Author Topic: Increasing stored energy in laminated bows.  (Read 3767 times)

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Offline Springbuck

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Re: Increasing stored energy in laminated bows.
« Reply #15 on: January 04, 2017, 06:46:51 pm »
I don't know exactly about the answer to the original question, but let me share an experiment I did once.

I wanted to make a slightly deflexed bow with parallel limbs for most of the length, and super tiny, skinny, pretty sharply angled tips, like molly tips, but with about a 60° angle and 10" long or so.   No, I don't remember why I wanted to do something this odd, but it was early on and I was learning. I know I was interested in figuring out limits back then.  I still have the bow. 

 So, I backed some QS black locust with hickory, bent the tips in both, and glued up.  The tips ended up really skinny, less than 3/8 wide the whole 10" of length, and maybe 1/4"  at the nocks.  Also, only about 1/4" front to back at the tip, and maybe 1/2" thick where they kinked at the recurves. 

ANYWAY, they bent sideways like tall grass in a high wind.  So, trying to save the bow, I actually sanded the tips down even more, side to side, like 1/4" side to side, maybe less.  I left the very tips alone.  Then, for each tip, I made two 8" long stays out of bamboo garden stakes. I ground these 1/16" thick-ish. 

Here is the cool part!!!    I took these little bamboo slats and bent them over rind down, on a form I had made for R/D limbs, and cooked them in place with a torch.  I torched the pith side.   Then I went back and applied them to the SIDES of the skinny limb-tip with TB III.

See, I cooked them into a curve, then Perry DEFLEXed them in place, really just to straight.  I was hoping that by adding the curve first, then gluing/clamping them flat,  the slats would be pre-stressed enough to really stiffen the limb tip laterally.  It WORKED!  The limb tips were about the same width as before, but WAY stiffer side to side.  Get it??  Lateral Perry reflex.

Sorry so long winded with no pics, but I have since wondered if the same technique could be used to raise stability and lateral stiffness in a limb.  Say, for instance I wanted to do a bamboo-backed R/D with some belly wood or other. What if I ripped the belly lam in half lengthwise, right down the midline.  Then imagine if I used various clamps to curve each half away from the other and heat treated it in place (or even did multiple laminations laterally like a side to side Perry reflex, meeting in the middle.)  When I pull them back together side to side, then force reflex them into the R/D form, I'm wondering what that would do as far as both lateral and torsional stability of the limb? 

I do know the same trick works on arrows.  I made some high spine, skinny arrows using the same trick.

Anyway.  I'll put it on the list.
« Last Edit: January 04, 2017, 07:10:42 pm by Springbuck »

Offline Pappy

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Re: Increasing stored energy in laminated bows.
« Reply #16 on: January 05, 2017, 08:41:47 am »
No idea on the question ??? but good to see you back on Doc. ;) :)
 Pappy
Clarksville,Tennessee
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Offline RyanY

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Re: Increasing stored energy in laminated bows.
« Reply #17 on: January 05, 2017, 10:09:00 am »
That makes sense but I think there definitely needs to be a control for just using straight slats without that pre bend. It would be cool to do some bend tests to see if energy storage changes with pre stressed limbs. I also wonder if increasing glue surface area effects energy storage like the grooves used in horn bows.

Pappy, good to be back! In the easier part of my last year of school. I got started on a bow yesterday!  ;D

Offline willie

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Re: Increasing stored energy in laminated bows.
« Reply #18 on: January 05, 2017, 03:17:07 pm »
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I do know the same trick works on arrows.  I made some high spine, skinny arrows using the same trick.

interesting experiment and results, Springbuck.  just to be sure I understand your layup, did it look like   )|(   ?, before you clamped and glued? I don't know how often one might have reason to stiffen siyahs, but the technique seems to be worth exploring further, especially for laminated bamboo arrows. Perhaps you can write more about your arrows?

there was a good discussion recently about split bamboo arrows here...

http://www.primitivearcher.com/smf/index.php/topic,56266.0.html


Quote
It would be cool to do some bend tests

Ryan,
  I agree, especially seeing how there are various explanations, or at least some doubts about some of the explanations of the "Perry" effect.
 
  It just so happens that  am in the process of gluing some samples up, for testing of a backing, in a somewhat controlled test of my own.  Could you suggest a test? If it is within my capabilities, I would be willing to make up a few additional samples.
« Last Edit: January 05, 2017, 03:44:38 pm by willie »

Offline PatM

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Re: Increasing stored energy in laminated bows.
« Reply #19 on: January 05, 2017, 03:53:36 pm »
I don't know how often one might have reason to stiffen siyahs.

  The presence of bone slats in ancient composites show the importance they placed on stiffening siyahs laterally.

Offline Badger

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Re: Increasing stored energy in laminated bows.
« Reply #20 on: January 05, 2017, 06:46:08 pm »
I don't think looking at it in terms of stored energy would really apply. Possibly stiffness per mass ratio might be a good way to evaluate it. The stored energy is more a product of geometry. All springs have one thing in common, they build at so much per inch. So regardless of how stiff it is it is still basicaly a work in work out measurement.
I do notice that bows with a laminated back tend to be a little thinner than self bows. I also believe they get strained less when pulling them out of reflex into brace. They tend to be slightly more efficient.

Offline Springbuck

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Re: Increasing stored energy in laminated bows.
« Reply #21 on: January 05, 2017, 09:42:12 pm »
Quote
  just to be sure I understand your layup, did it look like   )|(   ?, before you clamped and glued? I don't know how often one might have reason to stiffen siyahs, but the technique seems to be worth exploring further

Yes, just like that.

 Thanks for reading the whole thing!   :-)


Offline Springbuck

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Re: Increasing stored energy in laminated bows.
« Reply #22 on: January 05, 2017, 09:45:11 pm »
 The presence of bone slats in ancient composites show the importance they placed on stiffening siyahs laterally.
[/quote]

  What interests me really is making them lighter, longer, skinnier, for the same stiffness.

Offline PatM

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Re: Increasing stored energy in laminated bows.
« Reply #23 on: January 05, 2017, 09:47:53 pm »
The presence of bone slats in ancient composites show the importance they placed on stiffening siyahs laterally.

  What interests me really is making them lighter, longer, skinnier, for the same stiffness.
[/quote]

 That was likely their intention. Keeping in mind that their bows were very heavy in draw weight relative to the weight of the tips.

Offline Springbuck

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Re: Increasing stored energy in laminated bows.
« Reply #24 on: January 05, 2017, 09:55:01 pm »
I don't think looking at it in terms of stored energy would really apply. Possibly stiffness per mass ratio might be a good way to evaluate it. The stored energy is more a product of geometry.
do notice that bows with a laminated back tend to be a little thinner than self bows.
Quote

Yeah, this is the crux.   "Stiffness per mass ratio" also pre-supposes that the lower mass can survive the geometry that stores the energy.

  Sometimes, these bows actually end up physically more massive, but only a bit, while allowing geometry that stores much more energy.  It seems so, anyway.

Offline willie

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Re: Increasing stored energy in laminated bows.
« Reply #25 on: January 06, 2017, 03:17:48 am »
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I do notice that bows with a laminated back tend to be a little thinner than self bows.............. get strained less


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Sometimes, these bows actually end up physically more massive


Astute observations, guys.   Good food for thought