Experimenting with sinew.

Tim Baker
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9:35 AM - Apr 12, 2018 #1

Sinew is useful for keeping short bows from breaking, but is not good at increasing the cast of mid-length and longer wooden bows. This is largely because sinew is lightly strained in such situations, and has high mass.

The idea here is to cause the sinew to be far more strained than typically, making it do far more work per mass. Elevating the sinew well above the bow back would would accomplish this by  increasing it's percentage of stretch.

This first experiment elevated the sinew by placing a filler of hide glue-soaked cotton string between the back and the sinew.

The belly is bamboo, 46" long, weighing 5.5 ounces.
The dry weight of the sinew and glue is about 2 ounces.
Once in place the bow was twice as thick as the bamboo alone.
The bow was held in 5" of reflex when sinewed, holding 6" of just-unbraced reflex.
Draw weight rose 400% of that of the bamboo alone!
Some touch-up tillering is needed, so corrective amounts of sinew will be added in a couple of areas before going to full draw, and a visit to the chronograph. My guess it that it will well outshoot same-draw weight conventionally sinewed wooden bows, and Asiatic composites. We'll see.

Meanwhile, please let me know of other efforts to get more work out of sinew by elevating it above the bow back.  And your results, and details, if you do something along these lines yourself.

Arguments, comments and suggestions welcomed.

Tim Baker
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Fundin
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12:51 PM - Apr 12, 2018 #2

Cool, with a recent fourth baby I have little time for experiments, but there are some ideas along thees lines I would like to explore. A balsa beam along the center of the bow could probably do a lot if sinew backed.
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Tim Baker
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8:08 PM - Apr 12, 2018 #3

Fundin:

Yes, the cotton string-glue elevator wasn't the best route. It's not as heavy as sinew, but is as heavy as bow wood itself. Mainly what it did iwas save about half of the sinew otherwise needed. The plan was to next use redwood but your balsa idea might be better. Will have to see it if will hold up to the compressive forces involved. Still, this first experiment was valuable: doubling bow thickness with a high % of elevated sinew increased draw weight, therefore energy storage by 400% while increasing bow mass by less than half.
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sleek
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5:50 AM - Apr 13, 2018 #4

Tim Baker wrote: Fundin:

Yes, the cotton string-glue elevator wasn't the best route. It's not as heavy as sinew, but is as heavy as bow wood itself. Mainly what it did iwas save about half of the sinew otherwise needed. The plan was to next use redwood but your balsa idea might be better. Will have to see it if will hold up to the compressive forces involved. Still, this first experiment was valuable: doubling bow thickness with a high % of elevated sinew increased draw weight, therefore energy storage by 400% while increasing bow mass by less than half.
Tim, it seems like a series of string bridges across the back would elevate the sinew, but that just becomes a cable backed bow. Whats the difference between what a cable bow can offer and what you are trying here?
Once I was making some paleo mulch from a stick and after many hours was astonished to find myself holding a bow.
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Fundin
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7:30 AM - Apr 13, 2018 #5

 correct thickness of the balsa, sinew and bow should put the balsa around the neutral plane. If the balsa is too weak, spruce, aspen or willow should do it. A Paleo way of attaching it would be to split a sapling and "splice" it at the handle, natural taper, very easy work even with stone tools, and glued as per fenno ugric bows with a fish skin glue of semi solved state (to make it filling so the fit does not have to be perfect fit). (Soon we will have reinvented the sinew backed fenno ugric bow found in the Baltic, possibly Estonia if memory serves me right...)
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sleek
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8:18 AM - Apr 13, 2018 #6

What about cork? It seems better in compression than balsa, ( an opinion only no facts to back that claim ) and it wouldnt soak up hide glue like cotton.
Once I was making some paleo mulch from a stick and after many hours was astonished to find myself holding a bow.
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sleek
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6:52 PM - Apr 13, 2018 #7

I think I will try one of cork. Maybe 1/4 inch thick. I have a short design i like to build that this may work well with.
Once I was making some paleo mulch from a stick and after many hours was astonished to find myself holding a bow.
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Tim Baker
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8:00 PM - Apr 13, 2018 #8

Sleek:  
 
Needs more thought, but elevating the sinew with bridges might not be efficient. Possibly the belly, core and sinew have to be rigidly connected  in order for sheer forces to cause energy to be stored instead of escaping as the layers slide by each other.
 
The sinew on cable bows is not highly elevated and not of large enough diameter to raise draw weight as in this experiment. And possibly the sheer-slippage situation too. 
 
Fundin:  
 
Good thinking. And we're on the same paleo page. A wood core, as on modern wood backings, isn't paleo, so I'll stick with natural fiber and glue or some such. Recently I whipped some hide glue into a foamy froth which dried to about .10 specific gravity and quite rigid. I'll try to make a batch both very light and rigid enough to serve as the sinew elevator here. That would be ideal.
 
Sleek: 
 
Good idea to try cork. It might be stiff enough to resist the mentioned sheer slippage, if that's actually an issue. 
 
Tim
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toxophileken
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10:14 PM - Apr 13, 2018 #9

Great thoughts on this thread.

My two cents:  Balsa and cork probably won't handle the shear strain.  I've been experimenting with juniper as a core wood.  So far, no shear failures, but my tests are by no means exhaustive.

Tim, forgive the tangent here, but on a longer bow, what about making one section of the limb take more strain, and feathering in sinew there?

Ken
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Tim Baker
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10:43 PM - Apr 13, 2018 #10

Ken:

I don't fully understand the question, but maybe this will glancingly answer it: Final versions will be generally as described, but the outer limbs will be narrow, thicker, relatively non-bending and all wood, the core-elevator/sinew feathering into this portion. 

Recently whipped some hide glue into a foamy froth; when it dried it was about .10 specific gravity and quite rigid. Some versions of that might be the ideal elevator. Experiments needed. 

Tim
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toxophileken
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4:18 AM - Apr 14, 2018 #11

Tim, I saw your earlier post about the foamy/thick hide glue.  My concerns re shear strength would be similar in that instance as in the cork (which is bark) or super light woods.

I was asking about doing exactly what you are doing already - selective additive tillering by placing sinew in specific areas.  Let's consider a limb where we concentrate the bend.  That is the location that needs extra tension help.  If severe enough, it also needs compressive help, and then you end up with a horn bow.  My thought was, on a longer bow, where sinew wouldn't be strained enough to pay for its mass, maybe make the bend of the limb more isolated, and back that section with sinew.  Sorry for the tangent.

Nice talking to you, by the way!

Ken
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Tim Baker
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7:08 AM - Apr 29, 2018 #12

Here's a piece of the mentioned hide glue foam:
DSC01300. 10 jpg.jpg
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Tim Baker
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5:28 PM - Apr 29, 2018 #13

Ken:
 
Yes, shear strength is the concern. Only tests will tell for certain of course. I'm optimistic that this version or another will do the job and at strikingly low specific gravity. I'll mail you the pictured sample so you can get the same visceral sense of it that I have. It's amazingly tough and stiff stuff. I'm puzzled why it hasn't been put to some use before now. Figuring a predictable way to generate volume and consistency of it will take some doing though.
 
Tim
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Abe
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11:49 PM - May 01, 2018 #14

Tim Baker wrote:Sinew is useful for keeping short bows from breaking, but is not good at increasing the cast of mid-length and longer wooden bows. This is largely because sinew is lightly strained in such situations, and has high mass.

The idea here is to cause the sinew to be far more strained than typically, making it do far more work per mass. Elevating the sinew well above the bow back would would accomplish this by  increasing it's percentage of stretch.

This first experiment elevated the sinew by placing a filler of hide glue-soaked cotton string between the back and the sinew.

The belly is bamboo, 46" long, weighing 5.5 ounces.
The dry weight of the sinew and glue is about 2 ounces.
Once in place the bow was twice as thick as the bamboo alone.
The bow was held in 5" of reflex when sinewed, holding 6" of just-unbraced reflex.
Draw weight rose 400% of that of the bamboo alone!
Some touch-up tillering is needed, so corrective amounts of sinew will be added in a couple of areas before going to full draw, and a visit to the chronograph. My guess it that it will well outshoot same-draw weight conventionally sinewed wooden bows, and Asiatic composites. We'll see.

Meanwhile, please let me know of other efforts to get more work out of sinew by elevating it above the bow back.  And your results, and details, if you do something along these lines yourself.

Arguments, comments and suggestions welcomed.

Tim Baker
I’m relatively new to this but if I’m following the principal being the bridge between the sinew backing and the bow consisting of a natural material, with as little mass as possible, and able to perform under the energies it is exposed to on the neutral plane of the bow, I’m curious if notochord from a sturgeon or a shark would be something that is viable. Just a thought. I am going to try experimenting with this very soon. Thank you for the input and results so far. 400% is unreal. Really. Well..you know what I mean.

If that style bow could outshoot the Asiatic composite bows that would be history making would it not?


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Tim Baker
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1:38 AM - May 02, 2018 #15

Abe:
 
So far I haven't found the mechanical properties of notochord. If like cartilage it would be too compressible. We'll see.
 
Some thoughts on this elevated sinew design:
Double the thickness of a 5-pound bow and draw weight goes up 800% to 40lbs.
This test bow rose from 5.5lbs to about 24lbs, almost 400%
But less than doubling it's thckness would equal that 400%, so why bother with elevating sinew, why not just make the bow a little thicker to begin with?
 
When at 5.5lbs the limb is thin enough for bending into extreme reflex without over straining the wood, allowing high early draw weight for a fat F/D curve and high energy storage.
Sinew can safely stretch up to 8% of length compared to wood's 1%. Elevating it a given height above the belly will cause it to stretch far and hard enough to raise drawweigh by several times. But the elevator, or spacer must be stiff enough to not allow surrender of any of the sinew's stretch, yet be elastic enough for extreme stretching of itself as the bow is braced and drawn. Much pondering ahead. 
 
" If that style bow could outshoot the Asiatic composite bows that would be history making would it not?"
 
Well designed and tillered self wood straight bows often presently outshoot typical Asiatic composites, all shooting 10-grain per pound arrows. Due to their high dry-fire speed, well made Asiatic composites outshoot well made straight wood bow if shooting light arrows. This test bow type would have the advantage of lighter limbs, especially far lighter outer limbs, aiding dry-fire speed.
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ww
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1:47 AM - May 02, 2018 #16

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Abe
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7:35 AM - May 05, 2018 #17

Tim Baker wrote:Abe:
 
So far I haven't found the mechanical properties of notochord. If like cartilage it would be too compressible. We'll see.
 
Some thoughts on this elevated sinew design:
Double the thickness of a 5-pound bow and draw weight goes up 800% to 40lbs.
This test bow rose from 5.5lbs to about 24lbs, almost 400%
But less than doubling it's thckness would equal that 400%, so why bother with elevating sinew, why not just make the bow a little thicker to begin with?
 
When at 5.5lbs the limb is thin enough for bending into extreme reflex without over straining the wood, allowing high early draw weight for a fat F/D curve and high energy storage.
Sinew can safely stretch up to 8% of length compared to wood's 1%. Elevating it a given height above the belly will cause it to stretch far and hard enough to raise drawweigh by several times. But the elevator, or spacer must be stiff enough to not allow surrender of any of the sinew's stretch, yet be elastic enough for extreme stretching of itself as the bow is braced and drawn. Much pondering ahead. 
 
" If that style bow could outshoot the Asiatic composite bows that would be history making would it not?"
 
Well designed and tillered self wood straight bows often presently outshoot typical Asiatic composites, all shooting 10-grain per pound arrows. Due to their high dry-fire speed, well made Asiatic composites outshoot well made straight wood bow if shooting light arrows. This test bow type would have the advantage of lighter limbs, especially far lighter outer limbs, aiding dry-fire speed.
Tim: “So far I haven't found the mechanical properties of notochord. If like cartilage it would be too compressible. We'll see.”

While living in Pendleton Oregon in the mid 90’s I met a some hippy looking dude one day out on the local archery range and he was shooting a recurve. It was a really nice take-down. I had never seen one and I was immediately drawn to the small package for backpacking, the functionality. He asked what I was shooting and I handed him a rawhide backed 57# Yew longbow my Dad had made which at that time I had shot 1000’s of times. The back was hammered. Weather-checked and fuzzy on the edges. The belly was all scratched up..dents all over the place...it had Purple Heart tip overlays...and teeth marks from one of my pit-bull puppies..beaver fur silencers...I loved that bow. I was proud.
He was looking it over pretty good. He was glued to it. Turns out he was some anthropologist that was studying the tribes in the area and he told me then that some of the Indians along the Columbia River made their bows from chokecherry and their arrows from wild rose. When I asked about glue he said they chewed up dry sturgeon bladder and spit it out mixed with saliva. Some bow strings were made from the “neural chord” of a Sturgeon. I have no idea what process they would have used but I’ve been curious to know what the mechanical properties would be since then. If they made strings maybe it would give too much. Baleen perhaps..it’s long enough. Easy enough to acquire. Pretty tenacious stuff.


“Some thoughts on this elevated sinew design:
Double the thickness of a 5-pound bow and draw weight goes up 800% to 40lbs.
This test bow rose from 5.5lbs to about 24lbs, almost 400%
But less than doubling it's thckness would equal that 400%, so why bother with elevating sinew, why not just make the bow a little thicker to begin with?”


If sinew added would result in less overall mass than the added bowwood to achieve that 400% and keep the bamboo from taking a set than it would seem to be a 2 for 1.


“But the elevator, or spacer must be stiff enough to not allow surrender of any of the sinew's stretch, yet be elastic enough for extreme stretching of itself as the bow is braced and drawn. Much pondering ahead.”

Baleen could do it I bet.

“Well designed and tillered self wood straight bows often presently outshoot typical Asiatic composites, all shooting 10-grain per pound arrows. Due to their high dry-fire speed, well made Asiatic composites outshoot well made straight wood bow if shooting light arrows.”

I had no idea although I should have known given the irons in the fire. And I hate to sound ignorant but is dry-fire speed referring to the reaction of the limbs without the arrows resistance when the string is released from full draw? Is that doable? More than once? Like I said..hate sounding stupid. But I’m not hip to that term.





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Tim Baker
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8:28 AM - May 05, 2018 #18

Abe:
 
There's a stash of baleen here so I'll play with it.
 
"  ...is dry-fire speed referring to the reaction of the limbs without the arrows resistance when the string is released from full draw? Is that doable? More than once? 
 
Yes, dry-fire mean releasing the bow from full draw without an arrow, and yes, you're correct to be suspicious of the wisdom of such. But you don't have to actually dry fire a bow to get a good sense of  what that speed would be. Instead you can chart the speed of the bow as it shoots a series of ever lighter arrows and see where the graph line projects for a zero-mass arrow. 
 
Short bows have higher dry-fire speeds because they don't have to haul long, heavy limbs forward. Long bows are way inefficient if shooting light flight arrows, but become more and more efficient with heavier arrows, all of the bow's energy put into accelerating the heavy acceleration-resisting arrow. 
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Abe
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4:03 PM - May 05, 2018 #19

Tim Baker wrote:Abe:
 
There's a stash of baleen here so I'll play with it.
 
"  ...is dry-fire speed referring to the reaction of the limbs without the arrows resistance when the string is released from full draw? Is that doable? More than once? 
 
Yes, dry-fire mean releasing the bow from full draw without an arrow, and yes, you're correct to be suspicious of the wisdom of such. But you don't have to actually dry fire a bow to get a good sense of  what that speed would be. Instead you can chart the speed of the bow as it shoots a series of ever lighter arrows and see where the graph line projects for a zero-mass arrow. 
 
Short bows have higher dry-fire speeds because they don't have to haul long, heavy limbs forward. Long bows are way inefficient if shooting light flight arrows, but become more and more efficient with heavier arrows, all of the bow's energy put into accelerating the heavy acceleration-resisting arrow. 
Tim: Thank you for explaining the dry-fire graph line. That makes perfect sense.



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sleek
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4:16 PM - May 05, 2018 #20

Tim, what if you were to use that coconut fiber matrix used as planters matetial?
Once I was making some paleo mulch from a stick and after many hours was astonished to find myself holding a bow.
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