Tillering a backed bow

[DC]

I just had something happen(again) that I have only noticed on backed bows. I was happily tillering away, everything going fine, put the bow on the tree and gave a couple of pulls and one section of the bow just gave a little. I saw it jump a bit as it went. It was fine and then it just hinged. Is this something I should be watching for with backed bows or is this just a coincidence? I had two inches to go. I might save it but it's basically gone I think. This is on my Maple backed Locust. It is a couple thousands thinner where it hinged. There is 1/3 backing and 2/3 belly.

PS No visible chrysals---yet.

[bjrogg]

Could it be a glue problem DC?
Bjrogg

[DC]

That was one of my first thoughts but the join looks good. Any ideas what to look for? By the time I caught up to the hinge the bow was 30# and with the glue there I can't even use it to cook brats

[willie]

visible in the tiller, but no apparent damage otherwise? Has it taken set at the hinge?

could be the "hidden damage" that precedes the obvious, if so,  good catch

[PEARL DRUMS]

I'd say its an under-exercised issue. Just a guess. A few thousandths thickness variation is nothing. A human hair is .003".

[Redhand]

I'd say its an under-exercised issue. Just a guess. A few thousandths thickness variation is nothing. A human hair is .003".

+1  How many times do you exercise/draw the bow after you remove wood? 

[DC]

Willie--Yes it took a lot of set in the hinge and the other limb is the same just not as bad. I think I was scraping too much in one spot. It's an RD an the hinge(s) are about a foot out from the handle. Seems to me the last time this happened it was the same. I'll avoid that spot next time.

PD-- Good thought, I've kind of gotten away from the 30 pulls thing. Time to back up a bit.

Has anyone ever glued a veneer on the belly. I was thinking that I could correct the tiller and then glue a veneer on the belly and live with what happens. There wouldn't be enough to tiller so that would be it. Ahh, it's just a stick, I'll throw it away and start again.

[PEARL DRUMS]

I have glued veneers on belly's with good success.

[Badger]

  DC, I have had that happen on R/D bow more times than I like to admit. That is one of the reasons I started going to full draw weight after each wood removal. Did it happen in an area where you started the reflex?

[Pat B]

I had an osage recurve fret badly(uncommon for osage, not seasoned enough)  so I ground down the belly and added an Argentine osage lam to the belly. Re-tillered and all was good.

[Bayou Ben]

I agree about excersising the limbs.  I find that with backed bows (bamboo especially) it is resistant to change so excersising is more so important to not have hinges pop up. 
I do think thousands of an inch are important. I have read, calculated, and tested that .003-.005” of thickness on a dense belly is equal to about 1 lb difference in draw weight.  So if you had one limb a pound or 2 stronger than the other one I think you would notice the imbalance in your hand or have your pull hook sway one way or the other.  When you make that adjustment and scrape a few times to balance the limb you are making thousandths of an inch adjustments. 

[DC]

Here's some pics. It looks worse in person. Doesn't look like I took any wood off the outers. Not really proud of this. It started out so nice. The reflex went from 1 3/4 after glueup to 2 1/4" after tillering out to about 18" and then all of a sudden it dropped to an inch.

[Springbuck]

"Has anyone ever glued a veneer on the belly. "

 I never have just glued on a bit as a patch, but I have ground down and added a thin belly lam to save a bow.  I did almost the whole limb, though.

[Springbuck]

  How is the whole thing constructed?   Is it all one piece plus a backing, or is it a backing, belly stock, a handle block, power lam, etc....

  The similar experiences I had were the result of something "giving" near the fades when I had too much going on.

 Like I had a power lam, bellys fishtailed at the handle, then I had thin slats making up the handle and dips, plus my backing was 2" too short, so I cut it and let it gap near the handle.  So the backing at the middle stubbed out on the back, then I ground it flat, covered it with an overlay.   The fades or something buckled or slipped.

[DC]

It looks complex but nothing extends beyond the fades but the belly and backing. The hinge is a foot out the limb.