Why did it break?

[Kidder]

So I had a really cool bow going that I was definitely pushing the limits on my ability on, and not entirely unexpectedly it ended in catastrophic failure! It was a hickory board bow. 68 ttt. 1.75 inches wide but narrowed the last 8 inches - 1/2 inch nocks to 3/4 inch wide at 8 inches. The tiller was decent but far from perfect. I was able to low brace it and pull it to about 22 inches at target draw weight. I then decided to put in some very mild recurve on the last 7 inches. Boiled it for 30 minutes and threw it in a form. I had a brass strip on the belly to prevent splinters from lifting. Let it cool for an hour or so and then let it sit a for a day before I restrung it. The recurve immediately began to pull out so I unbraced it and then heat treated the belly until toasty brown. But the base of the recurves always felt “soft”. I was able to rebrace it and tiller it with 3 trips to the tillering rack. It was strung for about an hour tops. Took the string off and one of the recurves didn’t seem to recover. I put medium pressure by hand on the tip and it blew up at the base of the recurve right where it had felt soft. Pretty disappointed, but if I can learn “why” it happened then it can be a partial success. Any thoughts? 

[bownarra]

I wouldn't call it 'blowing up' but bending a bow backwards is a sure fire way of breaking things. Once belly wood has been compressed - stretch it at your peril
Design your bow from the outset. If you want a recurve make a recurve from the start.
If you are new to this then definately follow the K.I.S.S. rule! Make a simple flatbow. It will shoot plenty fast enough if you tiller it well.
Your recurve pulled out because either you didn't heat throughly enough or more likely it didn't have any extra thickness to keep them stiff.

[sleek]

It ain't broke, just a little damaged. Fill that dude with wood glue, and clamp it back together. Then, don't try and recurve a bow anymore until you have done with scraps successfully.

[Eric Krewson]

It's toast, I did exactly the same thing on an old osage bow the other day, go it too hot, too dry, the limb was very thin and it snapped when I put it on the form.

[bjrogg]

I think it was a bit thin in the tips for static recurve. I usually bend in my recurves earlier in the process and try to thin them as much as I can, but they need to be thick enough to hold their shape. When my outers are bending just right, I thin my static recurves to just slightly thicker than outer limbs. It’s a game I play. To thin I lose and recurves pull out. To thick and extra Unwanted weight.

I agree that it probably can be saved. Use some very thin super glue. Soak it in that splinter. You could put a underlay on the belly side of recurve over the splinter. That area shouldn’t bend anyway.

Eric has posted some very attractive underlays . Maybe he can give you some tips.

Bjrogg

Oh I see Eric just posted and doesn’t sound very optimistic

[sleek]

I think it was a bit thin in the tips for static recurve. I usually bend in my recurves earlier in the process and try to thin them as much as I can, but they need to be thick enough to hold their shape. When my outers are bending just right, I thin my static recurves to just slightly thicker than outer limbs. It’s a game I play. To thin I lose and recurves pull out. To thick and extra Unwanted weight.

I agree that it probably can be saved. Use some very thin super glue. Soak it in that splinter. You could put a underlay on the belly side of recurve over the splinter. That area shouldn’t bend anyway.

Eric has posted some very attractive underlays . Maybe he can give you some tips.

Bjrogg

Oh I see Eric just posted and doesn’t sound very optimistic

Underlay is a good idea too. Normally I'd say super glue would be  best, but with the size of the crack he would probably appreciate the extra working time.

[PatM]

After wood has been cooked by boiling it  breaks quite readily if you keep bending it the same direction, especially if you add heat to it in that scenario.

  Try hitting a recurve on the belly side with a heat gun after boiling it  while adding a bit of pressure.  It will yawn right apart.

[willie]

recurving the tips makes the inners work harder. stiffening the tips does the same, and shortening the limbs does also.  repair and add some thickness back to the tips.

an underlay sounds like a good way to reinforce the repair at the same time.

[Eric Krewson]

Here is a repair I did for a split limb, been shooting it for years.

[Eric Krewson]

This was for a crushed, cracked and broken limb tip.

 

[Eric Krewson]

I guess my "toast" comment was a little premature depending on how much work you are willing to put into the repair. I spent a week fixing Julia's bow with the crushed tip shown above.

I made the bow I broke fro my brother-in-law, he died of MS and the bow disappeared. It was found abandoned in a storage locker strung with an electric fence wire string. It wasn't much of a bow at this point with at least 6" of string follow. I was heating out the string follow and retillering it when it broke. The bow was about 20 years old and from a time frame when I didn't make super good bows. It wasn't worth the effort to fix it.

[Kidder]

Eric - that is a gorgeous repair! I’m definitely going to give it a shot. Got nothing to lose but time...Are there any links to a more detailed description on how you did this?

I’m still a little unclear on then”why” though, but it seems like a good bet that they were too thin when I put the recurve in (maybe a little uneven as well) and that rather than hardening the recurves to prevent them from pulling out I likely made them brittle by heat treating them more. Also recurved them too late in the tillering process. Does that seem like the consensus?
Thanks!