Why use sinew when you have plant fibers

[PEARL DRUMS]

Joachim have you ever built a sinew backed bow?

[bubby]

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

[joachimM]

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
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

[JoJoDapyro]

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?"

[Jax666]

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

[joachimM]

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

[willie]

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

[joachimM]

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?

[willie]

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

[vinemaplebows]

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?

[joachimM]

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.   

[PatM]

 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. 

[joachimM]

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

[joachimM]

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.

[PatM]

" Crude estimations" have no place in proving a point.