Now for the bad news. After resetting the brace on his string, he pulled the bow a few times and we heard a "tick" sound. Never a good sound for a bowyer. I checked the bow over and couldn't find anything wrong with it, but I put it on the tiller tree just to be safe. After a few pulls, BAM the bow let go in the inner third of one limb. I have a couple of pics, one of the broken bow and a closeup of the break.
In doing the autopsy, I think there are two things that contributed to the bow breaking.
One was the fact that there was a bark inclusion a couple inches inside the break that we left a little thick. It was just outside the fades and should have been bending there, I thought we had a little bend but maybe not. When the bow was 67" n/n I think we still had enough limb without this few inches of limb.
The second weakness, was something I did wrong. When I was heat-bending the one billet to get rid of the dogleg, I accidentally scorched the back of the wood a bit in one spot. You guessed it, the spot was right where the bow broke. I've had trouble before, having the heat wrap around the blank when it is on the form and cause the back to get a little brown. I had worried about the spot initially, but as we went through tillering I figured it was OK. Apparently not OK when you have 60lb of stress on that short a limb.
What I think happened, was that the browned area became somewhat brittle and popped when subjected to the combined stress of a 60lb bow with a limb that was not only short but even shorter due to the thick spot in the inner limb. If you look at the closeup of the break, you can see a few short breaks running perendicular to the length of the limb, right in the region that was the most scorched.
Needless to say, I was pretty bummed about this. Jimmy took it in stride, he's an easygoing guy thank goodness. We are getting together again on Tuesday to regroup and start another project.
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