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Bow Post Mortem Requested
Strongbow:
I had a catastrophic failure today with a new bow. It blew up at just over 3/4 draw with no warning. :fp I would love input to help figure out what I may have done wrong. The bow was sugar maple, 60" nock to nock, 42# @ 26". The limbs were just under 2" at the fades and 1-5/8" at mid limb with small static recurve tips. I estimated 22" of working limb. I put about 30-40 arrows through it after tillering and everything seemed fine. I know it may be hard to give a definitive diagnosis without seeing a full draw photo, but that is impractical at this point :-[ From the way the wood snapped on the back is this a tension failure? Did I need to have a longer section of working limb?
Hamish:
60" between nocks, with static recurves, and 1&3/4" wide limbs, is more stressed than a similar designed straight flatbow.
Your timber is figured with fiddleback. A beautiful feature, but the grain is significantly weaker than a non figured piece of maple.
Conclusion: Sudden Tension break, clean across the limb, due to grain structure breakdown after successful tillering.
Solution: Use unfigured, straight grained wood. Also making the limbs a couple inches longer, and or 1/4" wider for the same design would help increase safety.
willie:
--- Quote ---is this a tension failure?
--- End quote ---
yes, sometimes a slight imperfection on the back is all it takes (or one just under the back)
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quarter sawn |__|__|__|__| works good also
Eric Krewson:
I build flintlock rifles with figured maple and have found from rasping and scraping this wood that the dark strips are rock hard and the lighter wood between the stripes is often very soft. I think this is your problem.
RyanY:
I had a very similar failure in some curly ash. My suspicion is the same as Hamish that the figured wood just doesn’t handle stress well.
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