Primitive Archer
Main Discussion Area => Bows => Topic started by: RyanY on December 24, 2016, 12:18:28 am
-
I had this weird idea about a way to possibly increased stored energy in a laminated bow. The idea is that gluing laminations that are twisted into a straight profile would increased stored energy. For example, in a bow with four lams the back and belly could be normal but the middle two could be steamed and twisted in opposite directions before glue up. Of course this would increase the chances of twist in the final product with increased difficulty in keeping everything symmetrical. But would gluing twisted lams together increase stored energy for the bend of a bow? Just a crazy idea I'll likely never try but any thoughts? Has this been done?
-
It might but sounds like more hassel than its worth unless you had nothing better to try. I can imagine it being overly diffucult to get right with minor benefit.
-
sounds somewhat like perry reflex but more wonky
-
Stored stress in a direction that can't be released to do useful work?
Del
-
Ryan the glass guys are doing something like with woven carbon. They also like to take wood veneers with opposing cuts and glue them together believing they are making more energy.
-
Just a gut feeling, but I would tend to agree with Del about twisted. The larger question, of improving ways to store more energy in prestressed laminations, might still have more room to run.....
-
Good to see you back Dr. Yoon. Are you going to make it to the Classic again?
-
I guess it makes sense that the rotational stress probably wouldn't contribute to stored energy for a bow. Thanks for the input!
Clint, I'm hoping its in the cards. Going to be a lot going on next year starting residency so we'll see. I'm praying that I can make it!
-
I have never really accepted that the prestressing of the laminations is what gives the laminated bow that little extra boost it has. I think it has more to do with less hysteresis do to the bow being strained less while acquiring its finished profile.
-
Good to see you back Dr. Yoon. Are you going to make it to the Classic again?
+1 :)
DBar
-
I have never really accepted that the prestressing of the laminations is what gives the laminated bow that little extra boost it has. I think it has more to do with less hysteresis do to the bow being strained less while acquiring its finished profile.
It would damage the wood a lot less if we just glue in the reflex instated of preforming the laminates through heat bending and gluing them.
One way to test the effect of pre-stressing would be to make two identical 4-part laminated limbs; and make one by gluing in reflex with all 4 laminates at once and compare it to the other that was made by first gluing the 2 laminates each flat and later glue the two flat glued laminates into reflex. The former would have three pre-stress glue lines while the latter would have just one. But I don't do laminated bows. At most I make bamboo backed bows, still very rarely. I might try the test by making two same shape siyahs.
-
Would a perry reflex be an example of this?
I alwayd wondered about the unwinding of a twisted limb during a release. I figured that the angle of force would not be tangential to the plane of the string. There would be torque but I don't think it would translate the energy to the string and arrow.
Snowboard makers have cross grained wood cores in order to increase strength and breaking resistance, they call these X-grain so that the grain lines up 45 degrees opposing the laminates. This is more to solve breakage from the forces being at 90/perpindicular to the edge of the snowboard. You could store more energy before breakage this way.... off topic....
I had made a higly reflexed recurve that caused the string to fly off and would go past the arrow pass, I wondered if was allowed in flight archery to do this, as it increases stroke length and releasing all stored energy (including energy stored in brace).
-
I agree, great to see you back Dr.
-
cool idea!I like to think up unique designs also.
-
Good to see the Dr in the house
where you doing the residency
you best show up at Marshall son
as for your question man its Christmas I ain't stressing my brain over it right now I have Grandkids to play with
see ya in the spring my friend
-
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.
-
No idea on the question ??? but good to see you back on Doc. ;) :)
Pappy
-
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
-
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
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.
-
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.
-
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.
-
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! :-)
-
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.
-
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.
-
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.
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.
-
I do notice that bows with a laminated back tend to be a little thinner than self bows.............. get strained less
Sometimes, these bows actually end up physically more massive
Astute observations, guys. Good food for thought