Sinew question

[willie]

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.

[bradsmith2010]

Hmmmmm

[BowEd]

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.

[gfugal]

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.

[bjrogg]

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

[Tom Dulaney]

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.

[bradsmith2010]

I dont think reflexing is stressing unnecessarily ,, it can add cast to the bow,, a chrono will varify that on two like bows,,

[bradsmith2010]

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,,

[Stick Bender]

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.

[Tom Dulaney]

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. 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.

[willie]

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

[Tom Dulaney]

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.

[gfugal]

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. 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.

[Stick Bender]

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.

[PatM]

gfugal, you believe sinew backing is a stiff material?