Primitive Archer
Main Discussion Area => Bows => Topic started by: DC on February 24, 2017, 01:04:24 pm
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This has bugged me for a long time and I haven't been able to sort it out on my own. Why/how does sinew help a bow bend so much? I've read that sinew stretches something like six times as much as wood. If that's the case why doesn't the wood just break under the sinew? If the sinew stretches that much why is it any more effective than gluing a piece of rubber to the back?
How does putting sinew on the back protect the belly?
If someone has a link to a good explanation that would be great too.
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I just had a very similar conversation to your question it boils down to the outer 10% of the limbs depth does 90% of the work ,the sinew being able to stretch 10% more then wood & the wood beneath is being relieved of part of the tension load , allowing for a highly stressed limb to function better then wood alone , thats my shot at the answer if that worked for you !
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Sinew in a glue matrix likely doesn't stretch THAT much but wood can break under sinew. As far as sinew protecting the belly...probably not as much as the old speculations would have us believe.
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Yes sinew can stretch a lot further than the 1% wood can be stretched. It has much lower resistance to stretching than wood and is around 1.3 s.g.
It protects the wood underneath if there is sufficient thickness to stop the wood feeling much tension. If you don't use enough sinew then the wood will break if pulled far enough. Sinew never gets to the point where it will break on a wooden bow and even a hornbow won't fail because the sinew failed. It is incredible stuff.
Sinew doesn't 'protect' the belly. If anything a sinewed wood bow should 'short' for its drawlength and therefore the belly is going to be bent to a greater degree than if the bow was wood only. That's why it is really only worth sinewing the better more elastic woods.
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I wonder if the sinew starts to stretch with a bit less pressure than the natural wood back wood. Making the back stretch a bit more earlier in the flex of the limbs. So that the wood belly is under less strain for the same amount of flex it's under. Allowing even low compression strong woods to bend a bit more before giving in.
Kyle
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The outer most surface of the bow is doing the most work and the deeper you go into the limb the lower the strain. With enough sinew the wood won't be feeling tension.
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If that's the case why doesn't the wood just break under the sinew?
because the wood is much thinner than a comparable bow without the sinew
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I just had a very similar conversation to your question it boils down to the outer 10% of the limbs depth does 90% of the work ,the sinew being able to stretch 10% more then wood & the wood beneath is being relieved of part of the tension load , allowing for a highly stressed limb to function better then wood alone , thats my shot at the answer if that worked for you !
+1 to that.
Something else that hasn't been mentioned, sinew along with any other backing will keep the wood from splintering up on the back. Most times when a self-bow breaks its not because the back was over its tension capabilities, it was because of the geometry of the bend that allows any imperfection to lift off catalyzing disaster. This is way even weak thin backings like paper can still be so effective.
Sinew won't help the belly at all. The only way it could is if you make your bow thinner to compensate for extra poundage you didn't want at the same draw. In most cases it stresses the belly more either because you can bend the bow further than most self bows, of you use more material with the same bend relying on the sinew to keep the back from breaking from the greater stress. The belly benefits nothing from the sinew under that greater stress. This is why i started the discussion on compression woods, so i would know what would be best for those highly stressed designs.
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if the wood was wider and thinner because the sinew on the back,, wouldnt that be reducing the strain on the belly???
I know after a point when the draw is extended ,, your gonna need horn,, but at a reasonalbe draw,, I am just wondering,, I have had wood backings crush a belly,, but I have never had sinew back crush the belly on a bow drawn to half the length of the bow,,
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Yes Brad.Good point.Sinew will stretch so much farther than a wood backing which is'nt as hard on the belly then.
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But wide and thin doesn't stretch the sinew as much. Sinew backed Native bows come in the two extremes, wide and thin or narrow and deep. Which shoots farther?
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a wide thin yew would shoot further????
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I know that sinew loves to torque reflex on wide thin limbs if applied thick enough and will stretch it plenty.Even with shrinking a certain percentage sideways too.I think there's too many factors to answer a question like that right off hand.Design and length wise are not known.That factors into it too.
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This is some thing I have always wondered if you have a sinew bow that's reflexed say 4 in. & when you bring it to brace is the belly under more compretion then a standard brace at that point ? This is a great thread.
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I have never done a sinew backed bow other than my HHB mini bow for Marshall. I am thinking of doing a HHB and reading this post wondering thoughts on if HHB is a good candidate and what type of design? For myself I'd probably shoot for around 60 lbs at 25" draw. Hope this isn't getting to far off topic.
Bjrogg
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if you have a sinew bow that's reflexed say 4 in. & when you bring it to brace is the belly under more compretion then a standard brace at that point ?
the belly of the sinewed reflexed bow would be under less compression than an unsinewed reflexed bow, because with all other things being equal, the sinew will stretch before most woods will compress.
if you are comparing a reflexed sinewed bow to a unreflexed self (no sinew) bow, than the degree of compression would depend on the amount and strength of the sinew and the relative strength of the wood it is applied to.
I think Mo cooncatcher describes the properties of sinew well, as sinew is often used to its best advantage with low compression strong wood. Work or energy stored in the limb is a result of materiel actually moving (and returning to shape).
My anwser to Pats riddle is, One can build a bow from sinew and something very stiff, but essentially, it would be a sinew bow. As the sinew would be doing most of the work, the overly stiff belly would not contribute much to the energy storage. I think that the wide thin yew would shoot further, but I might be proven wrong.
I have to disagree a bit with.....
Sinew won't help the belly at all. The only way it could is if you make your bow thinner
as I believe that the application of a backing like sinew does makes the compression side of the bow thinner, by lowering the level in the core that neither stretching nor compression takes place. Correspondingly, the tension side increases in thickness, and the overall thickness does not change all that much.
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Hmmmmm :)
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The farthest shooter is.....The one that is the most efficient with the longest power stroke with the poundage being the same of all bows.
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if the wood was wider and thinner because the sinew on the back,, wouldnt that be reducing the strain on the belly???
I know after a point when the draw is extended ,, your gonna need horn,, but at a reasonalbe draw,, I am just wondering,, I have had wood backings crush a belly,, but I have never had sinew back crush the belly on a bow drawn to half the length of the bow,,
I don't see how sinew would make a bow wider and thiner? whether the bow is wide or thin is purely based off your design. But yes a wider bow will have less compression than a thinner thicker bow, even if both have the same mass of wood. What you have to understand is the only factors that affect the total tension or compression stress the specific fibers undergo, is their distance from the core line from a side profile or how far they bend. If two bows were the same thickness but one had a much stiffer material on the back, like sinew, there still wouldn't be any difference from the compression forces on the belly. The latter bow would have a higher poundage, due simply to the stiffer sinew, not that there was more compression on the belly.
I realize that I overemphasized that sinew doesn't help the belly out. I only emphasized that because I assumed that the reason to use sinew was for a more stressful design (either further bend/draw for length, or higher poundage). If you are going for a less stressed design with the same poundage and draw, sinew should help with compression. This is only because you could take more wood off (thus thinning the depth) to get the same poundage since sinew is stiffer than wood.
This is some thing I have always wondered if you have a sinew bow that's reflexed say 4 in. & when you bring it to brace is the belly under more compression then a standard brace at that point? This is a great thread.
Yes, it would be. the stress on a fiber is based on the distance bent and thickness. The thicker the wood the more stressed the fibers. The farther they have to bend the more stressed they become. Since it is reflexed the limbs have to bend farther to get to brace, therefore the fibers on both the back and belly are under greater stress than a bow that didn't have to bend that far to brace.
After researching it, and giving long thought about the deflex-reflex design, the more I'm leaning away from reflexing the limbs. I'm starting to think its just stressing the limbs unnecessarily, because as soon as you brace a bow it essentially zeros out the poundage.
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If I understand this correctly. Because the sinew is put on bow with reflex added and sinew dried adding even more reflex. The unbraced bows belly is actually slightly stretched or under slight tension. When braced it goes past neutral to compressed but less so because sinew is doing most of the work. Playing devils advocate wouldn't there need to be a equal opposite force?
Bjrogg
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Sinew in a glue matrix likely doesn't stretch THAT much but wood can break under sinew. As far as sinew protecting the belly...probably not as much as the old speculations would have us believe.
Hi Pat,
I agree with you, and so I'd like to ask.... Wouldn't a sinew CABLE be better than a simple glued-on sinew backing? The sinew cable can be twisted to enormous tension -- and what stretches better than a cable? You can adjust it when it loosens up in humidity. No drying time necessary. Can be quickly removed if bow breaks. Why not sinew cables??? It just seems like the better idea.
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I dont think reflexing is stressing unnecessarily ,, it can add cast to the bow,, a chrono will varify that on two like bows,,
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cables are out of my area of expertise,, I am assuming if they were better,, we would have seen more of them in use,, just guessing here,,
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I'm thinking like BJ the reflex bow is in negitive compretion due to the reflex and at nutrel you have a bow that is not under compretion but will have a earlier draw weight then a standard bow giving you a longer power stroke threw out the release if I'm thinking right.
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cables are out of my area of expertise,, I am assuming if they were better,, we would have seen more of them in use,, just guessing here,,
Maybe. But that's like going back in time to the flintlock days and saying "if repeating guns are better, we'd see more in use". After all, they existed in the 1700s. (https://en.wikipedia.org/wiki/Girandoni_air_rifle) Could it be that the Inuit were simply more evolved? Climactic extremes and fewer quality resources can kickstart technological and evolutionary progress. Most people were too stupid to figure out how to make a cable bow, and always stuck with the "any idiot can do it" method of gluing sinew on a bow, because they were never pushed by necessity to come up with a new (and potentially better) way. The best idea is never the most widespread idea, in the beginning.
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I suppose that it makes a difference if the reflex is natural, or was induced by bending into reflex prior to the application of the sinew and/or created by the shrinking of sinew as it dries.
built a cable bow once, 41" long, pulled it to 80# @ 21". the limbs did not spring back when I took the string off
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The ironic thing is that, in their natural state, our tendons function as cables and most closely resemble them. The same thing can be said for human muscles. A human muscle with tendons is like a cable with two main attachment points, they're not glued over our bones in layers. Imagine how poorly our bodies would function, if our mechanical parts were glued. Our brittle and unflexible bones would be much more prone to snappage, if they weren't cable backed.
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If I understand this correctly. Because the sinew is put on bow with reflex added and sinew dried adding even more reflex. The unbraced bows belly is actually slightly stretched or under slight tension. When braced it goes past neutral to compressed but less so because sinew is doing most of the work. Playing devils advocate wouldn't there need to be a equal opposite force?
Bjrogg
Like mentioned it depends on how the reflex is brought about. If it's steamed or heat-treated then the belly would be under more compression. If it's stretched there as in perry reflex or from dried sinew it will be under less compression. It all depends on the natural plane of the fibers. There must be something I'm not understanding with reflex. Wood acts much like a natural spring. Meaning that the restorative force is proportional to its stiffness (spring constant/elastic modulus) and deflection. Just as Tim Baker said, a bow doesn't gain stiffness when it is bent further. Stacking is due to string angle. If anything the wood gets less stiff as it is bent further once it passes the yield point. So reflexing the limbs (with steam) shouldn't change the stiffness of the material at all in later draw. What must be going on is there is a lag before a material gets to its true stiffness, so a little bit of reflex may be good. I just can't see how something greater than 3-4 inches would do anygood.
cables are out of my area of expertise,, I am assuming if they were better,, we would have seen more of them in use,, just guessing here,,
Maybe. But that's like going back in time to the flintlock days and saying "if repeating guns are better, we'd see more in use". After all, they existed in the 1700s. (https://en.wikipedia.org/wiki/Girandoni_air_rifle) Could it be that the Inuit were simply more evolved? Climactic extremes and fewer quality resources can kickstart technological and evolutionary progress. Most people were too stupid to figure out how to make a cable bow, and always stuck with the "any idiot can do it" method of gluing sinew on a bow, because they were never pushed by necessity to come up with a new (and potentially better) way. The best idea is never the most widespread idea, in the beginning.
+1 to that. I think we shouldn't be afraid to challenge current thought. Just because that's how its normally perceived doesn't mean its correct. It most likely, but it still isn't infallible.
As far as cables are concerned, I think they are great. I've sinewed two bows, and paper backed two others. Of the four, two of them also were cable backed. The cable really does help. The problem with doing cable over gluing is that you don't get the added benefit of keeping the fibers down. But other than that i think it is superior to gluing in regards to adding weight due to tension stiffness. The reason we don't see it more I think is twofold. 1) it's hard to make it look good, and 2) it's harder still to secure it to the bow and keeping it close to the back.
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From all the Chrono info on cable backed bows that I have seen they don't seem to be any where close to the speed gained buy reflexed sinew bows , I'm with Brad I think you would see a lot more of them if they where efficient , they are neat looking bows that you see in some of the native indian books thoe.
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gfugal, you believe sinew backing is a stiff material?
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I've sinewed two bows, and paper backed two others. Of the four, two of them also were cable backed
Greg, did you have more set than expected on the cable bows?, or were the limbs thinner than would be, without the cable?
Just curious how massive the sinew cable was. Pics?
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gfugal, you believe sinew backing is a stiff material?
I thought irlt was, but you made me question it so i reviewed the data JoachimM gave me and it turns out it has a modulus of elasticity around 7. Thats stiffer than some woods but not usual bow woods. So i'll have to revise my stance. Sinew usually isn't more stiff than wood. It is however very flexible meaning it can stretch much further than wood can. I would say then that the benefits of sinew backing are probably due to it keeping fibers down, reflexing a limb, and its ability to flex without breaking. I'm going to have to change my posistion and say sinew probably wouldn't make the best cable. Flax, Jute, and Hemp however have 3 times or more the stiffness so they would make a better cable.
I've sinewed two bows, and paper backed two others. Of the four, two of them also were cable backed
Greg, did you have more set than expected on the cable bows?, or were the limbs thinner than would be, without the cable?
Just curious how massive the sinew cable was. Pics?
Yes my cable bows had horrible set. Not because of the cable but because i was drawing 43 inch bows with non working handles 27 inches. The compression damage was do to how far i bent them, not because they had a stiff material on the back. I also didn't use sinew for the cables. I used pollyester thread twisted into something like a bow string.
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This has bugged me for a long time and I haven't been able to sort it out on my own. Why/how does sinew help a bow bend so much? I've read that sinew stretches something like six times as much as wood. If that's the case why doesn't the wood just break under the sinew?
To get back to the original question: Sinew CAN stretch 6 times as much, but that doesn't mean it does it on every bow and throughout the depth of the sinew layer.
Sinewed wood bows will stretch at the back maybe 2%, in extreme cases 2.5%.
If you would make sinew at the surface of a bow with a wooden belly stretch 5%, the belly would effectively fret and collapse.
Sinew will stretch to about 5% on Turkish sinew-wood-horn composites, but only at its surface. The first layer, which is glued to the wooden core, will be stretched less than 1% (as the wood core needs to be kept intact as well, it cannot stretch more than 1% at the most or it will break).
The reason sinew is so interesting has to do with the shift of the neutral plane that backings give to a bow.
Since wood is a bit stronger in tension than in compression, the neutral plane of a self bow is about 33% from the back of the bow: 1/3 of the wood works in tension, 2/3 work in compression.
The opposite backing of sinew is flax: it cannot stretch very far, and needs a lot of force to stretch a tiny bit. If you add a 1.5 mm layer of flax backing to a 30 pound bow, you'll get a 60 pound bow (but short-lived): Because the flax is so strong, all the tension is carried by the flax, and the neutral plane will shift to just under the flax. The entire wood thickness (nearly double of before) now needs to work in compression, with dramatic results: if you're lucky, it just frets all over the place and takes set, if you're not, it buckles at some point and leads to an explosive break of wood (and flax) (been there). Paper thin backings of flax can be interesting to protect a back with grain violations from breaking.
Since sinew is both very elastic (it can stretch far) and has a low modulus of elasticity (it starts to stretch under low forces already), you need a decent layer to make it really work. Add a dense wood to it as a belly, such as osage (with the extra plus that osage is superb in compression), and you have a belly that doesn't need to work extra hard. Add 3 mm of sinew to a 30 pound bow, and you'll get 45 pound bow or so, but the neutral plane will shift just a tiny bit towards the back, and for a now stronger bow, there's just a minute amount of extra belly depth needed (or the belly surface is compressed just a little bit more).
(Do consider the numbers given here as thought experiments, not as facts)
Moreover, sinew has the extra advantage of shrinking when drying, so it pre-loads the bow by pulling the belly into tension and the back into compression! When you brace the bow, you first need to overcome this extra force, and you get a higher string tension at brace. The belly isn't put under more strain because of this, its kind of a free ride offered by the reflexed sinew.
There's an extra advantage in dry conditions. Tension strength of wood peaks at 12% MC, and decreases at lower and higher MC. Compression strength of wood only gets higher at lower MC. That's why very dry selfbows break when MC drops too much: tillered for higher MC, the neutral plane shifts towards the belly at low MC, and the backs are overstrained when drawn.
Tension strength of sinew also gets higher at lower MC. So in dry climates, sinew and wood complement each other extremely well, as they keep pace. The same goes for horn, by the way. That's why horn bows are kept as dry as possible.
So to summarize, sinew doesn't protect the belly, but it doesn't require a lot of extra strain either from the belly relative to the extra draw weight it adds. And in dry climates, it effectively protects the back from breaking.
that's my 2ct
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perhaps someone can help me understand what is happening with some fiber back samples I tested earlier this winter.
I made up about a half a dozen test samples, and bent them in a bend test, noting the MOE, MOR , and % strain at where set became noticeable.
Although I would not post a synthetic backed bow on this Primitive only forum, I mention this test, because it may be appropriate in a discussion of different backing applications. The fiber was vectran which is known to be very stiff, and have very low creep. specs on the fiber show it to be capable of elongation of 4%, similar to flax and approx 4 times that of which wood is considered to be able to stretch on a bows back.
Missing in a lot of discussions of backings that stretch, is the need to use the appropriate amount of fiber to put the stretching in a range of usefulness. If you hang a weight of x lbs from a string, and it stretches y inches, then halving or doubling the weight should half or double the stretch. Same with a backing in a matrix I assume.
With something like sinew, a shallow layer will stretch ok, but might separate from the back it is glued to, when the wood immediately underneath fails.Typically because the wood is not able to stretch/bend near as much as needed to accommodate your sinew backed "design" bend. If sinew is placed in a very thick layer, the outer surface will stretch enough to permit bends that wood will not, but further down in the cross section where the sinew/wood glue line is, the limb materiel is not required to do near as much stretching as what happens at the outer surface of the back. So much for a backing that is less stiff than the wood it is applied to.
In the case of vectran, and I assume similar backings such as flax, I found that in small amounts, it would stretch along with the underlying wood until the wood failed, similar to the action of sinew, but I noticed no increase in the MOE/stiffness of the sample as a whole or much benefit to having the thin layer of backing. Why no improvement?
In increasingly heavier applications of backing, set taking happened sooner and MOR/ultimate strength decreased or remained the same over the unbacked (control) sample. Considering all samples, the control performed just as well as the best, and MOE/stiffness remained relatively unchanged across all tested samples. There were a few samples that had moderate amounts of backing, where the backing could be said to protect the back from breaking, but well past the point of the belly taking the amount of set that would be desirable in a bow. Fiber applied over a knot or defect might have its place, though.
What is going on here? I thought stiff backings might offer improvements :(
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What did you glue the vectran with? To me discussing any fiber is useful for a material understanding.
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PatM
some with hide glue, others with system 3, no noticeable difference on account of adhesive, although this test was not designed to compare glues.
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You have to factor in how well the glue actually bonds with the fiber though.
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"factor in"? like how?
The values reported were at strain levels up to where set began. The only glue/ fiber failures I noticed were well beyond strains levels usable in a bow, ie. at the breaking points of the samples. In very light applications of fiber, they stretched away and separated from the wood when the wood broke slowly. In samples with moderate amounts of fiber, the fiber break was clean similar to tension break in brash wood, and of course the samples with excessive fiber just crushed the wood without breaking the fiber.
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This is what's great about this forum, you can learn so many things. It gives us new people a huge learning curve. For example, i was basing all my thought expiramemts on the idea that the neutral plane is always the exact center of limb thickness. I suppose then that differing stiffness in back and front can effect the each other. I'll have to re-examine what i said earlier.
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Greg
here is a link to a paper might be pertinent. I find interesting about the effect of knots, and it actually cites some values for MOE tension, which were obtained in an actual tension test. Most data you find about wood tension is estimated from bend tests and compression tests.
https://www.researchgate.net/profile/Rakesh_Gupta24/publication/258111089_Revisiting_the_neutral_axis_in_wood_beams/links/53d7f3c10cf2a19eee7fe792/Revisiting-the-neutral-axis-in-wood-beams.pdf
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Thanks for all the responses, it turned into a great thread. I think that what I was missing before was that it doesn't matter how much the sinew stretches.( I was hung up on the sinew stretching more than the wood) What matters is the amount of force necessary to stretch each a given distance. As long as it takes more force to stretch the sinew than it takes to stretch the wood then the wood will be protected. I still haven't quite sorted how/if it protects the belly though. It's probably something to do with the neutral zone, but until the Federation/ Romulan problems are sorted it may remain a mystery ;D ;D
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Thanks for posting the thread there MR DC one of the best ones we have had in a while learned a lot.
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In the case of vectran, and I assume similar backings such as flax, I found that in small amounts, it would stretch along with the underlying wood until the wood failed, similar to the action of sinew, but I noticed no increase in the MOE/stiffness of the sample as a whole or any benefit to having the thin layer of backing. Why?
In increasingly heavier applications of backing, set taking happened sooner and MOR/ultimate strength decreased or remained the same over the unbacked (control) sample. Considering all samples, the control performed as well as the best, and MOE/stiffness remained relatively unchanged across all tested samples.
What is going on here? :(
Willie, two thoughts:
First, maybe your test method is just not accurate enough, is too noisy to detect differences.
Any raw data we might munch through?
Second: if the wood starts to take set, it is effectively being crushed. as you continue to compress it, your bos effectively functionally a bit less thick as the belly wood beneath the belly surface is now taking the compression, the wood at the belly surface is just dead mass now, not pushing against the force anymore. So basically, the force required to make the samples bend is mostly determined by the compression qualities of the wood, less the tension strength of the backing.
With a strong fiber backing, set is expected to happen sooner (when considered as the amount the sample is bent, not the force required), as more belly depth is being asked to work in compression. When the wood (being asked to work in compression) is thicker, you reach the proportional limit at a lower bend radius.
Joachim
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Joachim, look in your email. I tried to format the data in the editor for the forum post, but not too usable, and can't seem to attach either.
If anyone wishes to review the data, please PM your email address.
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"factor in"? like how?
The values reported were at strain levels up to where set began. The only glue/ fiber failures I noticed were well beyond strains levels usable in a bow, ie. at the breaking points of the samples. In very light applications of fiber, they stretched away and separated from the wood when the wood broke slowly. In samples with moderate amounts of fiber, the fiber break was clean similar to tension break in brash wood, and of course the samples with excessive fiber just crushed the wood without breaking the fiber.
Some fibers do not bond well with the glue so when you start bending the sample the fibres move inside the matrix rather than functioning like a linked composite. That usually requires microscopic examination.
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I agree with Joachim. Thanks for all the interesting conversation folks.
Check out pg 106 TBB 1 for another good explanation.
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Check out pg 106 TBB 1 for another good explanation.
When in doubt, read the TBB series (there's a reason it's called the traditional bowyer's BIBLE): the answer is probably written out loud and clear somewhere. Tim Baker clearly explains in a few lines what took us 4 pages...
For those who don't have the TBB series yet: it's the best investment in bow-making material you can think of.
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I've read the TBB at least a half dozen times. Sometimes you just miss things and sometimes you just don't understand. I've never been able to relate to the seesaw analogy. I'll have to sit back and think on it for a while. Thanks for the page number.
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Keep in mind that early TBB contain errors, some of them in the musings of Tim Baker.
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yes I think I remember even Tim saying in later volumes that there were some things that had been re evaluated,,but I will say for the time they came out,,,they had great info,, and still do,, back then,,,, there was not the collective knowledge that there is now,,,, its just mind blowing what we have at our finger tips today,, lots of brilliant bow makers that will share knowledge ,,,its amazing,,
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Yeah, ya know the more I look at the info in tbb I referenced, the more I think I see a new twist.
tbb has column 1 as % of limb depth at back or belly and column 2 as tension or compression work done at these depths.
1% 6%
5% 27%
10% 49%
20% 78%
30% 94%
To me it seems it should read as:
% of distance from neutral plain in column 1 = % of work done.
Farther from neutral plain-more work done. The sinew keeps the belly from crushing by moving the neutral plain closer to the belly surface.
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re-evaluated, yes, sometimes a good thing.
I made a comment earlier, that I need to re-evaulate.
sinew is often used to its best advantage with low compression strong wood
is there room left in this thread discuss the merits of using sinew on hardwoods, hickory etc, vs softer woods juniper etc?
looking back over old threads, it seems some folks definitely have some preferences as to what kind of wood sinew works best on.
what are your thoughts on using sinew on a dense wood? is it another way of trapping the back?
DuBois
i had to reread that twice also.....
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eh I'm pretty sure sinew moves the neutral plane farther from the belly (closer to the back)
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Sinew is some crazy wonderful stuff.Maybe someone else can verify this as to happening to them too.While tillering a sinewed bow on the tillering tree removing wood and working my way to my draw weight pulling to my target weight.The amount of set it took pulling was returned after removing wood from the belly.So I quess the sinew was over powering the limb to a certain degree.These things don't happen while tillering till a person puts enough sinew on.Kind of off the subject I quess but the neutral plane movement might have something to do with it.
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Ed, have you ever seen the experiment where a bow that had taken set was sawed down its length separating back from belly?
the back returned to shape because it was being held into deflex by a permanently deformed belly that did not want to relax.
the belly stays the same because the set is....well, permanent. I believe that a bow that recovers from set after a long period of time has had its back pulling constantly, albeit gently, all straightening the bow out.
the sinew in your example started pulling when it began to dry, and that tension is always in the bow. you were removing the most highly damaged/ deformed part of the belly, the surface.
Dubois
He is not saying that 78% of the work resides at a depth that is 20% of the way to the neutral axis.
He is saying that 78% of the work is done between a 20% depth and the surface
the middle third of thickness is pretty close to doing nothing.
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Keep in mind that early TBB contain errors, some of them in the musings of Tim Baker.
Do we know what specific errors there were? just curious so I have a heads up when I read them.
What you have to understand is the only factors that affect the total tension or compression stress the specific fibers undergo, is their distance from the core line from a side profile or how far they bend. If two bows were the same thickness but one had a much stiffer material on the back, like sinew, there still wouldn't be any difference from the compression forces on the belly. The latter bow would have a higher poundage, due simply to the stiffer sinew, not that there was more compression on the belly.
I realize this isn't quite correct, and It is true the stresses on the back or belly depend on the thickness of the limb and how far the limb bends, but those aren't the only factors. The stiffness of the materials play a much larger role than I previously thought. I would like to make a new stab at it. correct me if I'm wrong
So joachimM and Tim Baker in TBB1 were saying that the neutral plane is 2/3 from the belly. If my calculations are correct this basically translates to a compression stiffness of about 1/2 that of the tension (or 50%). In the research paper that Willie posted they calculated the compression stiffness to be about 70% of tension stiffness. Likewise, they found that the neutral plane didn't shift as much as 2/3. It should be kept in mind that the difference in wood species between their compression and stiffness is going to very quite a bit. Would It be a good generalization that the compression stiffness of wood is about 60% that of tension? This is the average between the 50% and the 70% from the two sources.
As far as neutral plane shifting is concerned, the side of the plane which is bigger will undergo more tension or compression. The neutral plane itself will shift towards the side that is stiffer. Therefore the other side will be bigger and stressed more. Wood is stiffer in tension so it shifts closer to the back. If a laminate bow had a stiff wood on the belly, the plane will shift towards the belly thus stressing the back more. Additionally, if you have a less stiff material like sinew on the back the plane will shift towards the belly. this is because the belly wood is stiffer than the sinew. Although it may not be stiffer since the compression MOE of wood is about 60% that of tension. So a 7 GPa MOE for sinew will be stiffer than the belly stiffness of yew (9.6x60% = 5.76 GPa). Then again not all sinew will be 7 GPa in stiffness, the low end of sinew is 2.7 GPa which is much less stiff. So really it's just a big "depends", but I think it's safe to say it will most likely be less stiff, thus shifting the neutral plan towards the belly. However, the neutral plane will also shift towards whichever side you add material too. Therefore, like Joachim said, the shift towards the belly from sinew's less stiff properties is often offset by a shift towards the back by simply adding the material.
So I will try to translate that to composite application. Any add-ons will aid the side it's added on to for two main reasons. First is because the outer fibers do most of the work and the add-on's are more likely able to handle that stress. Second is because simply adding on any material will shift the plane towards that side because thats where you made the limb thicker. There is however, a third factor that affects the bow. Depending on the stiffness of the add-on material, it will stress or relieve stress to the opposite side. for example, a less stiff material may unstress the belly, while a stiffer one will stress it. The same is true with add-on belly material like horn.
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eh I'm pretty sure sinew moves the neutral plane farther from the belly (closer to the back)
Loon
imagine gluing a 1' x 1' x 60 strip of styrofoam to a steel band of the same width and length, and bending like a bow.
if the styrofoam is on the back, its gonna stretch on the outside before the steel compresses. In actuality the steel will shorten, but very very little.
flip it over and put the steel on the back and the styrofoam on the belly. Again, the styro will make the adjustments, while the steel stretches very little. the neutral plane (the place in the cross section where the length does not change), is very close to the glue line in either orientation. If the strip was just the styro alone, the NP would be in the center, but the addition of a weaker materiel on the outside of the bend, moves the NP towards the stiffer materiel, on the belly.
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greg
the discrepancies you note between data are valid. It is generalized by many that wood is twice as strong in tension as compression. There has been very little comprehensive testing of wood in pure tension, because there are no real applications for using wood in pure tension. An example would be to design a wood member for lifting. The extra reinforcement needed for fasteners and glue to attach the member to something else, in order to realize the full tension qualities of the "wood cable" are impractical. As wood is most often used in compression or bending, and since compression limits almost all bending applications , the research is just not there. Some theorize that the difference might be as high as three to one. Comprehensive tests on high quality wood is of interest around here sometimes, but wood like that was in the paper, was typical lumberyard stuff that was kiln dried and might have been harvested half rotten, bug eaten or run over by log skidders, all the defects that have to be considered when rating for construction grade purposes.
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willie...I've seen sinew literally delaminate healthy good red cedar before while bending.It also chrysalled a black cherry bow that was into too much reflex also.I've seen bamboo crush pecan but not breaking the bow.Just leaving a useless ripple on the belly with a hinge in the limb.You could very well be right saying the neutral plane moves to the stiffer material.I'm sure many others have memories of different experimental bows not working out they could mention.
gfugal....Your analogy in your last paragraph rings home true to me in reasoning from making bows.I've seen bamboo probably too thick crush the belly of elm because it was too stiff of material.What is said it over powers it.Sinew being less stiff would'nt near as easily.Density difference cannot be the determining factor either between the two.It's the elasticity of sinew that is the difference.
The last few years I've had good success sinewing hickory.To me more of an imbalanced type wood naturally tension versus compression.It may very well be why sinew is such amazing stuff.It does'nt seem to overpower any wood that I know of in my experience.Unless it is used to put certain woods into designs they can't handle.As far as where & which way that neutral plane shifts I don't have a comfortable hold onto that yet really.I go with what works.I don't worry why.I probably should.I just let time tell me through the school of hard knocks breaking and making bows from different woods.
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I will take the School of hard knocks knowledge every time over theory , only because its realistic I have read every bow building book I can get my hands on & it seems you always find 1 guy says this as gospel & then another guy says somthing that disputes that but when some body that I trust says I tried this & it didnt work or it broke ,Im all ears I think practical application knowledge is far superior then theory ,Im not saying theory isnt practical Im just saying one way is superior in my mind but thats just me.
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"Dubois
He is not saying that 78% of the work resides at a depth that is 20% of the way to the neutral axis.
He is saying that 78% of the work is done between a 20% depth and the surface the middle third of thickness is pretty close to doing nothing."
Thanks Willie, this makes sense to me now.
I agree with SB and Beadman on hands on experience over theory. I peek at theory and then jump in and make my own observations and mistakes. And these mistakes are a lot of fun even if they do hurt once in a while.
experience/experiment I don't speak Latin or any of that fancy stuff but there must be a reason these are so similar in sound.
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I forgot Explossion
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LOL
News update: another OOPS
experiment results in explosion, and Dubois experiences an extra 30 days added to his banishment in the garage
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Hey, I'm kinda enjoying the garage
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I think research is a very good thing.Don't get me wrong,but a person can't be afraid of a bow breaking in this hobby.It's gonna happen.Seems even when a person gets to know a wood after making enough out of it a person tries to push the envelope at times and that takes planning etc. too.Does'nt have to be that way.It's just an individual thing I guess.
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Getting a bit off-topic, but still:
the relative strength of back and belly (including sinew backs) tremendously depends on relative humidity, and on how different woods react in tension and compression forces to such changes.
Note the below graph from the wood handbook:
A: tension strength of wood peaks at 12% MC, and decreases at lower MC and higher MC
C: Compression strength of wood increases with decreasing MC.
The 1/3 2/3 rule of thumb (rule of thumb, not the absolute truth) holds for regular 12% MC, no heat-treated bellies. Some woods are stronger in compression, there it will be closer to 40-60 at 12% MC, and it may shift to 50-50 at lower MC, and even 60-40 at very low MC.
That's why bows gain poundage at lower MC, and break at very low MC: the belly overpowers the back.
Most of the time, the back overpowers the belly, and we get set. A bow with set is still a bow. In reverse, a belly can only overpower the back once...
Sinew, however, will behave in tension like wood in compression: its MOE (stiffness) decreases with MC.
Sinewing a bow is like trapping the back, but in a safe way: you make the back surface weaker, hence the belly is working less. In a trapped back, the neutral plane moves towards the belly, relative to an untrapped back. It's safe because it's darn difficult to break sinew. If, however, the sinew layer is too thin, you'll still break the back when the wood fibers underneath the sinew are overstretched.
If you sinew an existing bow, the neutral plane will shift a bit towards the back. But not as much as it would for a same draw weight all-wood bow to which you would add a wood backing. The reason is that nowpart of the draw weight comes from overcoming the shrinkage of the sinew which put the belly under tension. This is similar in theory to a one-sided perry-reflex. (not that this clarified anything ::) ::))
If you really want to know how things work the way they do, walk the walk: perform predictions on how something's supposed to work, make bows (or test samples) to test these predictions (not one of each kind, but at least three), and see if the predictions worked out.
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wow nice,, I am learning a little at a time as my old brain will obsorb,,its nice to know some of the whys,,thank guys,,
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I think reserch is great also ,one of my favorite things to do when I cant work in the shop but Im just saying when there is a contreversal subject I will take the boots on the ground advice over theory !
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To most osage is the best balanced type wood that is out there.Getting bored making the same thing over and over from the same wood stiffels my enthusiasm really so investigating and trying different type woods with different types qualities and designs helps to make a better bowyer far as I'm concerned.Usually other woods besides osage are a bit more touchy and not as forgiving.Sinew can make less forgiving woods up to the standards of osage I feel.Osage is such a forgiving type wood of mistakes but.....it will break yet if certain rules are not heeded.
Hope this is'nt off the track too much of the subject but it all makes a difference.
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To most osage is the best balanced type wood that is out there
and I suppose yew is right up there somewhere, too.
With these proven woods, are the exceptional qualities on account of the balance between tension and compression?
Or could it be a matter of the tension qualities being exceptional, or is it the compression qualities?
I guess if osage and yew perform well as a belly wood, with a variety of different stiffness backs, then the quality could be said to be in the compression side.
Don't see many folks trying yew sapwood or osage for backing different belly combos, like you do with sinew, but you never know until you try!
"boots on the ground" experiments that break bows are certainly the best teacher, some of us just want to understand why, after the explosion or slug gets consigned to the kindling pile.
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Del has done at least one with a yew sapwood backing. I seem to remember it working well. I think "good wood" is a serendipity thing. There is every combination of features in the wood of the world. A few of them have to work out good for bows. Osage and yew just happen to top the list. I don't think it's just tension or compression, it's the combination that makes it work.
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I think quite a few other woods are also balanced woods relative to their own strength. Or they can be readily balanced with heat.
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To most osage is the best balanced type wood that is out there
and I suppose yew is right up there somewhere, too.
With these proven woods, are the exceptional qualities on account of the balance between tension and compression?
Or could it be a matter of the tension qualities being exceptional, or is it the compression qualities?
I guess if osage and yew perform well as a belly wood, with a variety of different stiffness backs, then the quality could be said to be in the compression side.
Don't see many folks trying yew sapwood or osage for backing different belly combos, like you do with sinew, but you never know until you try!
"boots on the ground" experiments that break bows are certainly the best teacher, some of us just want to understand why, after the explosion or slug gets consigned to the kindling pile.
Yes willie it's the balance of tension to compression in the wood itself on their own.Pat M's right too that balance can be played with on most tension strong whitewoods.
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I've personally never seen the need to heat treat a hickory that's going to be sinewed anyway though,but on their own without sinew yes.Many fellas can make a good hickory bow just by trapping the back too.Again balancing out those 2 forces of tension and compression.
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I guess it makes sense to see if one can make a stiffer belly by heat treating on a known tension strong wood, that can take the extra strain.
But what about applying sinew. Are there any basic rules of thumb about how thick it needs to be?
getting a good balance with juniper might be a lot different from getting a good balance with hickory.
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Wille thats a great question about the thickness,,,
most people will say,, well about so many layers,, but a layer can vary in thickness dramaticly,,
there is just not a very good rule of thumb that I know of,, hope someone can chime in,
I think I read somewhere,, not to exceed 25% or the thickness of the wood,, its really hard to judge,, cause when you put it on ,, it looks soooo thick, and then shrinks to almost nothing,,
I started weighing the dry sinew before I put it on ,, just so I have a general idea how much is going on there,,
I usually start about 1000 grains on a bow that is 55 ish,,
and you could easlily go more,, but then there is a point of diminish return where the sinew would be to heavy to increase your performance,, I dont know where that is, I plan on doing some bows with too much sinew just to see what happens,, :)
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Yes that could be true willie.I personally hav'nt worked juniper.Many do on here though.As for hickory alone 2 to 2.5 ounces on 1 and 3/8" wide parallel limbs to midlimb on a 48" long stretch including handle and fades reflexed to 6" will give you 4" most times of held reflex with good tillering and tapering.At least 1/8" thick dried cured sinew.A 1/16" thick layer of sinew does'nt do much but protect the back from breaking and will give too much in set for this design to hold all that much reflex.That's on a 60 to 64 inch bow.I don't sinew the tips last 8".It'll give you upwards of almost 20 pounds.So you can factor that into making a bow of 25 to 30 pounds[tiller it to brace and then to a 20" pull to get a good reading on how strong the bow is.Put your sinew on.Reverse brace it and let it cure a good 2 months and end up with finished bow of around 45 to 55 pounds.The hickory will more than likely take a slight set while pulling to 20" but that will be negated after the sinew cures.You can heat treat the belly before sinew too but then your poundage will go up from heat treatment on hickory a few pounds.Many ways to go but it makes a terrific bow.Think you could do it with hackberry too.These numbers can be adjusted too to suit your needs.
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willie and gfugal, have you guys done a sinew backed bow yet?
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Thanks Ed
your approach seems to have a lot of merit, if I understand you correctly. Enough sinew to prevent set, (can I also assume that any more than whats needed to do that job, would be heading towards too much?)
Taking that for a guide, would one think that the amount of sinew needed to prevent set, (can that be the" balance point"?) would be less for a belly wood that was not as stiff and had a MOE closer to the stiffness of sinew?
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I have only made 2 sinew bows one a thin D type bow that I only used 750 grain which in hind site probably to little & the other was a wide maple bow & used around 1100 grains which seemed about right, on my current build which is a 57 in. bendy that is going to have about 5 in of reflex I'm planing on using 1000 to 1100 grains only because that seems to be the comon denominator with the guys that keep track of there sinew weight & bows posted here , I find it interesting that the guys that have made a lot of sinew bows always state sinew used between 1000 to 1100 grains 2 ex samples in posts above.
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Set is still gonna happen but to a lesser degree with enough sinew.Look at it this way.Point being with sinew is you want to make it work more to it's abilitys.If you put more on reflex it more.Otherwise your carrying dead weight that is'nt working enough.If a person puts a strong 1/8" thick cured as a starting point to see some benefits from it it'll handle the reflex previously talked about.Putting more on goes in stride with more reflex.Make it work!!!
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willie and gfugal, have you guys done a sinew backed bow yet?
I've made two. The first picture is the very first bow I made. It's working limb juniper branch, thats 37 inches long or so. It wasn't a big branch so it had a high crown, so I was suprised that i got it as far as I did. It's at a 23 inch draw in this pictureI sinew backed with on layer and surprisingly it had little set. I wasn't satisfied with the draw weight though, so I put another layer of sinew on to increase it. It did make it stronger but unfortunately it altered the tiller and I didn't think to check before I brought back to full draw. It broke.
The second is a douglas fir that I put two layers of sinew on. I actually, put a bowstring sized cable on the back made from polyester, and seccured it down with thread and the second layer of sinew. You can see in the third picture if you look closely the outline of the cable underneath the sinew in the closest recurve. I got it pulling to 27 inches despite being 43 inches long. It has bad string angle though so it stacks, as well as quite a bit of set.
As you can see I've really been testing the limits on how far these bows can bend. Mainly because I didn't know any better at the time, secondly because I like short bows, and thirdly I have a long draw of about 31" so If I could get these shorter bows to draw that far then In the future hypothetically I should be able to get an average length bow as far as 31-or-32 inches. I didn't know as much about string angle then so I've learned that they need to be much longer, or have large siyahs. But I've also learned that sinew can really protect the back of a bow and allow the design to be much more stressful.
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So just get going on a slightly longer bow with siyahs. I posted a picture of exactly what you are looking for. You may be overanalyzing things now.
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Amazing over draw your getting.Looked like good tiller too.Sorry it broke for ya.Could of maybe helped for it to be a wider bow to help carry the load,but we work with what we got I guess.Ishi made some powerful sinewed juniper bows with a lot of reflex.
The tips flipped back help yes for smoother draw and less stack towards the end.Here's a pic of a current bow in progress curing.It will look a lot like your full draw picture when done.It's 58" long.Hickory/horn/and sinew so I expect it to hold a lot of the reflex as one's like it in the past I've done.A little more sinew and refllex I expect to put on this one yet.
(http://i920.photobucket.com/albums/ad41/Beadman1/DSCN1512_zps0e5hqvko.jpg) (http://s920.photobucket.com/user/Beadman1/media/DSCN1512_zps0e5hqvko.jpg.html)
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Ed
I don't know why people refer to a "balance point" when matching a backing with belly, perhaps it goes back to the Baker "see-saw" analogy. possibly implying something inherent in the back or belly properties need to be matched. I like the idea of.... it's not too much, if you are bending it enough :)
Hmm... sounds kind of condescending to my ears, Pat. Why do you think Greg is over-anylazing? that's often said when work gets stalled, but I don't see any indication of that happening.
As for my self, Not yet.
Is that the answer you are looking for?
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Ed that looks like a supper model setting in that chair Bow porn....lol nice pic I know I have over thinked stuff in the past but have under thought & paid the price too ,while where on this topic does any body have a preference for a certan sinew preferance elk,moose,horse,white tail etc ?
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StickBender....It's not got a string on it yet and can't be called bow....lol.Personally I like the longer 6" to 16" long strands from my elk legs.Sometimes longer.Moose too.I use my shorter strands of deer leg to fill in a lot.It's all good really.Gotta try horse sometime.Heard it's pretty good.Backstraps' good too but I have a hard time during the presoak to get it soft enough but when a person does Pat M's method of wrapping and heating that usually softens it up pretty good for a nice smooth clean job.Like the length of backstrap though.
willie...The whole balancing thing of back to belly in forces is to get away from too much set and just plain good tillering and design.
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Not at all but it's the answer I expected. ;) I would say he's over-analyzing the theory without pursuing the basic execution. Those two bows were a while go.
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gfugal......On your other bow the polyester cable you put on underneath while probably in your mind gave you some sort of security or poundage hike actually I think took set and did not come back as sinew will.Best to leave synthetics out of the equation and just go with sinew alone.
Linen string backed bows will take set too just like wood.Any fibrous type back will but it can increase poundage and make them practically unbreakable.
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Not at all but it's the answer I expected. ;) I would say he's over-analyzing the theory without pursuing the basic execution. Those two bows were a while go.
I'm pretty new to bow building, but I did research a lot before I started. Sure I don't have as much experiance as others, but of the four i've built all have been backed with 2:4 ratio for sinew. That's more experience on this subject than most beginners, or even some veteran bowyers who've never backed a bow. It's not near the experience you have, but I don't think you need a lot of experience to theorize.
There's two ways to learn. The hard way through experience, and the fast way through research. Ideally you need both to really get going places. Research alone won't translate to a bow, you actually have to make them. On the other-side, making without researching is just wasting your time in my opinion. You can spend hours on hours making something, not to mention the materials, only to have it break and learn a lesson you might have found out with some research. I don't prefer that, to me it's almost like pounding your head into a rock. As long as your not halting your work to learn what harm is it doing?
Needless to say I'm not stalled. Since I finished my first bow I've immediately moved on to the next. Again I go to work and school full time. I was able to push out a bow in the month of December because of Christmas break. I don't have that time now. What I do have is down-time at work and I, fortunately, am allowed on here to research, so I might as well utilize that time. My execution will get better, but do you feel it was subpar in someway? Is there something I said that makes you think I don't know what I'm talking about? If so let me know and I can examine it, don't attack my experience.
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OK but would you consider those a success due to your previous research?
I guess how we measure success varies.
If you are happy with your workmanship and are comfortable with your knowledge, that's all that matters.
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OK but would you consider those a success due to your previous research?
I guess how we measure success varies.
If you are happy with your workmanship and are comfortable with your knowledge, that's all that matters.
I am proud that I was able to get bends like that without horn. Not a lot have people have done that on here. That’s not to say that I think they are the most well-designed bows or the fastest, but they are bows. I didn’t pick those designs because of my research, rather it was out of necessity of material, and not knowing any better. So if anything, more research would have inspired me to do a different design. I guess I don’t know what thing I said is contrary to what others have shown through experience. But I would agree I need more of it.
So just get going on a slightly longer bow with siyahs. I posted a picture of exactly what you are looking for. You may be overanalyzing things now.
That’s good advice. I don't want to seem like I'm trying to contradict you. I will attempt it soon. I remember that picture and I thought it was sweet. Thanks.
Ed that looks like a super model setting in that chair Bow porn....lol nice pic I know I have over thinked stuff in the past but have under thought & paid the price too ,while where on this topic does any body have a preference for a certain sinew preferance elk,moose,horse,white tail etc ?
Haha that’s what I thought. It looks like its in the middle of some abandoned wherehouse with a spotlight on it. Is that your work shed? But it’s a sick bow. Hopefully you will get a good force curve out of it.
gfugal......On your other bow the polyester cable you put on underneath while probably in your mind gave you some sort of security or poundage hike actually I think took set and did not come back as sinew will.Best to leave synthetics out of the equation and just go with sinew alone.
Linen string backed bows will take set too just like wood.Any fibrous type back will but it can increase poundage and make them practically unbreakable.
I got set even before I added the cable. Here’s a picture of it before the cable and second layer of sinew. I agree with you that it's going to stress the belly more, I just don’t think that rules out the use of cables on wood bows. You don’t have to put it under the sinew. It was just a unique Idea I had, but I believe it would perform better if it wasn’t glued in place and was allowed to return back to its original shape. Don’t base a cables effect from my bow. It was going to get set no matter what because of the overdraw. I’ll have to experiment with a longer bow. You also mention that fibers, whether synthetic or not, get set? I wonder if that set is just the re-positioning the fibers after its stretched out for the first time, or if its because it's stretched past its yield point. It was mentioned some time past on here that flax gets stiffer the further it's stretched and doesn’t behave like a spring in hooks law. I’ll have to look more into that.
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You may be tricking yourself a bit by measuring success by a lot of bend and not breaking(right away). Definitely few people want to go for extreme bends in wood for various reasons but backed wood can hold together under ridiculous bends. Especially less compression resistant woods and light draw weight.
That doesn't make it a viable bow though.
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You may be tricking yourself a bit by measuring success by a lot of bend and not breaking(right away). Definitely few people want to go for extreme bends in wood for various reasons but backed wood can hold together under ridiculous bends. Especially less compression resistant woods and light draw weight.
That doesn't make it a viable bow though.
I don't think you can judge success off of one factor alone. Is how far a bow can bend determine success? No. it doesn't but I think it is a factor, along with aesthetics, stability, durability, speed etc. I think the best factor is the speed it can shoot an arrow. these bows weren't the fastest so does that mean they weren't successful. Maybe, but they still teach us things, especially with a topic about sinew. So take them for what they are. I'm not going to be ashamed of them.
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I wonder if that set is just the re-positioning the fibers after its stretched out for the first time, or if its because it's stretched past its yield point
possibly both, and there is also creep, a third property of fiber to consider.
ht tp://samsonrope.com/Pages/DemystifyingElongationandCreep.aspx
traditional cable bow archers had twisting levers to make adjustments
https://www.archerylibrary.com/books/mason/north-american-bows-arrows-and-quivers/docs/lxxv.html
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I have nothing against cable backed bows.In realize they are out there.The polyester cable did not return the bow to it's original form though because it took set is my point.Along with the fact that fibrous material does not return like sinew in a matrix of hide glue on the back of a bow.I doubt very much it would of returned the bow to it's original form on top or underneath sinew.Nice experiment though.You learned something.
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The old pre-stretched silk backings did in fact function like sinew. That was through some skillful manipulation of the fibers and the binding glue.
The beauty of sinew and hide glue is that it does almost all of the technical work for you.
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I did'nt know that about silk.I've never researched any about it I guess to begin with or really considered it.I was thinking vegetation type material at the time I guess.That'll teach me to never say never.Silk is fibrous but from a worm.Sinew is fibrous but from a deer and the like.
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Pat, just curious if you know whether the silk application was done in single or multiple layers?
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I'll find some of the details. It was a single pre-fabbed strip that was applied in one go. Not sure how the strip was first laid up though.
But it definitely countered Tim Baker's thoughts on silk.
This is mostly because you have to consider fibers and their binding matrix together. People love to say carbon is really stiff for example. But it isn't until you saturate it with epoxy and cure it.
Here is the link to the patent: http://w ww.freepatentsonline.com/2285031.html
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each strand is pretensioned in the matrix
from the patent description....
When the sheet is manufactured the strands are placed on the drum under tension and after drying they will remain under a pretension of at least one half inch in a yard (36 ins.), the strands being so held by the glue as to give. this effect. Such a sheet when applied to a bow, even without additional tension is much superior to other forms of backing material.
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I know, I said that before I located the link and checked. ;)
There is a popular mechanics article from the era showing how the strips were tensioned and applied.
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the drawings are in a pdf that you can download at the url you linked.
the filaments were continuously and individually prestretched before manufacture into a backing, and this can add up to an amount incredible of stored force in the matrix. The cured backing was technically post-stretched before gluing to the back.
not quibbling about the use of words here, only making clear that the fiber was actually stretched three times (if you consider the bow at full draw.)