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Overcoming failure is a big part of bow making and something that all beginning bowyers must face. Last weekend was the first time I have ruined a stave. Sure, I had made some sub-par bows before: bows that turned out weaker than I wanted, or that had inefficient designs, but they could still shoot. This latest stave I straight up ruined. And it happened right as I was putting the finishing touches on the tiller.
It all started last winter when I harvested a beautiful Bitter Cherry (Prunus emarginata) round from our local woodlands. I field split it into quarters, working through the cold, drizzly afternoon. As soon as I hauled the wood back to the barn I covered the ends with Elmer's Glue to prevent over drying and set to work peeling off the bark and cambium. I wanted the back of the bow to be the outside ring of the tree. Peeling the bark is easiest when the wood is freshly cut.
This is what the raw quarter looked like before I stored it for drying. As you can see it had some character to it. A slight twist in the grain and a gentle amount of curve at one end. I let it dry for about 6 months in my room (our wet Washington climate makes outdoor drying even slower than normal). I checked it with my moisture meter regularly and it hovered around 14-12% for the majority of its drying time. When I moved this summer my bow staves ended up getting left in a hot car for about 36 hours, which dropped their moisture content down to 9.5%, the ideal range for starting work. Car drying on a hot day is a quick and easy way to achieve kiln dried results as long as you closely monitor the rate of moisture loss. Luckily, no checking or warping occurred.
Here's a picture of a worked down stave (right) split out from one of the quarters (left). At this point its about 1/8th of a log. I cut it to length (about 62") and drew my bow dimensions on the back in pencil. I chose a design with a narrow, stiff handle and wide, flat limbs. After that I started to adze down the sides to get the correct width and taper. I left it about 2" wide from handle to mid limb and then gently tapered it to 1/2" nocks. After a lot of rasping, adzing and sanding it started to look like this...
The red part on the handle is the heartwood. At this point it started looking pretty good. I had adjusted for the slight twist in the limbs and had both of them bending pretty evenly. But then disaster struck...
Those little white lines running across the limb are called chrysals or compression fractures. I spotted them as I was coming down the home stretch of tillering. Just as I got the draw length up to 28" I heard a soft *crunch*. I immediately eased off my pull on the string to prevent a full bow-splosion. Here's a close-up view of the stress fractures
These little buggers happen when the structure of the wood fibers collapses on the belly surface of the limb. Basically the wood fibers go from a spring in compression to a crushed aluminum beer can. The spot hinged noticeably and I don't think I could draw the bow again without it having a blowout.
In hindsight, I think that I could have had a less robust handle fade-out (the area where it transitions from thick narrow handle to wide thin bow limb). A smaller fade-out leaves more length on the limbs and allows them to distribute bend more evenly. I think on my next attempt I will not try to correct the slight twist in the grain, since it seemed to screw up my tillering process. The main lesson to learn here though is just plain old patience. When it comes to tillering, take it slow, and always remember that you can't put wood back on!
Bummer! What was the draw weight at failure? Do you think it was over-strained? I wonder if having a rounded belly instead of flat would have helped.