Primitive Archer
Main Discussion Area => Bows => Topic started by: joachimM on February 12, 2015, 04:14:53 pm
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Hi Folks,
though this bow here was broken a few days ago (due to a stupid mistake), I still want to share a few thoughts on it, mostly because it refused to take more than a few mm of set and was made from scraps.
Specs: toasted hazel (Corylus avellana) 137 cm ntn (54”), 7 mm thick throughout working section (0.275”), to 8.5 mm thick (0.33”) in last 10 cm (4”) to nocks. Naturally set back in the handle, yielding 2.5 cm (1”) of net reflex. Pyramid design, 43 mm wide (1.7”) at fades to 10 mm (0.4”) at nocks. Each limb was 56 cm (22”) long, 25 cm (10”) stiff handle and fades . Prior to backing: 21# at 27"
Backed on each limb with 10 m of rough single ply sisal cordage that I recovered from hay ballots (cut into 25 cm pieces, washed, combed) and glued with gelatin (c. 9 g of gelatin per limb). Backing c. 3 mm thick, slightly crowned.
The stave from which it was made had been attacked by grubs, so both limbs had two holes (3-4 mm diam) going from back to belly, but which were filled with epoxy. Still, I wanted to try backing it.
When I approached 28# during draw-weighing of the backed bow the string slipped off one of the nocks and the dry fire caused one limb to break at the belly. Draw weight: close to 40# . Shot 330 grain arrows 210 m (230 yd) far. My guess is that this bow, had it not dry fired, would have shot around 175 fps at 10 gpp.
The picture shows rather extreme floor bending and the profile just following that. Despite this crude maltreatment (over and over again), the limb refuses to take more than a few mm of set. Although the bow is useless now, it has shown me the potential of plant fiber backing. No sinew pounding for me in the near future.
Joachim
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That's a bummer about the bow. Thanks for the info on sisal- it sure is easier and cheaper to get than sinew or flax.
c.d.
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I like plant fiber backins a lot, and I still advocate linen canvas, (despite a few draw backs). I apply it with a jig that cranks the bow into reflex first, to pull it tight, and love to draw on it.
The two backings are very different, though. I'm amazed at your hazel success, for sure, but sinew stretches 10% or more of it's length, and plant fibers just stay put and stretch hardly at all. So, I use them for different applications
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The two backings are very different, though. I'm amazed at your hazel success, for sure, but sinew stretches 10% or more of it's length, and plant fibers just stay put and stretch hardly at all. So, I use them for different applications
I often have the impression that sinew backings without a horn belly is like a monkey with a golden ring: you'll never stretch the sinew on such a bow for more than 2, max 3%. And if you would, no belly could stand that compression. Plant fiber backings can stretch up to 2% if I recall well, so I don't have the impression that one ever really needs the sinew's full capacity, unless on sinew-wood-horn composites.
Probably the most useful property is that it shrinks when curing, so you pull the bow into reflex. If, as you do, you reverse bend the bow, and add linen, you achieve about the same result.
And don't be mistaken: these plant backings do stretch. I recently had a similar argument about bamboo not stretching (on paleoplanet): bamboo does stretch, just like any other bundle of cellulose microfibrils, it's just very strong in tension, especially given its rather medium density.
I find woven backings much harder to apply than bundles of fibers, but if you have a good technique for doing so, is there a post where you describe it?
Joachim
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The actual outer surface of bamboo is denser than 98% of the woods found in Archery.
Pretty sure sinew can be stretched more when used properly on just wood.
I hope you don't think your simple test proved inconclusively how much bamboo stretches on a wood belly. ;)
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How well do you think that yuka would work for a backing? We have quite a bit of it growing around one of our sheds and have been thinking about using some of it for something. I sort of want to try backing ERC with it since I have a bunch of the stuff. This will probably be a spring or summer project since I already have 3 bows going now.
Kyle
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I have a short, light weight rhodedendron bow with 8" of reflex that draws 28"+ and keeps 5" of reflex. It has one thin layer of sinew, no horn, but the belly is concave.
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If you get a good piece of hazel it is absolutely bombproof. I have a short, de crowned test bow out of it, about 56 inch or so......it will go to 36 inch draw and no set.....seriously i'm not joking. I couldn't draw it any further because my tillering board bottoms out.On the other hand some hazel is lighter than balsa! That little bow is beyond nuts :o :o :o
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Would natural Jute twine work as a backing material? ???
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Jute should work just fine, but someone needs to try it.
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I'm working on a Yew stick which I've reduced the sapwood on. Inadvertently I have cut through a few pin knots so I think it could use backing. I also have a big roll of jute twine which needs using. So I think I'll try putting the two together and see how it goes! :)
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Hemp, jute, and sisal all work. Jute and hemp are the best in my experience. Hemp being the best in my opinion only because its softer. I have repaired broken backs with it before. Works great.
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I could be wrong here but my understanding is that sinew is more elastic, ie stretches further and thus is less likley to over power the belly (and cause chrysals?).
That said cutting the fibers into shorter segments may allow them to slip against each other to some tiny degree and give a similar or better result to using sinew.
That was going to be my next experiment in backing.
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"I often have the impression that sinew backings without a horn belly is like a monkey with a golden ring: you'll never stretch the sinew on such a bow for more than 2, max 3%. And if you would, no belly could stand that compression. Plant fiber backings can stretch up to 2% if I recall well, so I don't have the impression that one ever really needs the sinew's full capacity, unless on sinew-wood-horn composites."
I admit to having very little experience with sinew on bows, but I will agree that the absolute best use of it is likely on Asiatic composites. On the other hand, I have the impression that wood bellies EASILY resist the compression induced by sinew backings. Sinew is a very "soft" backing. It stretches a lot, and quite easily. I always understood that a sinew backed bow stored energy IN THE SINEW, as it stretches, and the very fact that it does stretch means the belly is forced to compress less. My few experiments with cable backed bows bears this out to me.
The part about the sinew not experiencing ENOUGH stretch is totally valid. This why short, reflexed bows, or those allowed to dry into reflex are the most appropriate designs. Those designs make the sinew work. A big flatbow absolutely will under - stretch the sinew.
On the other hand, bamboo and hickory backings "overpower" some woods specifically because they are so stretch resistant. Plant fibers WILL stretch a little, but they resist it, Baker says they "stack" before they break, and they don't stretch far.
"Bamboo does stretch, just like any other bundle of cellulose microfibrils, it's just very strong in tension, especially given its rather medium density."
The very outer surface of most bamboo species is MUCH heavier than even the more common tropical hardwoods, though. I had some tropical bamboo from India once over 1.30 SG.
"I find woven backings much harder to apply than bundles of fibers, but if you have a good technique for doing so, is there a post where you describe it?"
Nothing to it. I rough tiller a bow (mostly done this with board bows, of course) ad use a big C- clamp to hold the handle down to a 2x4. The key is the clamp goes under the board and clamps the sides of the handle. I place blocks under the tips to push the bow into reflex, as much as I think it will take. Then thin some TB III with just a splash of water, paint it on the limbs as a sizing coat. Let it partly dry. I cut a linen strip as wide as the bow's widest point.Then slap down a layer of glue from the bottle, smooth it evenly, and lay the strip of cloth down end to end. Finally, I use the thinned glue to moisten the fabric so it will relax and pat it down against the limb, smoothing and lubricating the fabric as I settle it down with a finger or paintbrush. It has never lifted on me while drying, except once on a crowned back. When dry, I trim the sides with a knife and file the edges smooth to the limb edges.
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If you get a good piece of hazel it is absolutely bombproof. I have a short, de crowned test bow out of it, about 56 inch or so......it will go to 36 inch draw and no set.....seriously i'm not joking. I couldn't draw it any further because my tillering board bottoms out.On the other hand some hazel is lighter than balsa! That little bow is beyond nuts :o :o :o
That is very interesting. I have a handful of hazel staves I haven't used, but they seemed so light, I was saving them for midweight, like neighborhood teenager bows.
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Joachim have you ever built a sinew backed bow?
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When sinew streches it snaps back, when plant fibers used in the manner you are useing them may stretch a little but aren't going to snap back, take a rope for example when new it stretches a lot but stays stretched out
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Sprinbuck: so on bows with relatively low moduli of elasticity (such as yew, ERC and osage, incidentally) sinew, having itself a low MOE, would be a good backing, right?
On stiffer woods, plant fibers would match better, and on the very stiff and dense like ipe it's best to use very strong and stiff backings like hickory and bamboo.
No surprises to all the experienced bowyers here (and no i havent sinewed a bow before, never had the opportunity to work with bow woods i deemed would benefit from that), but stirring up things ensures you get insightful replies >:D
Has anyone ever plant fiber-backed yew, osage or juniper? Maybe nobody does it because it doesnt work (likely), or because nobody does it...
I'm gonna remove the fiber backing of the abused limbs and examine if there was set in the belly that may have been concealed by the backing keeping it straight.
Joachim
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I often times wonder if we as bow builders don't do things because we don't do things. It is something that we have been trying very hard to undo at my work. Somethings that we have been doing for years aren't the only way to do things, and all it takes is trying to do it differently to learn that we COULD do it differently, we just chose to play it safe and not. I play by the rule of "What works for you and doesn't work for me isn't wrong, it is just different." It is hard to let go of how "it is supposed to be done", for "if it works, and gets good enough results than why not?"
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My hay come with some type of synthetic. I think it feeds through the baler better, but I still see the natural stuff at TSC sometime.
Jerry
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I removed the sisal backing from this hazel ex-bow to examine if the fiber backing just prevented set in the belly to show (keeping it straight). That wasn't the case. The bow still had all of its reflex and showed no sign of any set.
After I bent the still intact unbacked limb as I did in the pics, it took an immediate and rather permanent set.
Some of you may have expected this, I didn't...
Since the plant fibers were taking most of the tension, the hazel belly, so I believe, should have experienced more compression than in an unbacked version (action-reaction). So I expected it to take no more set than with the backing still on.
Anyone has an idea about the physics behind how a stronger backing can actually protect a belly, or other hands-on experience on this?
Joachim
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Joachim
I have some ideas about what might be happening, but is does not involve physics behind how a stronger backing can actually protect a belly.
Can I ask a question or two?
how did you remove the backing?
is the belly with set just as stiff as a piece of unworked hazel of equal thickness?
can you elaborate a little more about your conclusion... showed no sign of any set.
willie
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I shortly steamed the entire bow 15 min and removed the softened backing, nearly as a whole lam.
I then set the stripped bow aside for two days in a heated place to lose excess moisture from the steaming and get back at 12-13% mc.
The stripped bow indeed seams as stiff as before backing.
My conclusion concerning set pertains to the bend radius and the position of the neutral plane. With a backing, the bow is thicker and the belly surface further from the neutral plane. This should expose the belly to more compression for the same bend radius, yielding more set. Instead it took less set with than without backing
Did this clarify things?
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Joachim-
thanks for your patience and the clarification. I had initially thought that maybe re-introducing moisture might account for some of the characteristics you reported, but you have already taken this into account. One possibility is that the backing may not in fact be stronger than the belly. Could it be that the backing you removed was doing most of the work of the limb and the belly strain was never was never beyond it's limit because the neutral plane was closer to the belly? When you made the bend without the backing, you were bending a limb with a much stronger back and induced set. Your bend radius in the pics look like they would crush the belly of even a very thin limb.
quite interesting testing
willie
edited after rethinking the possible locations of the NP
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I often times wonder if we as bow builders don't do things because we don't do things. It is something that we have been trying very hard to undo at my work. Somethings that we have been doing for years aren't the only way to do things, and all it takes is trying to do it differently to learn that we COULD do it differently, we just chose to play it safe and not. I play by the rule of "What works for you and doesn't work for me isn't wrong, it is just different." It is hard to let go of how "it is supposed to be done", for "if it works, and gets good enough results than why not?"
Excellent post, very true! Although most of the "rules" hold true, there are many variations in getting to a complete bow. Everything is wrong when YOU can't achieve something, not true for the next person. Experiment, make new ways of doing things.....or what's the fun? ;) ;) ;)
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The actual outer surface of bamboo is denser than 98% of the woods found in Archery.
Pretty sure sinew can be stretched more when used properly on just wood.
I hope you don't think your simple test proved inconclusively how much bamboo stretches on a wood belly. ;)
You're right that the outer surface of bamboo is really dense and strong. If you use that as a backing, the neutral plane will come very close to the backing in most cases, as a result of which it won't stretch a lot.
Now back to the plant fibers: flax has a SG of 1.4 to 1.5 (just like most other plant fibers), and can stretch up to 1.8% (twice as far as most woods), but some sources mention 4% (but I doubt that's entirely elastic stretching). It has a very high modulus of elasticity (MOE), meaning it requires a lot of force to stretch, unlike sinew. So if you use sinew as a backing, you need a lot more of it to take the most tension of the back of the bow. Since it also has a higher SG than wood, you add more mass to the bow than if you were to use plant fibers (and achieve the same increase in stiffness of the bow, as you would need less plant fiber backing to achieve the same goal).
Some time ago I estimated the max strain of sinew at the back of a 90# turkish horn-wood composite bow. This came close to 5%. That's also close to the elastic maximum for sinew (it can take a lot more, but it doesn't spring back immediately beyond this point).
On many sinewed wood bows, the sinew will not need to stretch beyond 2% (I will try to estimate these as well, but need thickness of maximum bending portion to do so in addition to an unbraced and fully drawn profile pic and ntn length), so in those cases you may also consider a thinner plant fiber backing, yielding in theory an overall lighter and therefore faster bow.
Granted, on very short bows the cost of excess mass is much lower than on typical-sized bows, so you might stick to sinew there. The goal of my post was mostly to indicate that there are other very useful and much easier backings than sinew.
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One thing you are overlooking is that a backing is a composite matrix. You have to look at the sum of the parts. Sinew is stretchable in the dry state on its own but I doubt hide glue matches the elasticity perfectly given the predisposition for backing with too much glue to crack when drawn.
You'll also have to do one before you decide on the relative merits and ease of application. ;)
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You're absolutely right that I should try a sinew backing before I make up my mind. But there's just 24 hours in a day, few of which can be dedicated to archery... Next, I don't have staves that one would typically back with sinew (ERC or other junipers, osage, yew, ...) I could try maple. Would need to buy some sinew.
The challenge works both ways: who has backed osage or yew with flax or other plant backings and with sinew? Who can compare the merits of both backings on the same wood? Otherwise, we'd still be comparing apples and oranges.
So far, I haven't seen a lot of these. It seems most folks back yew or osage with sinew
Anyway, my main point was that even junk cordage from hay bales could make a fine backing, and that plant fibers are generally underrated. Let me take back what I said about sinew, till I make a decent sinew-backed bow :)
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Just for your information: the beautiful Osage sinew plains cheyenne bow by Simson (http://www.primitivearcher.com/smf/index.php/topic,50401.0.html) stretches its back at full draw less than 1.2% (on the basis of the crude estimations I could make from the photo's supplied).
So it doesn't take advantage of sinew's capacity to stretch more than any decent plant fibre such as flax.
But that doesn't considered that sinew could give a sweeter draw because of its lower modulus of elasticity.
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" Crude estimations" have no place in proving a point.
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" Crude estimations" have no place in proving a point.
Agreed. There are so many tricks to applying sinew in a pre-loaded fashion while its still wet. Then as it dries it pulls a bit more if your lucky. So the sinew is loaded before the limb even starts to bent to brace, or beyond. Had you actually made a sinewed bow already and felt it wasn't worth it, Id tell you its your own fault and to try again the right way this time. Cant argue with 10,000 years of historical use of sinew on bows.
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Crude estimations, if they are made conservatively, can make a point.
I can't measure the thickness of the bow accurately from the pictures, so I made it conservative. From the pictures, it seems the bow is about 0.6 " thick (I asked Simon about it).
I took the reflex the sinew induced by shrinking into account, and even then, suppose I underestimated the thickness by 30%, the 26" draw won't stretch the sinew more than 1.5% (which is still within reach of flax).
Don't get me wrong:
I don't question that sinew is useful, especially on short bows. What I'm trying to convey is that on many designs on which sinew is typically used, plant fibers may also yield very good results, especially when you pull the bow into reflex before applying the backing. Sinew does that by itself by shrinking. The reason why I think plant fibers may often yield similar performance is that the sinew is rarely stretched more than the plant fibers could take, except for horn-sinew composites.
But I guess my argumentation is futile here against two heavy-weights opposing it.
Still, I'd like to see a comparison between flax and sinew as backing on short wood bows.
Humans are conservative by nature, sticking to what works. Which isn't necessarily what's best. Arguments like "people have been doing so for 10 000 years so it must be the best possible combination" don't convince me. Many ancient bow designs (e.g., the Meare heath bow) were rather suboptimal if you consider the mass principle, and yet they were used (and are still used by some for hunting), because good enough is all you need. You don't need a 175 fps shooting bow if you can kill a buffalo with a 150 fps bow. Maybe it was easier or more convenient for many native Americans to use sinew instead of plant fibers (and they surely didn't have flax).
So the historical argument feels like claiming that a tall pyramid can only be built without wheels, because the Egyptians didn't use wheels ...
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You just need to do your active mind a favor and properly sinew a suitable designed bow or six, then make some deductions. Have you measured the elasticity of sinew vs. flax? Do you know which reacts/recovers quicker?
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joeachim
I have been intrigued by the use of fiber backings and flax is often cited to have good potential. My research has shown that some of the best flax in the world comes from your country, and it seems that flax harvested for other uses may not be as strong as it could be, or the best that bowyers would like have for their use. Certainly the strongest flax would be of interest for string making too.
Have you looked into how to make best use of your local flax, built with/or used flax in your bows or sourced some local flax that might might have been harvested and retted for optimal strength? Perhaps the bowyers in this community would find reports of this type more pertinent than speculations about sinew or some cheap mexican twine salvaged for use in your last bow project.
Just sayin, as there are guys here that would like to get their hands on the best flax in the world if there was a way,
willie
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All plant matter (organic) will dehydrate then slowly desecrate with age. Even if it's sealed. Ask anyone thats braded or twisted up corage for rope. I won't last very long even if it's sealed and protected.
CROOKET ARROW told me a long time ago there's nothing green worth useing for a backing. I never disputed him he's built bows for over 50 years.
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You just need to do your active mind a favor and properly sinew a suitable designed bow or six, then make some deductions. Have you measured the elasticity of sinew vs. flax? Do you know which reacts/recovers quicker?
Is there anyone out there who know which reacts or recovers quicker? Anyone who can compare six decently made sinew-backed to six decently made flax-backed? I have the impression that we're having arguments pro this or pro that, but very few hard facts to compare it to.
I haven't measured the elasticity of sinex vs flax, luckily other people have done so (Dick Baugh measured it for sinew, data on flax can be found easily). This article is informative. http://www.primitiveways.com/secrets_of_sinew.html
So if you want to know: the modulus of elasticity (the resistance against tension, in this case) of sinew is about 3.3 GPa, that of flax is 58 GPa. Meaning, it takes close to eighteen times more force to stretch flax a certain amount than sinew, although the specific gravity of flax is just a bit higher (1.45 compared to 1.3). The sinew can stretch in an elastic manner (though it takes about 10% of temporary set, or creep) up to 5%, flax can do so up to 1.8%. I don't know about the degree of creep there.
So if you back a bow with sinew, you need to put a lot on it to gain some poundage. At the expense of adding a lot of mass too. However, you will be able to bend the bow further than if it were unbacked. The limit is then given by the belly properties of the wood (and the thickness of the stave you're backing). The most compression-resistant woods are junipers (especially eastern red cedar), osage, yew (the usual suspects for sinewing), but also lignum vitae, pear, buckthorn, madagascar rosewood, and a few other species.
If you back a bow with flax, you don't want to add a third of the thickness like with sinew, cos the belly would be crushed. Suppose that you'd normally make a self bow 14 mm or 9/16" thick, then you could take a wooden core half as thick, and back it with a thin layer (1 mm) of flax and still have decent poundage, thanks to the high MOE of flax. The belly is protected against set by virtue of its low thickness (in effect, the neutral plane will be close to the flax glue line, nearly all the wood working in compression.
You could make short bows (50" with 28" draw) in this way. These bows will be much lighter than similar poundage sinew bows, because you need to add only a thin layer (<10%) of the heavy flax-glue combo (compared to a third of the nearly as heavy sinew-glue matrix).
The hazel bow I made (but which broke due to an accidental dry fire): suppose I had sinewed it (nobody in his right mind would do that), it would still have had a low draw weight (<30# according to Dick's info), but it would have become a lot heavier, and would therefore be a rather slow bow. With a comparatively thin layer of low-quality plant fiber backing, I got nearly double the poundage (~40#) and a pretty fast shooting bow.
So it isn't about which backing is the best. It's about knowing how to use each of them, depending on what your purpose is and what wood (species and thickness) you are gluing it on. That will give you the best backing for each specific bow. On PA, I rarely read about plant fiber backings, and the default value seems either hickory/bamboo or sinew.
As for sinew: when stretched to 5%, as in this bow for example (http://paleoplanet69529.yuku.com/topic/60635) it requires as much force to bend to its elastic limit as a similar thickness piece of a heavy wood species like Ipe. That is when the ultimate properties of sinew surface, rather than when you stretch it only 1.5%. In sinew-wood-horn composites, the added weight of the dense sinew-glue matrix is traded against the ultimate performance sinew can give, but also requiring more than most woods can take in compression, hence the horn belly.
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You're getting a bit carried away with untested knowledge here...... Make all the bows and THEN come back with the " how and why".
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joachim
I have been intrigued by the use of fiber backings and flax is often cited to have good potential. My research has shown that some of the best flax in the world comes from your country, and it seems that flax harvested for other uses may not be as strong as it could be, or the best that bowyers would like have for their use. Certainly the strongest flax would be of interest for string making too.
Have you looked into how to make best use of your local flax, built with/or used flax in your bows or sourced some local flax that might might have been harvested and retted for optimal strength? Perhaps the bowyers in this community would find reports of this type more pertinent than speculations about sinew or some cheap mexican twine salvaged for use in your last bow project.
Just sayin, as there are guys here that would like to get their hands on the best flax in the world if there was a way,
willie
I'm in the process of tillering a flax-backed bow, but I'm going slowly. We do have absolutely superb flax, grown even locally. here's a sample with nice looong fibres that will back at least four to five bows. Once you have your hide glue, you back an entire bow in 20 minutes.
This flax is still commonly used by plumbers to seal pipe fittings, so you find this in hardware stores for 5€ per bundle shown. You could get entire bales of this stuff http://www.albertbrille.be/products%20English.htm
If you want to try a sample, I could probably send you such a bundle overseas.
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when you back a bow with sinew,, you do not have to put a lot to gain poundage,,using a minimum amount to hold the reflex desired is optimum,, I just made sinew bow with 600 to 700 grains of sinew on the back,,it is holding 4 inches of reflex,, the layer of sinew is very thin,,I am sure the plant fiber backs have advantages,, I dont know about them,, but am open to learning,, I like sinew,, but am still a beginner and learning every bow I make,, I just like making bows and improving if I can,, :)
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How many Paleo peoples backed bows with Flax Vs. Sinew? That may answer the questions you are asking. If it was done, why did it stop, and if it wasn't, why wasn't it?
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Joachim
the offer is appreciated, and if the flax I have proves unsatisfactory I will take you up on that. Almost all flax grown in the Americas is grown for seed, consequently the fiber salvaged after seed harvest is said to be premature and brittle. Fiber purchased from the yarn spinning shops is rated by its users for its ease of use or appearance, but little can be found out about it's production specs, as it comes from suppliers that do not pass the info along to the retailers. Do you know of flax grown, harvested and processed for its strength qualities?
As flax is not native to the Americas, I am as interested as JoJo if you know of any examples of primitive fiber bow backings from European cultures?
willie
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Flax is gaining momentum as a biocomposite material for a wide range of uses. You can even buy unidirectional flax "tape". I'll try to find link that shows this without being an Ad.
http://www.jeccomposites.com/news/composites-news/analysis-tensile-behaviour-unidirectional-flaxepoxy-plies