Need Advice on First Backed Bow

[barebo]

I'm getting a Hickory backed Ash bow at a stage that I think is close to floor tiller. I'm looking for high 40#'s. The limbs are 1-1/2" at the fades and taper to 7/16" tips. It's 70" NTN. The Ash growth rings are nearly 1/4" thick. The Hickory backing strip is 3/16". My 2 questions are this - well actually 3. Do I leave the backing perfectly flat on the edges, and look for a rectangle cross section for the limbs, or slightly rounded??  How much Ash would you guess I need in thickness, or do I need to just put a long string on it and get it bending ?? What would be the tiller profile for a straight taper narrow limb with stiff handle. Should I go for elliptical, or get it bending right out of the fades?? Thanks to Medicinewheel, I put some Osage tip overlays on, and a Walnut-Osage-Walnut handle overlay on it. It it starting to look nice, and I want it to be a shooter !!! Maybe get a pic up soon. Thanks - all input appreciated!!!

[sulphur]

this is my take on it.  round off those corners,  limbs will be as thick as they need to be (somewhere around 1/2 - 9/16 ")  its a hard to say every piece of wood is different.  the thickness will have a gradual taper as you achieve good tiller.  I think your tiller profile should be more like a ELB.  Not bending so much towards the fades.  since its 70" long it should work well.  but not whip ended, if you know what i mean.

[snedeker]

Sulphur's advice is exactly what I would say.

Dave

[barebo]

sulphur, I was leaning towards that type of tiller - basically have a really narrow pyramid limb - straight taper from fades to tips. Seems like it wants to bend mid limb right now. I'll thin it down a bit more before I put the long string on it.