Backing shape

[DC]

What shape should the cross section of the backing be? An even arch like a bamboo backing or just rounded shoulders? If I'm a little doubtful about the backing is there a shape that would minimise splinter lifting?

[leonwood]

Depends on the backing and how thick it is. If you have a backing with a single ring that would dictate the cross section and just needs the edges rounded.

If the backing is quarter sawn and really strong compared to the belly wood I guess rounding it or even trapping will work really good.

Now I have used lots of hickory and ash backings an always made them flat with rounded edges and never had one fail. Used it on many belly woods from heavy hardwoods to yew and black locust

[DC]

It's quarter sawn Hard Maple, about .140" thick on a Black Locust bow.The grain is straight looking from the back but I'm afraid there may be some run out front to back.

[Marc St Louis]

Besides rounding the edges I never round or trap a wood backing

[Springbuck]

  I agree with Marc.

 I think you need to be darn picky about selecting stock for backings, saw them as well as you can read and follow the grain, and then trust the backing.   I round any hard square corners, and I often trap, but I'd leave the rest alone.

[GlisGlis]

It's quarter sawn Hard Maple, about .140" thick on a Black Locust bow.

just a thought.
Isn't Maple going to put too much stress on BL?

[DC]

I wondered about that but all I've got for backing is Bamboo and Maple. I'll trap it a bit and we'll see.

[PatM]

It's quarter sawn Hard Maple, about .140" thick on a Black Locust bow.

just a thought.
Isn't Maple going to put too much stress on BL?

 Doubt Maple has greater tension strength or stiffness than Black Locust itself.

[willie]

wouldn't thinning the backing be preferable to trapping the bow if you were worried about a specific defect?

[DC]

When I think about this I always seem to fall back to "the outer 10% does 50% of the work" or whatever it is. Seems to me the rest is along for the ride especially when they are similar woods. If, as PatM said, the Maple is actually weaker than the Locust in tension then trapping may not be necessary or even desirable. Now that I've confused myself even more, does trapping reduce the draw weight? I'm sure it must but I'd better check. I'm tillering now, not to brace yet but the limbs are down to less than 1/2". .140" Maple and .360" Locust. Time to think about narrowing the limbs I think but that will narrow the belly. Hmmmmmmm

[Springbuck]

 I agree DC. 

Maple may not be as strong as BL, but maple is tensions stronger than average. also, a pristine BL back is stronger than it needs to be, so as long as the maple is strong enough.

According to TBB, trapping lowers draw weight a tiny percentage, lowers physical limb weight a higher percentage, and prevents set.  I think preventing set comes more from design and appropriate draw eight.

BL only 1-1/2" wide, I would NOT narrow the limbs, except of course to taper.  If I liked what I was seeing, I would trap.