Perry reflex

[Allyn T]

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

[mmattockx]

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

[Allyn T]

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

[PatM]

  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.

[Selfbowman]

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

[Badger]

    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.

[Badger]

    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.

[DC]

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.

[mmattockx]

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

[Allyn T]

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

[mmattockx]

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

[DC]

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?

[Allyn T]

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

[willie]

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.

[DC]

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