Primitive Archer
Main Discussion Area => Bows => Topic started by: Eric Garza on October 05, 2023, 05:01:32 pm
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I have been playing with hickory-backed osage bows, and am planning on trying my hand at a bamboo-backed osage bow. The osage boards I have bought have all had pin knots. Are there particular pin knot orientations that raise the risk of failure particularly high? I just finished a HBO, for example, where there is a pin knot running across the belly of one of the limbs. It has held up so far, but I fear it will fail at some point and am unsure how many arrows I will be able to put through it before it hits the end of the line.
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Treat pin knots on laminated bows just like you would a self bow. By this I mean if there is a knot compensate for it by leaving extra wood at that point, either in width or leave a raised bump around the knot. If you don't then you risk chrysalling. Sometimes you get away with it, sometimes you don't. Since my approach changed to always compensating for these knots I haven't ever had to deal with chrysals on laminated bows.
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Hamish is correct, but I also believe in trying to avoid the problem before it ever starts by planning the design and glue up to minimize the issue. To that end I try wherever possible to select boards that are plain sawn so that knots are oriented belly to back. Where that isn’t possible I try to design them so that knots never run out from belly to the side of the limb. If you have a knot that runs from side to side, orient it as close to the back/neutral plane as possible and keep meat on the compression side, like in the picture below.
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I have not found pin knots or runout to be a problem in bamboo backed bows unless the wood is edge grain, then pin knots are a deal breaker when they run side to side on the belly of your bow.