Primitive Archer
Main Discussion Area => Bows => Topic started by: mmattockx on April 06, 2020, 08:12:47 pm
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First off, i have read the sticky thread about the mechanics of limb twist and it was very helpful for explaining what is going on. I'm working on a red oak pyramid bow. Got it bending pretty well, pulled to 22" on a short slack string. Both limbs have a bit of twist in them when drawn. Since I ran into this on my first bow I was somewhat wiser this time and caught it way earlier. Spent all afternoon trying to straighten them out by working the strong side of the limb down. The right limb I have almost dead true now but the left looks the same as when I started. I took a bunch of wood off the strong side to where I can easily feel the difference in thickness with my fingers across the limb width but almost no improvement in the twist. The left nock is off center of the handle by ~1" when drawn as shown in the pic. I do realize that the right limb is stronger but I wasn't worried about evening them out today, I was just trying to get the limbs pulling straight.
(https://i.imgur.com/BqLPKsT.jpg)
Am I missing something or is there another way to approach this to get that difficult one to pull straight?
Thanks,
Mark
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just get the sides even.
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Check the thickness from one side of each limb across the belly to the other side. My guess is one side of the limbs is thicker than the other. Probably even the opposite sides on the limbs giving an overall propeller twist.
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Check the thickness from one side of each limb across the belly to the other side. My guess is one side of the limbs is thicker than the other.
They were even and that was with the twist so I was removing wood from the strong side. If I even them up I will get the twist back.
Mark
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hi mark,
could the problem be closer to the handle than where it is noticeable?
you might rip a slat of pine or something to duplicate a limb (that bends true), and deliberately create a twist to see where the cause is relative to the effect
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Clamps used as levers ,weights and a heat gun will take out alot of twist...
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hi mark,
could the problem be closer to the handle than where it is noticeable?
Yes it seems to be. I was scraping the inner 2/3 of the limb, leaving the outer 1/3 or so alone. That worked for the one limb but not the other. I will go back to it tomorrow and level off some of the side to side taper and see what that gets me. I still have a fair amount of wood to work with as I am at draw weight at 23" on the slack string. The left (weaker) tip is moving about 9" and the other one is less than that so there is a ways to go yet. I have been trying to clean up the twist without going any farther to leave myself a decent margin at the end.
Clamps used as levers ,weights and a heat gun will take out alot of twist...
The thing is there is no twist when unbraced, it all comes in during the draw.
Mark
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For example..
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Be sure thickness is even and then heatgun and twist. I made two bows from neighboring parts of a thick board and both had the same tendency to twist when braced, each limb in the opposite way. The first one I screwed by trying to adjust thickness - did not work at all and the bow finished light - the last I heated and twisted and it is all good.
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Heat and countertwist as mentioned. Sometimes you can even twist it without heat. Just like straightening arrows.
A lopsided thickness bow to correct twist just looks bad and probably stresses the wood unevenly.
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Some wood apparently has stress in it and will twist when strung, all the scraping in the world won't untwist it. I always use taper lines on my bows so I know the sides are even, when on of my bows twists when strung I don't waste time scraping on the strong side, I get out my heat gun.
My current bow is just such an animal, it shoots great but the slight twist in one limb annoys me. I plan to correct the limb, this will open another can of worms because it is a static and untwisting the limb will get the tip out of alignment. I have multiple heating sessions getting the tips in perfect alignment, guess I'll have to do it again.
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At some point the twist is not effecting performance..I have had bows start to untwist a bit with shooting
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What kind of twist is it? Propellor? All one way?
Was it there when you started (natural)?
Jawge
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A lopsided thickness bow to correct twist....... probably stresses the wood unevenly.
not if the cause of the twist was a variation of density in the limb.
preexisting stress is a different problem, as Eric points out so well
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I doubt varying density is a significant factor.
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Pat, I mention it as something for the Mark to consider. Red Oak can have excessive soft earlywood, Its location and orientation could be a factor. Even with diffuse porous woods, I notice areas that are softer and harder when scraping.
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Be sure thickness is even and then heatgun and twist. I made two bows from neighboring parts of a thick board and both had the same tendency to twist when braced, each limb in the opposite way. The first one I screwed by trying to adjust thickness - did not work at all and the bow finished light - the last I heated and twisted and it is all good.
This seems to be exactly what I have here. I will clean up the limbs to even and then see about twisting them opposite to the way they want to move.
Some wood apparently has stress in it and will twist when strung, all the scraping in the world won't untwist it. I always use taper lines on my bows so I know the sides are even, when on of my bows twists when strung I don't waste time scraping on the strong side, I get out my heat gun.
So do you twist it past center in the opposite direction to the way the limb wants to go, sort of preloading it to pull straight when drawn?
What kind of twist is it? Propellor? All one way?
Was it there when you started (natural)?
Jawge
It is propeller twist, the nocks go in opposite directions. The board was straight when I bought it and warped in one direction after acclimating to my shop humidity levels (looked like reflex after I glued the handle on) but no twist. It still has no twist when sitting unloaded, the nocks move as the bow is drawn.
not if the cause of the twist was a variation of density in the limb.
It doesn't seem to be the case since both nocks move in opposite directions more like propeller, but there certainly is significant variations in density through the early and late wood rings.
Thanks to all for the help, at least I know I'm not alone and this is a fairly common occurrence. I will try twisting with some heat and see if I can get it to level off.
Mark
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So do you twist it past center in the opposite direction to the way the limb wants to go, sort of preloading it to pull straight when drawn?
Sometimes limb twist doesn't seem to affect shooting. If you choose to correct, I would try to minimize any torquing apparent in the hand on the draw. Even propeller twist may not create torque.