Primitive Archer
Main Discussion Area => Bows => Topic started by: ShorterJ on March 12, 2021, 01:25:42 pm
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I’m practically done with my first self bow, but about 6 inches from my fades there is a tiny compression crack coming from a pretty deep knot hole. It seems to have traveled a tiny amount the more that I’ve shot it, but it’s still probably less than an eighth of an inch. My question is are these types of cracks typically issues? Do they tend to travel until failure occurs, or do they crack a little then stop after the stress is relieved? I left the area around the knot thick and wide to try and prevent stress. I’d hate to put superglue in it just to preserve the primitive aspect, but I don’t know any alternatives other than leave it. The bow is of hickory, 60 inches ntn, and is a pyramid design. Thank you all for any help!
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I notice now that the crack isn’t visible on the post, but it’s in the bottom right of the knot on the first picture.
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I see tool marks, not sure about the crack.
The limb is so thick there I have a had time imagining it bends enough there to fret. If it is a fret I'm not sure if glue would fix it.
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Try and get a better picture of it.
A compression fracture will have its edges 'raised' when the bow is braced, enough that you can feel it. Unfortunately there is no fix for them.
When you have a knot like this do not leave it thick, just add the 'extra' width where the fibers flow around it. When you leave a knot thick like that you automatically stress the wood either side of it too much. The effect can cause a compression fracture on the handle side of the thick bit.
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Put super glue in it and see if it changes. Will you post a pic showing the bow braced and full draw and indicate on each where the crack is?
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I tried to get some better pictures. Should I remove some thickness from the knot even though my tiller is about where I think it should be? In both pictures the crack is located about six or seven inches from the fades on the upper limb; it’s coming from the handle side of the knot. Or did you want pictures of the crack at brace and full draw?
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Forgot the pictures here they are.
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Your tiller looks pretty good. I think that is a check radiating out from the knot. I'd say fill it with super glue and shoot the bow. Keep an eye on it just incase.
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If it was a compression fracture it would run across the limb, not along it.
Del
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If it starts to get any bigger I’ll probably use superglue. Sorry for incorrect terminology; I thought it was a called compression crack. What would it be called? Just a knot crack? Thank you all for your time and help.
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The big knot is in the worst place that is most stressed in the limb. I would have tried to put it in the handle. But that is not always possible.
Anyhow it might not be the compressive stress that is causing the crack. Can it be just a drying check? How well is the stave seasoned? Have you been measuring its mass weight?
Even without fully understanding the mechanism at work, I would ground out the portion of wood which just cannot bend with any reasonable amount of compressive power.
Can someone read the following and explain it in ordinary language, please?
https://www.researchgate.net/publication/289961696_Effect_of_knots_on_the_bending_strength_and_the_modulus_of_elasticity_of_wood
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I don’t think it’s a drying check because I examined the knot extensively throughout the process and never noticed a crack until I started shooting the bow. The stave was seasoned for a few years, but I am unsure of how dry it was kept because I got it from someone else. I have not been measuring it’s mass weight either.
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I can't see a crack but the tiller is too good. In other words, when there is knot of that size the knot I tiller the limb to appear slightly stiffer in that area. Just to keep the knot from bending too much. Jawge
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I’d probly say that it will be fine.... not a chrysal/compression fracture...
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It's a check, a drying crack.
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Those happen. Most of the time they don't amount to anything. shoot it and keep an eye on it. It probably wont change much if at all.
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Don't worry about it. Superglue won't do anything to help. Just make sure it has a good finish on it as water can get in those type of cracks.
It cracked there because the wood around the knot is very different to the rest of the wood in the limbs.
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Definitely get sealer deep down inside knot hole and crack to prevent moisture out. I don’t think the crack itself will be an issue, but would keep Ana eye on it just in case.