How much can a sinew backed bow be reflexed without being supported by horn on the belly?

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How much can a sinew backed bow be reflexed without being supported by horn on the belly?

dvarela934
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March 7th, 2018, 1:43 am #1

I’m curious how far a bow can be reflexed and still achieve a 20 plus inch draw with no horn? And when do you reach the point of diminishing returns as far as the amount of sinew ?


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Tim Baker
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March 11th, 2018, 1:11 am #2

dvarela934 wrote: I’m curious how far a bow can be reflexed and still achieve a 20 plus inch draw with no horn? And when do you reach the point of diminishing returns as far as the amount of sinew ?


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Dvarela:

That depends on a lot of things:
How long is the bow?
What wood?
What's its intended draw length?
How wide at the fades and at mid limb?
Estimated drawweight at 20-nches before adding sinew?
Will the bow be pulled and held in reflex while the sinew is applied and cures? Recommended.
 
Without this information, a quick and dirty answer is:
Secure the bow into 4" of reflex when applying the sinew. To prevent the sinew lifting as it shrinks and tries to become straight, pull the bow into a bit more reflex each day till the sinew is hard dry.
Apply layers of sinew totaling about half of limb thickness, which will dry to about half that thickness.

Tim Baker
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dvarela934
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March 11th, 2018, 1:38 am #3

Tim Baker wrote:
dvarela934 wrote: I’m curious how far a bow can be reflexed and still achieve a 20 plus inch draw with no horn? And when do you reach the point of diminishing returns as far as the amount of sinew ?


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Dvarela:

That depends on a lot of things:
How long is the bow?
What wood?
What's its intended draw length?
How wide at the fades and at mid limb?
Estimated drawweight at 20-nches before adding sinew?
Will the bow be pulled and held in reflex while the sinew is applied and cures? Recommended.
 
Without this information, a quick and dirty answer is:
Secure the bow into 4" of reflex when applying the sinew. To prevent the sinew lifting as it shrinks and tries to become straight, pull the bow into a bit more reflex each day till the sinew is hard dry.
Apply layers of sinew totaling about half of limb thickness, which will dry to about half that thickness.

Tim Baker
Thanks Tim that’s helpful. I have heard that sinew can be 25% of the limb thickness but wasn’t sure whether that was before or after drying. Important discrepancy.

I just added a third layer of sinew to this bow

It may be getting close to 25 percent but I should have thinned the limbs before applying to get more reflex. The bow is now 60 pounds at 24 inches. It’s hickory. 50 inches. The reflex unstrung looks like this




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dvarela934
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March 11th, 2018, 3:22 am #4

In your opinion what the most efficient bow design using wood and sinew. Namely what type of wood what length draw weight thickness recurve etc. ?


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dvarela934
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April 1st, 2018, 1:15 pm #5



2nd layer on cherry bow


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Tim Baker
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April 4th, 2018, 12:10 am #6

Likely the best combination is sinew over juniper, tillered and held into several inches of reflex while sinewed. Sinew over yew might be next. Highly elastic in compression woods are best with sinew.

I just sinewed bamboo, pulled into 5" of reflex. As an experiment it wasI first "sinewed' with half the bamboo's thickness of cotton string--as a means of elevating the sinew so it would do more work. Then applied almost that thickness again of sinew over the cotton [thickness measured dry. The bow is almost twice as thick as the bamboo. It's now drawing nearly four time the weight of the bamboo alone, and holding 6" of just-unbraced reflex. It's only been taken to half draw, waiting for the sinew to fully dry. Should be an exceptionally fast bow. It's essentially a 'D' bow, but highly reflexed, with especially narrow outer limbs and tips
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dvarela934
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April 4th, 2018, 12:17 am #7

Interesting idea about the cotton. I have neve we heard of that. You see my cherry bow with 2 layers and I’m likely going to put a third. I’m trying to get to 25%. Oh the thickness. Will more than 25% sinew make it slow and heavy even if it may induce heavy reflex???


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dvarela934
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April 4th, 2018, 1:34 am #8

Tim Baker wrote:Likely the best combination is sinew over juniper, tillered and held into several inches of reflex while sinewed. Sinew over yew might be next. Highly elastic in compression woods are best with sinew.

I just sinewed bamboo, pulled into 5" of reflex. As an experiment it wasI first "sinewed' with half the bamboo's thickness of cotton string--as a means of elevating the sinew so it would do more work. Then applied almost that thickness again of sinew over the cotton [thickness measured dry. The bow is almost twice as thick as the bamboo. It's now drawing nearly four time the weight of the bamboo alone, and holding 6" of just-unbraced reflex. It's only been taken to half draw, waiting for the sinew to fully dry. Should be an exceptionally fast bow. It's essentially a 'D' bow, but highly reflexed, with especially narrow outer limbs and tips
Also do you have any pictures of this cotton bow. ?? Seems like a cool design.


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Tim Baker
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April 4th, 2018, 7:27 am #9

Very roughly speaking, if you double the thickness of the bow by adding sinew you'll increase the draw weight by four times. If doubled by using wood it would be 8 times stiffer, but sinew is much less stiff in tension than wood.
 
If you add sinew that is 60% thicker than the wood the bow's draw weight will roughly double.
 
If  25% thicker the draw weigh will rise somewhere around 20%, a 50lb bow becoming about 60lb.
 
Sinew is roughly twice the mass of wood, so a same-poundage bow of wood weighing 24 ounces will weigh almost 30 ounces. But with a large reflex, and keeping sinew mass largely away from the outer limbs, speed will be noticeably faster than an unsinewed flat or lower-reflexed version. 
 
Before sinewing it's best to tiller the bow to a bit less than half draw, assuring that it can be pulled into large reflex without over-straining the wood.
 
To save mass where it hurts performance most, feather the sinew out to zero several inches before reaching the nocks.
 
I'd post a photo of the double-thickness bamboo/cotton/sinew bow, but can't figure out how to.
 
Tim Baker
 
 
 
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Michael Bootz
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April 4th, 2018, 10:43 am #10

Tim Baker wrote: I'd post a photo of the double-thickness bamboo/cotton/sinew bow, but can't figure out how to.
Easy:
  • Click on the "Add files" button on the lower right:
    PhotoPosting01.jpg
  • In the file selector that opens, navigate to and select the photo on your computer, then click "open":
    PhotoPosting02.jpg
    Now your photo is uploaded and should appear below the post editor window.
  • In the post editor, move the cursor to the place in your post where you want the photo to appear, then press the "Place inline" button:
    PhotoPosting03.jpg Note that if you upload multiple photos in one post then there will be a separate entry for each photo. Make sure you press "Place inline" for the correct photo.
  • Now the photo should appear in your post:
PhotoPosting04.jpg
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Tim Baker
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April 5th, 2018, 12:12 am #11

Bamboo belly, cotton string in glue core, sinew. 

DSC01126. 18 jpg - Copy (2).jpg
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dvarela934
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April 5th, 2018, 10:14 pm #12

Tim Baker wrote:Bamboo belly, cotton string in glue core, sinew. 

DSC01126. 18 jpg - Copy (2).jpg
Wow!


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dvarela934
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April 6th, 2018, 10:28 am #13



4th layer. Mainly in the handle area


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Tim Baker
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April 6th, 2018, 5:29 pm #14

Looking forward to the results.  
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dvarela934
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April 7th, 2018, 1:13 pm #15


Too thick ?


I’m noticing an issue now. At the onset I tried to steam reflex the tips. It was not very successful but 1 tip. The left in the above photo got a crack and I’m afraid I’ll have to stop reflecting it because it’s bending the tip too much if that makes sense


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Tim Baker
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April 8th, 2018, 3:18 am #16

Cherry is harder to steam bend to small diameter curves than most bow woods, tolerating less than half the curve diameter of red oak, for example. That's possibly the problem. It it's present position is ok, but there's a chance the curve might flatten when drawn, you could reinforce it with more sinew, or on the belly side with a layer or two of veneer.  If for some reason you bail on this bow you can soak it for a day or so then remover the sinew and wash it free of glue and use it again. 
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dvarela934
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May 17th, 2018, 2:19 am #17

Tim Baker wrote:Cherry is harder to steam bend to small diameter curves than most bow woods, tolerating less than half the curve diameter of red oak, for example. That's possibly the problem. It it's present position is ok, but there's a chance the curve might flatten when drawn, you could reinforce it with more sinew, or on the belly side with a layer or two of veneer.  If for some reason you bail on this bow you can soak it for a day or so then remover the sinew and wash it free of glue and use it again. 



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dvarela934
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May 17th, 2018, 2:21 am #18

dvarela934 wrote:
Tim Baker wrote:Cherry is harder to steam bend to small diameter curves than most bow woods, tolerating less than half the curve diameter of red oak, for example. That's possibly the problem. It it's present position is ok, but there's a chance the curve might flatten when drawn, you could reinforce it with more sinew, or on the belly side with a layer or two of veneer.  If for some reason you bail on this bow you can soak it for a day or so then remover the sinew and wash it free of glue and use it again. 



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dvarela934
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May 17th, 2018, 2:23 am #19

An update


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Beadman
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May 19th, 2018, 3:08 pm #20

dvarela934.....Unfortunately black cherry is one of those woods I found that does'nt like extreme reflexed designs.Especially on shorter bows.It's the problem of it's belly chrysalling.Only drawing it to 20" might relieve that though.To a longer draw of say 28" it can get sketchy with black cherry.It is understandable though trying cherry.It is a very sweet smooth pulling type wood for sure.Reason why longer even bendy handled bows of black cherry on their own are very nice to shoot.
To answer your initial first question Tim's requried info needed is valid too.What I've found just using tough old hickory with a heat treated belly is that it can be reflexed with to a good 10" without horn if so desired.That's on a bow 62" or longer though and still drawn to 28".
They are good sharpen up a person's tillering skills.Any wood has it's limits of compression.Some more so than others.
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