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.    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]

is this a tension failure?

yes, sometimes a slight imperfection on the back is all it takes (or one just under the back)
                                _{____________}
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.

[Strongbow]

Thanks for the feedback.  It is helpful to know about the issue with figured wood, but disappointing since I have 7 more staves from this same tree.  Can I still use them for lower stress designs or am I better off converting what I can to gun stock material and using the rest to make maple smoked BBQ?

[RyanY]

Could try backing them with another lamination, raw hide, or sinew.

[willie]

It is helpful to know about the issue with figured wood, but disappointing

before assuming too much on account of the figure, it would be helpful if you were to share more about the staves

did you cut and season them yourself?
are they split or sawn?

was the back of the bow the outside ring of the stave (just under the bark)?

[Strongbow]

It is helpful to know about the issue with figured wood, but disappointing

before assuming too much on account of the figure, it would be helpful if you were to share more about the staves

did you cut and season them yourself?
are they split or sawn?

was the back of the bow the outside ring of the stave (just under the bark)?

Hi Willie,

Yes, I cut and seasoned the logs myself.  The log was ~16" diameter so the crown is pretty low.  I hand split it into over a dozen staves with a sledge and splitting wedges, debarked them within a week of cutting the tree.  The green inner bark peeled off in strips without using a tool, so I don't think there were cut fibers or anything.  I sealed the backs with shellac.  They've been stacked on a rack in the garage and have been seasoning for about 4 years.  The staves all stayed pretty straight while drying.  The back of the bow was outer growth ring right under the bark. 

[bradsmith2010]

those staves may need to be backed,, so much variaion on wood,,it may not be good for self bow,,I would say 66 or 68 would be a better length,, or give you a better chance of success,, gradually go shorter if the next one does not blow

[Hamish]

You could try backing one with clear, straight grained maple, 1/8" to 3/16 thick".
 Its still a risk, as Eric mentioned the differing hardness  between the grain could lead to chrysals. Its one of those things you won't know until you try. I have seen bow wood with moderate curl used successfully, and others that go bang, or chrysal.
Wider limbs always helps reduce the stress.

If you can get some gun stocks out of your other wood, awesome. Otherwise you could successfully use figured material for laminations under clear glass, in a fg bow. Small pieces you could sell on Ebay as spoon blanks, walking stick/cane blanks. Firewood as a last resort, for such beautiful wood.

[superdav95]

You could try backing one with clear, straight grained maple, 1/8" to 3/16 thick".
 Its still a risk, as Eric mentioned the differing hardness  between the grain could lead to chrysals. Its one of those things you won't know until you try. I have seen bow wood with moderate curl used successfully, and others that go bang, or chrysal.
Wider limbs always helps reduce the stress.

If you can get some gun stocks out of your other wood, awesome. Otherwise you could successfully use figured material for laminations under clear glass, in a fg bow. Small pieces you could sell on Ebay as spoon blanks, walking stick/cane blanks. Firewood as a last resort, for such beautiful wood.

Agreed.  It would be a shame to see such beautiful wood burned.  Figured maple makes great knife blade handle scales or hidden tang block handles. 

[ShorterJ]

Seems strange that the break was completely perpendicular to the bow instead of splintering parallel with the grain.  I had some hickory break like that once and decided that the wood was bad.  Both bows I made with that tree broke, and the one that broke like this didn’t even make to brace.

[Hamish]

With fiddleback grain , you get long grain and cross grain . The cross grain is weaker in tension and compression, that's the focus of the break and why it looks as it does. Nevertheless you can still get similar looking breaks in straight grained wood from a comprehensive tension failure, especially when the wood is too dry or contains decay.

[Jim Davis]

I think the wider/longer thinner approach has a good chance to work. Here's a wavy hornbeam bow that worked well.