Interesting new project

[DC]

Well I'm bummed. It was going just great. I tillered it on the shortest long string I could get on. Tillered it to 14". Took a couple more scrapes and put it back on the tree. Out to 14" then it went to 15 then 16 then 17 and settled out. OK, I thought, I've gotten the surprise over with. Tiller looked great. Pulled it a few times, everything was fine. Reflex had just peaked at 5 1/4" and was now at 5". So I low braced it. Looked good. Put it on the tree, one light pull and it collapsed. A hinge in the top limb. I quickly unbraced it and took a look. There was a thin spot right at the hinge. About 1 1/2" was 10 thou thinner than either side. I could see it in the rings. No idea how or when I did that. I evened it out but I've still got this. When I unstring it and hold it up against the original tracing it looks good very little if any set. It's just very weak there. This one was feeling fast. Tons of early weight. Crap. Why can a spot that is so obviously thin lie in wait and not show itself a little earlier. Because it hasn't taken any set in that spot I might be able to salvage it but it would be very light.

[DC]

I cheated, I glued a new belly on that limb.

[DC]

Well that didn't go well. Turns out the belly I glued on wasn't thick enough to fix the main problem so I quit and ripped it lengthwise on the bandsaw. As I mentioned in the first post I was going to have to leave some sapwood under the boo backing. Well, I estimated wrong and by the time I got to brace height I was very close to having no heartwood left. So I had one boo heartwood limb and one boo sapwood limb. I believe as I was getting real close to the sapwood the scraper was cutting more in spots so it started hinging. Either that or the sapwood is just no good in compression and started collapsing. Or a bit of both. In hindsight if I had sanded the sapwood off that limb I probably would have had enough heartwood to complete the bow. I'm also surprised at how thick the bamboo is. The picture is mid limb and the limb is .450 thick. That puts the bamboo at around 3/16" thick. I'll have to watch that next time. Those knife edges can fool you. Anyhow I learned a couple of things and killed a few days of self isolation so It was a bit interesting even if it was disappointing.

The little strip of heartwood is the piece I glued on. Not much left of it.

[bownarra]

Could you kinda describe your vice tillering method? If I put it in the vice and grab a tip in each hand I'm standing to close to see if it's bending evenly. Right now it's going to 40# with about 1-2" of tip movement so it's kind of hard to pull with my arms stretched out too.

I suspect he is talking about something like what Gordon does in his Vine Maple build thread, post #66:  http://www.primitivearcher.com/smf/index.php/topic,53195.0.html


Mark
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Yes that's right.
Same it folded on you DC. Try adding more deflex straight out of the fades, even glue billets up into the desired shape. I think this is close tot he 'ultimate' recurve profile

[DC]

I've glued about 11° of deflex in the last half dozen bows. I'm afraid that if I put much more in I'll start losing braced string tension. The limbs start to reflex almost immediately out of the fades so the deflex doesn't show much. If it doesn't show maybe it isn't there, I dunno. A quick look at my fastest 3 or 4 bows all have the reflex starting just out of the fades and that's really the only clue I've got other than more total reflex. I'm just about to glue up the next one so I'll try another degree or so of deflex. Then it it's a dog I can blame you