Diagnostic issue w/ pics

[simson]

That scetch by Pearl is a good explanation of the failure, too much tension stress concentrated on a short area.

What I'm always thinking of looking on those construction is: where is the tension zone, neutral plane and compression zone. I've seen diffrent proportion of belly wood and backing, sometimes the backings are thin react probably like a rawhide backing (most of the tension is in the main wood). But sometimes, like yours the backing strips are thick and tension is defintely there. For me (don't have access to hickory) boo is the only option, as there are strong running through fibers on the high stressed area.

[leonwood]

I agree with Simon and DC, try bamboo on your next one and leave the higly stressed midlimb area a little wider. My last few glue ups I made them a little wider mid limb also because I noticed the previous ones took a little set in that area. The transition from deflex to reflex is usually the most stressed area I guess

[upstatenybowyer]

Thanks guys. I'm pretty sure it isn't wide enough in the area(s) of highest stress and that like pearly said the curves need to be spread out as much as possible. I'm gonna try making my own backing strips out of hickory.

[Bayou Ben]

I don't have much to add to the already great advice given except that I've had bad luck with maple backings from boards on these designs.  I know Marc uses maple with good success in high stress designs, but I believe he is harvesting his own trees.  Same exact design, maple backed bow exploded, bamboo back made a nice bow.

[Parnell]

If it were me...I'd be wondering if the time and effort I'm putting into the project is worth kiln dried board backings vs. biting a bullet on good bamboo backings.  Just sayin...good luck.

[upstatenybowyer]

I feel you guys big time. It may not be the quality of the backing, but if there's even a chance, Parnell's right, with all the time and effort I'm putting into this, the kiln-dried stuff may have to go. 

[paulsemp]

I've never had problems with kiln-dried Hickory backings. Before I glue them on I always take them and bend them in a complete circle or close to it. An eighth inch piece of wood 6 ft long should not break. considering both of them broke at the same spot I would rethink your glue up methods and or your tillering process. Bring it to Elm Hall next week and we'll take a look at it

[George Tsoukalas]

I think PD hit on the main problem. I'm just wondering why you would back a wood like BL which is already strong in tension but medium in compression, upstate. Maybe the maple should be a belly wood. Don't know as I avoid wooden backed bows. Jawge

[Stick Bender]

+ 1 what Bushy said its hard to tell from the pics but it looks like a delam in some of the pics , how did you glue up ?

[upstatenybowyer]

Jawge, I used BL cause I had billets. I saw DC made a successful maple/BL bow so I thought I'd give it a shot.

Stick, I did the glue up by wrapping in innertubes, then bending into reflex w/ the rig pictured above. I used Smooth on. The lines looked good, and I don't think I starved the joint cause I can's see the innertubes doing that. 

[DC]

Just out of curiosity, how thick are your backings?

[Mark Smeltzer]

Everyone above gave good advice on things to look at.
One thing I make sure of with any bow is that the back is in nearly finished condition. No dings, scratches and especially no square corners. I round mine off pretty good.  If narrow the limb while tillering go back and radius the corners again......as many times as it takes.

[upstatenybowyer]

Hmm, hadn't thought of that Mark, thanks. 

DC, 1/8"

[Stick Bender]

I agree if you use rubber band/tubes ,I can't see enough pressure to starve it providing enough epoxy was used ! The mystery continues  I have been using less and less  smooth on at glue up  the more bows I do but I use clamps or fire hose !

[bushboy]

It still looks like delam in the pics.how do you prepare your surfaces?