Primitive Archer
Main Discussion Area => Bows => Topic started by: Allyn T on November 04, 2020, 07:58:45 pm
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Ok let's get into it, the benefit of perry reflex is caused by surface travel and opposing forces, that's a generalized statement to get us started, here are my questions.
1. Using a wood slat(not bamboo) if you deflexed both slats using heat then perry reflexed them would it have the effect of extra reflex at a less reflexed resting state?
2. If you had a naturally deflexed stave(someone recently posted a deflexed yew) would perry reflexing to say a flat position be a good way to make that a great preformer?
3. If you took a deflexed belly lam and a reflexed back lam and glued them together flat, would there be any benefit? I feel like they would be opposing each other still, and the back would have extra tension while the belly being deflexed before glue up would have less strain in compression.
All thoughts are appreciated
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1) I'm not sure what you mean by deflexing both slats? I not sure I see a point to deflexing the backing before pulling it forward, but deflexing the belly lam(s) before pulling them forward to glue the back on makes perfect sense to me. Also consider that heating the backing into deflex may make it brittle and more likely to fail under the tension loads it will see.
I just finished making a thickness sander and plan to do my first lam bow in similar fashion, putting ~6" of deflex into the belly lam glue up (2 lams, one belly, one core), then pulling it forward into ~1.5" of reflex to glue the back on. The goal is a bunch of tension preload on the belly to minimize set but not so much retained reflex that it becomes hard to string, tricky to tiller or overloads the back at full draw.
2) Can't say, but it would lower maximum stresses on the belly the same as I describe above.
3) This should be the same as 'conventional' Perry reflex in terms of reducing the maximum stresses on the belly.
Mark
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Well for 1 I ment deflex both lams(my mistake) and the purpose of deflexing the back would be to place it into compression at a resting state when you reflex them together, the whole point of perry reflex is that the back and belly are fighting to return to their preglued state.
As far as 3 goes it wouldn't be perry reflex exactly but I was wondering if it would still work in that fashion.
The sander setup sounds good it'll be exciting to see how your experiments turn out
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In real life the manipulation of all kinds of lams makes so little difference that it's barely worth speculating on.
I do get that people become intrigued by possibilities but it does cause paralysis by analysis. You may not have time to do much bowbuilding but when you do have time such complex plans will prevent it from ever happening.
People get stalled by overthinking a simple sapling D bow these days.
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Not me Pat. I see a new challenge I just get started. Make some mistakes?Sure. Back to the drawing board so to speak . Arvin
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I think those are all excellent questions you are asking and a good example of continuing research. Most of us will have a run that last 5 or 6 years where we do a lot of experimenting and then just kind of settle in with the occasional experiment following a brains storm. I think what you are talking about is a good place to advance on what we allready know. Hopefully you will keep good records, I regret not keeping any records on anything.
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It got me thinking, if I were going to run some experiments on that I think I would only tiller the bows out to 24" and then later after testing go ahead and tiller them out to 28" and test again. Obviously make them all the same length and as much alike as possible. I think about 10 bows could be a real nice case study.
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If you look back at the technical threads over the last 10 years or so you'll notice one thing. They all just kind of fizzle out and nothing really comes from them. Everyone has their own ideas, some good and some rather hair brained but the problem is that there isn't an easy way to prove this stuff. The physics is apparently extremely complex and no one is willing to spend the time and money to test it. Flight archery is the only branch of the sport that really pushes the limits and it's all backyard bowyers, no reason for a business(money) to get involved so no in depth testing. The money is in target and hunting and you don't need high performance for them. We need a sugar daddy. ;D
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As far as 3 goes it wouldn't be perry reflex exactly but I was wondering if it would still work in that fashion.
I guess that depends on how strictly you define Perry reflex. In my mind they are the same thing in that you are pulling the belly wood into reflex in the glue up to reduce the maximum stresses it sees. #3 wouldn't offer the performance benefits of having the tips reflexed forward in the same way Dan Perry's bows do, but it would offer the same benefits for minimizing set by reducing belly stresses.
The sander setup sounds good it'll be exciting to see how your experiments turn out
I will post as things go along. Finishing the sander was a major hurdle and once I finish the final details my progress should be much more noticeable.
In real life the manipulation of all kinds of lams makes so little difference that it's barely worth speculating on.
Can you explain what you mean with this? Are you talking about combining different woods or the Perry reflex or something else?
I do get that people become intrigued by possibilities but it does cause paralysis by analysis.
This can happen, yes. OTOH, by analyzing many types/designs/sizes of bows on paper/computer I have been able see strengths and weaknesses of many designs without having spent the next 5 years making one of each to test. Engineering analysis is a powerful and valuable tool, but it isn't a magic bullet and you still have to make a bow in the real world in the end.
I have spent most of my bow time this summer building shop infrastructure to let me make lam bows and now that winter has landed I will have more time to work on bows with fewer distractions from the outdoor summer activities.
Mark
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Badger I was really hoping someone else had already done these experiments lol. I would definitely invest the time into it if I could find a sugar daddy like DC suggested! Mark perry reflex isn't just about the belly being in tension it also requires the back to be in compression which if you reflexed the back before hand like in question 3 it would be static reflex instead of trying to fight its way back to neutral. Right now I just have a bunch of hickory staves and a little bit of red cedar and no real good way to try and make a laminate bow, for that matter nor do I have the experience I feel like to do the experiment justice
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Mark perry reflex isn't just about the belly being in tension it also requires the back to be in compression
The back sees almost no compression due to its small thickness relative to the full stack thickness. It sees a tiny bit when bent into reflex, but that is gone almost immediately when the bow is bent towards brace. I haven't figured out how to calculate it yet, but the entire back may be in tension (slightly) even when unbraced because it is holding the thicker belly lam pulled into the reflexed position.
I would be curious to see how much reflex is held off the form with a deflexed back and belly glued together as compared to an undeflexed back. If anyone has tried this please speak up.
Mark
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I'll bring this up again because there's different people here now. If I string a normal bow and stand it on the back porch for a year it's going to take some serious set. Why wouldn't Perry reflexed bows sort of stretch(or shrink) and loose all those internal tensions over time?
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That is a good point DC, though I suppose they would still fight each other just to a lesser degree and moving the bow to brace would still add energy internally
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my guess is that creep would be dependent the stress level, so you might be onto something Don, but not live long enough to see it happen if the stress is not high enough.
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but not live long enough to see it happen
Oh, you don't want to say that to a 73 1/2 year old guy ;D ;D ;D
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my guess is that creep would be dependent the stress level, so you might be onto something Don, but not live long enough to see it happen if the stress is not high enough.
Why would it take so long? You can ruin a bow in a few weeks leaving it braced.
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I feel like if it happened that fast people would have already noticed a pretty quick decline in performance and their perry reflex bows. so either it doesn't happen or there are other forces at work or maybe all the energy comes from moving it to brace and drawing
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The only thing I can relate to it is a raw log. If you let a log cure it can build up stresses that don't release until you split it. Then the two halves go their separate ways. Maybe, as in a braced bow, only the wood that is not constrained can move. Like the belly of the bow is only pushing against air so it can move but inside the bow it's pushing against other wood and so it can't go very far.
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a braced bow is half drawn if you look at how far the tips come back when bent. a gain from perry reflex is quite a bit lesser
a log drying gets the internal stress from drying shrinkage. each cell is shrinking and pulling away from its neighbor
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That kind of makes sense to me but at the same time when set happens it's not just the very outside cells that get crushed it's the ones further in so I feel like the wood could still suffer from set even though it has other wood pushing against it.
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I'll bring this up again because there's different people here now. If I string a normal bow and stand it on the back porch for a year it's going to take some serious set. Why wouldn't Perry reflexed bows sort of stretch(or shrink) and loose all those internal tensions over time?
I expect it is as willie says and the internal stresses are low enough to not suffer from creep to a measurable degree with bows featuring a typical or 'normal' amount of Perry reflex. Maybe someone needs to glue up a test piece with enough reflex to induce the same level of strain as a bow sees at brace and then report back in a few months?
It would be an interesting experiment to try. Maybe I will try it with some scrap wood once I am done my first lam bow if I remember it at that point. The problem is there are so many things to try and only so many available hours to do them in...
Mark
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Ok guys if you build a55# bow and it takes say2-1/2” set will the bow retillered to 45# bow with a better tiller job will it have the same set? Arvin
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in my experience: what you loose does not come back.
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just keep stress to a minumum to prolong life of the bow and yourself,, :)
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So we are crushing cells in the middle of the limb ?
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So we are crushing cells in the middle of the limb ?
not at the very middle, or where the stress is neither tension or compression. It is the worst at the surfaces and progressively less towards the middle.
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Ok guys if you build a55# bow and it takes say2-1/2” set will the bow retillered to 45# bow with a better tiller job will it have the same set? Arvin
I think Badger is the man to answer this question.
So we are crushing cells in the middle of the limb ?
Not into the center of the limb, but that much damage would likely go deep enough that going down to 45# from 55# won't get rid of it. To drop from 55# to 45# only requires a 6.5% limb thickness reduction. If your limb is 0.5" thick, that means you only take 0.0325" off the belly ( for reference 1/32"=0.03125"), which won't be near enough to get rid of the damaged cells.
Badger has commented that when he is tillering a bow using his no set method if he sees a 50# bow start taking set before he is close to his target draw length that he immediately drops it to a 35# target weight and goes from there. I suspect some of that is due to the weight classes in flight, but that gives you an idea of how much drop it takes to lose damaged wood and that is not after 2.5" of set, but as soon as set becomes measurable on the tree.
just keep stress to a minumum to prolong life of the bow and yourself,, :)
Wise words indeed. :D
Mark
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yes if you re tiller, i dont think the set is gonna change much,,
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Thanks Marc I will store that information in my little forgetful head. Arvin
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Ok guys if you build a55# bow and it takes say2-1/2” set will the bow retillered to 45# bow with a better tiller job will it have the same set? Arvin
Sometimes a bow made with Perry reflex will gain reflex as you tiller it. Usually happens in the earlier stages of tillering but in the situation you've described it may gain a little reflex which would hide some of the set. I wouldn't count on it though. Notice that there's a "sometimes" and a "may" in my message. I think they combine exponentially ;D ;D