue belly pulled the wood into about the same amount of deflex that a same-thickness of sinew and glue wood. It's a touch less than 1/32" so just an inch of deflex. I'm expecting a 1/8" thickness to yield considerable deflex, on it's own, without being forced into position when applying the glue.
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I had no idea that hide glue had any real properties worthy of consideration. Interesting.
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And if you sinewed it first, it would be prestressing the sinew.
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dried glue (on the) belly pulled the wood into about the same amount of deflex that a same-thickness of sinew and glue wood.
hmm, so now I have to wonder if it is the glue or the sinew that does most of the shrinking when applied to a back. I would like to think it is the sinew, or other wise if glue shrinks more than sinew, then sinew in matrix might be getting compressed rather than pretensioned when drying occurs.
The admonition to not dilute the glue too much may because excess water causes more shrinkage. Could the lighter glues that need less water to have a workable consistency actually be better for this application?
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Badger:
" I had no idea that hide glue had any real properties worthy of consideration. Interesting."
Me too till recently. Google doesn't point to any non glue-like uses over time. Hard to believe. When you hold chunks or strips, or mixtures with wood or other natural fiber in hand, uses leap to mind.
The 54" redwood bow holding the pictured dried glue belly weighed 5.5oz bare. Should have been more precise because the glue belly raised its weight by less than half an ounce. Eager to see what it will do once sinewed.
willie:
A 7" sample of hide glue just dried to 6", another 51/4" sample dried to 4 3/8" That's a lot of shrinkage. And at up to 10,000-plus psi tensile strength it's going to do serious pulling, as in pulling chips free from glass as it dries. Jeff Schmidt, of the Korean Archery chapter in TBB-3, was startled one evening by an explosion in the next room; he'd left wet hide glue in a glass container that morning. Lots of hide glue glass chipping how-to on ebay.
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I mean YouTube: https://www.youtube.com/watch?v=sOVDtOok-c8
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Interesting....Do you think lower density type woods will reflex more than higher density?Just a thought.I'm sure more experiments are needed for that.Maybe more elastic type wood is more suseptible to it also.
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A 7" sample of hide glue just dried to 6", another 51/4" sample dried to 4 3/8"
Tim, can you tell a bit more about these samples? was it just a strip of glue laid down with a brush on waxed paper or cloth or something?
Interesting....I'm sure more experiments are needed....
I agree Ed. this past fall I recovered quite a bit of moose sinew and think I need to run some glue tests before I put it to use. I also bought some hide glue in three different weights 135 ,251 and 379. the mixing instruction for these three different weights call for 3:1 water ratio for the highest weight glue, and only 1.3 :1 ratio for the lightest
I have some fresh deer sinew on hand and some sample boards cut and intend to make a few tests and set them to drying this weekend.
At present I want to .....
1. mix each weight glue to the same consistency and compare shrinkage
2 . take some fresh (frozen) deer sinew and see just how much it shrinks on it's own as it dries.
I welcome any ideas from you guys for more experiments to undertake.
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With a 3:1 and a 1.3:1 I guess that means the lighter glue will "cure" quicker but maybe shrink less.
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BowEd:
"
" Do you think lower density type woods will reflex more than higher density?"
Yes, since for the most part, lower density wood is easier to bend.
willie:
"... can you tell a bit more about these samples? was it just a strip of glue laid down with a brush on waxed paper or cloth or something?
Strips of the cheapest 99-cent-store toilet paper was used, almost all air, were saturated with glue, allowed to gel hard then hung up to dry. A few hours later it's hard springy, dry, and shrunk.
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Strips of the cheapest 99-cent-store toilet paper was used, almost all air, were saturated with glue, allowed to gel hard then hung up to dry. A few hours later it's hard springy, dry, and shrunk.
as good a medium as any. will test my glue the same, tx
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It's my point exactly.The lighter density wood I've worked with has been compression strong/tension weak.Example red cedar.Don't know about others like redwood though.I have some redwood from building a green house with it.Very light weight stuff but does'nt rot any.
Seems the wood would need to be sinew backed too.Which was probably your intentions too.
There are lightweight whitewoods like hackberry that is tension strong or compression weak like hickory that would benefit from the glue belly maybe,but it seems most times it does real well just sinew backed alone.Both doing well with just a heat treated belly and no sinew at all.
I might not be fully envisioning your intentions though.
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What test samples look like if hung up to dry wet. These used paper towel strips.
The top sample is a single layer saturated with glue. The bottom sample is three layers, saturated then put together. They didn't begin deforming till past the hard gel stage. To get flat dried samples, once at the hard gel stage, no longer wet to the touch, set them on several layers of PT, then several layers on top, then a not-too-heavy book. Replace the wet papers every couple of hours, then every day, till hard dry.
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BowEd:
" Seems the wood would need to be sinew backed too.Which was probably your intentions too."
Your posting hit a few seconds before mine...
Yes, it will pulled into a bit more reflex then sinewed, on a fairly high crown.
The reflex taken with that thin glue layer, would have been a bit more but the handle is stiff.
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Are you of the belief that this bow will not chrysal readily?
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One would think that sinew would protect a wood low on elasticity from chrysalling but it doesn't. A sinew backed highly reflexed Black Cherry recurve I made many years ago chrysalled badly well before I got to full draw
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It seems to me that even though sinew and glue is theoretically very stretchy is still acts like a steel strap when placed over weak wood.
I had an Elm bow that I sinewed and it chrysaled like pine just getting it back to a straight profile which didn't make much sense at all. I pulled it back to 32 inches anyway and it still had remarkable cast for being a mushy mess.
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PatM:
" Are you of the belief that this bow will not chrysal readily?"
Hard to know. I can't find figures on the compression strength or elasticity of dried hide glue. This is a fist test. But judging by its elasticity and strength in tension it seems realistic to think the glue belly will hold up.
Marc:
" A sinew backed highly reflexed Black Cherry recurve I made many years ago chrysalled badly well before I got to full draw"
If your cherry recurve had had a horn belly it would'nt have chrysaled; the idea here is to see to what extent this poor-man's version of horn will function like horn. Lots of possibilities if it even comes close. Several tests needed to know one way or the other.
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I believe very much that the hide glue will deform or crack under the compression forces. However, using a matrix of glue with a fibre in it should hold it better. I am orderung some horse hair next week to do a parallel test with you on this to see if a difference in performance is to be had. Id like my horse hair belly to be as thick as your glue only belly.
I am curious, what the specific gravity of hide glue vs different horns, and antler is.
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One would think that sinew would protect a wood low on elasticity from chrysalling but it doesn't. A sinew backed highly reflexed Black Cherry recurve I made many years ago chrysalled badly well before I got to full draw
It seems to me that even though sinew and glue is theoretically very stretchy is still acts like a steel strap when placed over weak wood.
I had an Elm bow that I sinewed and it chrysaled like pine just getting it back to a straight profile which didn't make much sense at all. I pulled it back to 32 inches anyway and it still had remarkable cast for being a mushy mess.
I dunno about these generalizations about sinew. How much sinew compared to the quality of the elm or cherry has to be considered
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Now i wonder about repairing chrysles by putting hide glue in them. The weak spot would be beefed up by the glue filling the cracks.
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One would think that sinew would protect a wood low on elasticity from chrysalling but it doesn't. A sinew backed highly reflexed Black Cherry recurve I made many years ago chrysalled badly well before I got to full draw
It seems to me that even though sinew and glue is theoretically very stretchy is still acts like a steel strap when placed over weak wood.
I had an Elm bow that I sinewed and it chrysaled like pine just getting it back to a straight profile which didn't make much sense at all. I pulled it back to 32 inches anyway and it still had remarkable cast for being a mushy mess.
I dunno about these generalizations about sinew. How much sinew compared to the quality of the elm or cherry has to be considered
Those are just observations. The quantity of sinew was a typical amount. The quality of the wood is hard to really judge until you actually turn it into the bow.
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No, it's not the blob from outer space. It's what happens when you make a 1/2" thick pouring of hide glue and wait for it to dry down to a hard sheet. Might add antibiotics to the next try.
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Thats funny, cause isnt hide glue what they use for petri dishes?
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isn't that agar? jello for vegans?
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Just did a backward sinew shrink test: Measured the sinew stiff and dry, then let it soak in warm water for an hour and measured again. The original 12" became about 12.5 inches, in the range of 3% to 4% commonly reported.
This is dramatically different than the roughly 15% to 20% the earlier-pictured hide glue tests showed.
So when we sinew back a bow the glue is trying to shrink roughly 4 time more than the sinew, therefor working to pull the sinew shorter than the sinew's normal 4% would like to. On top of that the glue itself is able to stretch up to 10%.... So some way complicated mechanical interactions are at play when a sinewed bow is drawn. Understanding them will surely lead to better bows, but doing so is going to take several gallons of midnight oil.
So, does it hurt or help to use a higher or lower % of glue?
Quite a bit earlier in this thread someone suggested that sinew mixed with glue might have quite different properties than sinew alone. Who was that, so he can get a 50 point bonus?
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12"
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Excessive hide glue on a bows back tends to crackle when drawn. I doubt it will be beneficial to add more hide glue than needed to bond sinew on the back.
On a belly, i can see it helping. I had an image flash in my mind of cut grooves in a belly as if grooving to lay horn in, filled with glue. That would be an interesting way to possibly keep the glue from deforming under compression strain.
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Might add antibiotics to the next try.
I read they say to add vinegar to hide glue to preserve from mold and microorganism
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sleek:
" Excessive hide glue on a bows back tends to crackle when drawn. I doubt it will be beneficial to add more hide glue than needed to bond sinew on the back"
The question was targeting the ideal % of glue in the glue/sinew mix itself, given the difference % of shrinkage for glue and sinew: Yes, when resting above the sinew surface, glue will sometimes crack when highly stressed. But high-quality glue can stretch 10%, so cracking glue on a wood bow is likely just the bow giving its opinion of the glue's quality.
Your idea of glue-filled grooves in the belly surface is worth experiment with. The interface would have the average or both materials. More tests....
I wonder if there's any way to cause hide glue to run up the pores of ring-porous wood. Hot wood would keep it liquid, capillary action should work to some extent, slight suction on the other end might bring the glue all the way through. Seems a challenge, but a glue/wood hybrid belly has possibilities.
GlisGlis:
" I read they say to add vinegar to hide glue to preserve from mold and microorganism"
Thanks. I'll read up on that.
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I suggested that sinew and glue together might be different synergistically.
We did have a discussion on here before where the composite guys were pushing for higher amounts of glue as THE only way while others thought experimenting with lowering content and getting optimum infusion through the fibers might be better.
That was back before feisty mikey had another tantrum and quit the board again. ;)
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If using hide glue improves the sinew backing, then isn't that a plus over using titebond?
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Absolutely Bob.The combo is as they say mother natures FG.The only 2 reasons to use titebond is for convenience and most times worries about humidity and moisture protection.Performance is stunted dramatically.
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I also had a sinew backed Elm chrysal badly, it was a reflex deflex. The bow shot quite well but lost cast swiftly.
One would think that sinew would protect a wood low on elasticity from chrysalling but it doesn't. A sinew backed highly reflexed Black Cherry recurve I made many years ago chrysalled badly well before I got to full draw
It seems to me that even though sinew and glue is theoretically very stretchy is still acts like a steel strap when placed over weak wood.
I had an Elm bow that I sinewed and it chrysaled like pine just getting it back to a straight profile which didn't make much sense at all. I pulled it back to 32 inches anyway and it still had remarkable cast for being a mushy mess.
I dunno about these generalizations about sinew. How much sinew compared to the quality of the elm or cherry has to be considered
I always mounded my sinew regardless of bow design so that most of it was down the middle of the limb. This should have taken some stress off the belly.
Marc:
" A sinew backed highly reflexed Black Cherry recurve I made many years ago chrysalled badly well before I got to full draw"
If your cherry recurve had had a horn belly it would'nt have chrysaled; the idea here is to see to what extent this poor-man's version of horn will function like horn. Lots of possibilities if it even comes close. Several tests needed to know one way or the other.
Of course but that was not what I was making. I ended up removing most of the Cherry and gluing down a strip of Osage essentially making the bow a complex composite. Still have that bow and it shoots quite well.
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That's what I've got to do to my cherry sinewed black cherry I liked.I'm just beginning to see a few chrysals.It started to chrysal after around 2000 shots or so.Just with only 4" of reflex.
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So when we sinew back a bow the glue is trying to shrink roughly 4 time more than the sinew, therefor working to pull the sinew shorter than the sinew's normal 4% would like to. On top of that the glue itself is able to stretch up to 10%.... So some way complicated mechanical interactions are at play when a sinewed bow is drawn. Understanding them will surely lead to better bows, but doing so is going to take several gallons of midnight oil.
So, does it hurt or help to use a higher or lower % of glue?
Tim, I have some glue on TP strips drying now? How long did it take for yours to shrink the 15-20% ? Three different grades mixed with the recommended amount of water. I am glad you did the reconstituted sinew test, I have some fresh sinew drying at the moment also. How long before you measured your sinew?
Do you think it is the % of glue to sinew in the matrix that matters about shrinkage? I am going to try to wet out a TP strip with glue thinned with excess water.
If one dries a strand of sinew like a guitar string, it gets shorter and tighter, or becomes post tensioned. Is that the effect we want to duplicate on a bow back? Seems like if glue tends to shrink excessively, we might be better off to restrain the bow from reflexing as it dries, rather than encouraging it?
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I always mounded my sinew regardless of bow design so that most of it was down the middle of the limb. This should have taken some stress off the belly.
guess I should have said how much and how thick also. the" taking the strain off the belly" idea has a lot to do with proportions, there is always the "too much of a good thing" possibility
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Absolutely Bob.The combo is as they say mother natures FG.The only 2 reasons to use titebond is for convenience and most times worries about humidity and moisture protection.Performance is stunted dramatically.
Ed, when you tried it with titebond did you encourage the bow to go int reflex by reverse stringing?
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I always mounded my sinew regardless of bow design so that most of it was down the middle of the limb. This should have taken some stress off the belly.
guess I should have said how much and how thick also. the" taking the strain off the belly" idea has a lot to do with proportions, there is always the "too much of a good thing" possibility
And proportion has a lot to do with how much of it is working
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PatM
" I suggested that sinew and glue together might be different synergistically."
I should have paid more attention. The 50 points is yours. You're tied with BowEd
This is a fascinating puzzle... given that they're mixed together, and given their great difference in behaviors, the ratio of glue to sinew is bound to make a large difference in performance. And it likely can't be calculated, a series of ratio tests needed.
Willie:
" Tim, I have some glue on TP strips drying now? How long did it take for yours to shrink the 15-20% ?"
If single strips, and hung in air to dry, just a few hours. But if not allowed to hard gel first, then put under mild pressure between multiple layers of paper towels or such, the towels changed periodically, the sample will become deformed and corrugated. It can take a two or three day the towel/pressure way.
Haven't tried this with different glue grades and dilutions.
Here's piece of the earlier-mentioned hide-glue foam. About .5 or .10 specific gravity but so touch a thumb nail won't dent it, even given the pressure that dents oak.
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Willie....I've never used titebond with sinew,but have seen it done.The benefits and resiliency are not there without using hide glue in the tension department.Maybe they are in the compression department.I would'nt know that nor have I seen it used.
In other words when using titebond with the sinew it serves more as bullet proof backing with the extra mass weight of the sinew not working for it's fair share of the working load.I'm not sure it would do much better in compression either carrying it's fair share of work compared to it's mass weight.
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Enjoyed the civil and productive exchanges. Thanks all. I'm leaving this site for less restrictive pastures. I'll be posting on the PaleoPlanet site.
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From the dealings I have had with you in the past Tim I have come to realize that it is either your way or the highway. Your inability to have respect for the people who bring this site to the good people here indicates that you are not suited to being here.
Good luck and good bye.
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From the dealings I have had with you in the past Tim I have come to realize that it is either your way or the highway. Your inability to have respect for the people who bring this site to the good people here indicates that you are not suited to being here.
Good luck and good bye.
Marc, a person who speaks their mind clearly is rare and respectable, but perhaps that message could have been a private one?
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It started out private and Tim brought it on here looking for support.
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It started out private and Tim brought it on here looking for support.
Well i guess i have no clue wtf is going on. Sorry.
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Read the thread below and it will be clear.
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Funny stuff between the two threads, I needed a chuckle. I don't know Tim and probably haven't read two paragraphs of his writings, so no opinion on his presence here or gone. What I do know is PA and wood bow builders will continue on better than ever no matter who frequents the proverbial PA bar stools.
P.S. Good rules don't have grey areas. And the link rule isn't grey.
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Read the thread below and it will be clear.
I see. Terrible situation to have happen.
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One easy method for directing attention to pages outside PA has been accomplished with the # "insert code" button in the editor. It's my understanding an url can be posted, just not as a clickable hyperlink
http://www.primitivearcher.com/smf/index.php/topic,63321.0.htmlone extra step to post, one extra step to read the linked page
Just click on "select", then copy and paste into new address bar
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As Pat said, I started it out as a PM to Tim, that wasn't good enough for him and he brought it out on the board.
It's easy enough to disable a link and still get your message across, don't know why he though that was unacceptable.
Glad you had a chuckle Chris.
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I meant that with all due respect. I thought it was funny how childish someone could be over something so petty and insignificant in the picture of life. Passion is one thing. Arrogance or ignorance, which rhymes :), are another.
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I've never met Tim myself but My friend Gary did at the first Mo Jam.Many things he's written are spot on.In fact most,but with the good comes some bad too.
I'm with the rest can't understanding why someone would think he's above any authority.
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I was a Moderator on Paleoplanet when he pitched his little temper tantrum and said he was leaving. Well the rule got changed for Tim and they created a new category to make him feel better and not leave. So, I left.
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He said he was outta here on the 28th and showed back up on the 29th to snoop around. Must have missed you, Eddie.
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Ol' Ken told us a different story for his departure over there. ;)
I still remember Tim's PA article where he threw a glass backing on a hickory board bow and that was all justifiable. His own personal rules were rather fluid.
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Well, regardless of all the drama, there is still a lot of good in this thread. Can we keep going with the effort of learning?
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He said he was outta here on the 28th and showed back up on the 29th to snoop around. Must have missed you, Eddie.
Must have been a shock for him to find out he was banned
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I thought I would clarify the above statement of his being banned, just in case.
Tim does have interesting ideas so if he changes his attitude and starts to respect this forum and the rules then I will suggest that we lift the ban.
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BowEd:
Yes, it's whale baleen. You win the 50 points, duly recorded. They're fully transferable and can be traded with other point holders or used to make purchases in the paleo economy,btc margin (https://www.delta.exchange/futures-guide-bitcoin/). Just kidding, but not a bad idea.
sleek:
" I have seen baleen used as backing, but does it work as a belly?
Yes. As belly material it stand about half way between horn and bow wood itself. The Asiatic-style bow on page 87 of TBB-1 used baleen on the belly.
PatM:
The glue belly in the photo on the previous page was brushed on. Maybe ten coats. Three layers of TP/glue yields the same thickness, and much more uniformly. It's best to use cheap, thin, almost see-through versions, and to peel its two layers apart, each layer more air than fiber.
Sleek:
Knox Gelatin, and similar, is surprisingly high-quality glue, with a bloom or gel strength of about 300, just about the highest of any glue.
great post thanks