Primitive Archer
Main Discussion Area => Bows => Topic started by: NTD on December 03, 2010, 01:35:19 am
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Oneeye sent me some laminations for a tril lam bow. I'm thinking about gluing them up this weekend. While pondering what I was going to build I had an idea. I'm sure this theory is nothing new so I'm giving it to you guys to tell me whether it would work, be worth it, etc. Would there be any benefit to gluing the midlam to the core first into deflex and then when I glue on the backing glue in a normal r/d shape? From my limited understanding of how all this works it would allow the bow to store even more energy? Say my final profile I'm looking for 3" relfex tips. If the core and midlam are first deflexed 1" and then once the backing is glued on I pull them into a 3" reflex, then the final reflex would actually be 4", in my pea brain resulting in more energy storage. Is that clear as mud ;) Maybe ??? Thanks for any input.
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Hey Nate.
I'm not sure that I understand what you're saying, but the way my pea brain works, I would think that the deflex would subtract from the reflex. That is, 1 inch of deflex and three inches reflex would net you 2 inches of reflex. Er what?
If you wanted to end up with 3 inches of reflex, with 1 inch of deflex in the handle, you'd have to reflex the tips 4 inches wouldn't you?
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Nate, when I glue up a tri-lam bow I glue the belly to the core first in reflex/deflex then I add the bamboo backing and glue it on with more induced reflex. I think this helps the bow hold its unstrung profile better.
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Thanks for that Ryan.
Cam, by your response I see that I did make it as clear as mud ;D IF you have seen how Marc St. Louis builds his R/D's he glues in defelx at the handle splice. This results in the tips being deflex about 3", at least it did on the one I built. When you apply your backing and pull these limbs to their final reflex shape they have to travel that 3" of deflex to be even plane and then the additional distance for final refelx shape. So if the final profile has 3" of reflex you actually have 6" of reflex...does that make sense? I was just wondering if there would be benefit to applying the same concept in a trilam. Instead of spliced in defelx I start with glued in deflex which would require the limbs to travel further back to get my desired R/D profile...
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120+ views....am I not making sense to anyone ???
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Thanks Scott! What you are saying will happen is exactly what I figured would happen. I just seem to think favoring the belly that way might be a good thing. But I don't know that so figured we could kick it around here.
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You will loose your reflex if you do it that way.
What kind of wood? You can glue the belly and core into high reflex profile then pull some reflex out if you want to protect the back and stress the belly more. You can glue the belly and core with less reflex then add more to increase stress on the backing. It really depends of the wood you are using though. If you are doing Ipe and Boo I wouldn't worry about the back or belly, but if you are using a wood that frets or a backing that will splinter easier, I would change the profile to fit the wood.
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Thanks Justin! It'll be osage belly, bubinga midlam, and bamboo back. Think I'll do like you and Ryano suggested. Glue moderate first and then increase the reflex with the backing. Thanks guys, just a thought experiment...
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Now you're exceeding my mental faculties ;D That does make sense. I was just thinking that pulling strain away from belly and putting it in the tension strong boo might could be a good thing. Less belly strain is less set, right? And I figured the further the limbs traveled backwards the more energy they would store, But if this would pull out the reflex as Justin suggested than I guess my theory doesn't matter. I sure wish I had the time and materials willing to sacrifice to this and just give it a try.
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Nate in book I of the TBB series the chapter on performance(I think) and just before the part about Perry Reflex the author describes a glue up process where you do what you are talking about but with different degrees of reflex with each lam added. If you have TBBI look it up.
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Thanks Pat. Yeah it's TBB3 that has a short discussion about that. But Tim is so unenthusiastic about laminates that the discussion is hardly illuminating. I'm more curious as to what reflexing a deflexed lam would do. I think it would add at least 20lbs >:D ;) But in all seriousness lets look at it another way. If you had a naturally deflexed of 1 1/2" single lam of osage and you glued up 3" of relfex ultimately being 4 1 1/2" of total reflex, wouldn't that store more energy than a straight core that was reflexed 3"? I guess I'm justing looking to duplicate that effect artificially with a third lamination.
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That being said I'm not going to waste that purty set of lams on an experiment. Maybe later :D
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If you have the time, initiative and materials give it a try and report back with your results. ;)
You beat me to it! ;D
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Pat,
If I can get my jointer dialed in and have the ability to make more lams myself I will definitely give this a try. And will certainly report the results here ;)
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Hey Nate.
If you wanted to end up with 3 inches of reflex, with 1 inch of deflex in the handle, you'd have to reflex the tips 4 inches wouldn't you?
I was just reading back thorugh this thread and yes Cam you are right, and that was my whole goal ;D to get 3inches the limbs would have to be reflexed 4" in my thinking resulting in more stored energy without as radical a profile ;D
I wish Badger would weigh in on this, something makes me think he's already tried it....
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I'll bet he has tried it.
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You guys are right, I did try it but I have no recollection of how it came out or what the heck the result was. This was several years ago and a similar discussion was taking place right here on PA but the old sight. I think the idea has merit but I hadn't really developed enough testing skills at that time to really evaluate it properly. I think I would get some red oak or maple and plane it down and try it. I Know that tri lams tend to loose some of the perry benefits but still seem to perform very well. I think it is definitely worth a shot. If you do try it use the no set tiller method when tillering the bow out and it might help to evealuate how succesful the method is. Steve
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One more thought, I seldom do tri lam bows, I usually just laminate a back to a slightly too thick belly, when the belly is thick at glue up I notice that the bow continues to gain reflex as I tiller and then as I get closer to full draw will generaly settle back in about where I started. For some reason I tend to get confused when I start thinking more than 2 pieces of wood LOL. Steve
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Just a thought, to be perfectly honest I would rather my glue lines not be working at all. The less stress you have acting on a glue line the lower its chances for failure (possible embrittlement over time). Second NTD, If I remember my deforms classes correctly, by doing the glue up in two parts you move more of your forces to the inside of the bow, rather than mainly the outside surfaces. It's sorta a force cancellation thing. The belly would be put into compression then pulled into tension, and with any luck you end up with a belly that is under equal and cancelling forces. Your back would be under a greater tensional loading though. However the bamboo would be my top pick for a backing to take that kind of abuse. Just thinking it out in my head makes me want to guess you would take less set and avoid crushing a belly by this method, however if your core lam is not up to the task, you may crush it. Take that with a grain of salt, just thinking aloud, I have yet to attempt it.
Adam
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Thanks for your input Steve. I'm definitely going to test this at some point. It will probably be quite awhile until I have the time, materials and energy to put into "tests" though. About gluing up thicker lams and gaining reflex as you tiller. I saw that with my first 2 BBI's and then lost the gained reflex through poor tillering. The rest of my laminate bows have been pretapered cores and I have still seen that happen early in tillering but not to the extent of those with thicker cores.
Adam,
I personally don't see any benefit to doing laminates unless I were to put stress on the glue line, i.e. Perry Reflex. If I'm just looking to hold down splinters there's plenty of other backings I'd use.
Your analysis is exactly what I was hoping for but wanted to see if anyone had some results not just theory. Didn't want to waste these lams on an experiment.
Thanks for the input everyone.
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I has always been said that by using 3 lams instead of 2 you are defeating the peurpose of the perry reflex. I think enough bows have been built both ways now to show that the 3 lam and 2 lam bows perform about equal if made right, even the multi lam bows seem to be keeping up. They are about 10 fps faster than self bows on the average. Well built laminated all wood bows are comming so close to what is considered possible right now their is not a whole lot of room for improvent. Steve
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Steve can you explain how a trillam bow negates perry reflex? Is it that the stress is moved to the midlam rather than the glue line?
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I was never one of the ones to really get into how the Perry reflex worked, i just knew it worked well to glue on a backing that would hold the bow into reflex as opposed to steaming or heating a bow into reflex. The accepted theory behind it may be questionable now or may not, possibly the tri lam bow is doing the same thing even though it was thought that it couldn't. I never have really totally accepted the theory but don't discount it either, sometimes just knowing something works is good enough. Obviously i would prefer to know why and how but you you know how that goes. Steve
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Hmmm. Thanks for the food for though. Makes me wonder if there is any benefit to trilams at except being purty....
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Nate, sent you a PM with a link to a discussion that Dan Perry weighed in on, and it should help with some of your questions.