trapping black walnut?

[Living_waters]

Has anyone tried trapping walnut to see if it helps with fretting?

I have a pile of staves from a large limb with some good growth rings and deep sap wood. I hate to back any wood with rawhide or linen if I don't have too.

[Art B]

The rounded/crowned back of the stave itself produces a sort of trapping effect. A lot depends on just how round those limbs are I suppose........Art

[Living_waters]

I dont follow, wouldn't the crown make tension strength higher, which is what you are compensating for with a compression weak wood? see if i got this right or if I am confused... trapped for compression weak     with the top being the back.

[Art B]

Trapping has several purpose IMO. Physical weight reduction, lowering the compression plane. Compression weak would is just that, weak. Or it just can't take the compression. So by lowering it's plane, you're making it thinner, allowing it to bend further without the risk of damaging the belly side.

As I mentioned, a crowned surface already gives you a trapping effect. A crowned surface also concretates the tension load right down the center of the back of the bow. The natural trapping effect of a crowned back lowers the compression plane allowing the belly to bend in a tighter arc.

Problem you're facing with a crowned back is that concretrated tension load on the back of the bow. You already have your trapping effect, you just need to reinforce the weakest point. And that's the crown of the back. Best defense, backing! Art

[Living_waters]

Just having a hard time wrapping my mind around it. The fibers in tension on the back increase with the surface area, but by increasing the surface area you spread out the tension stress on the fibers. If you narrow the surface area you are increasing the tension force on the fibers available but reducing the compression force. This is the way I see it, the more tension strength the more compression force.

When I have made walnut bows in Pyramid style, they fret in the lower portion of the limbs where the tension force is the greatest and bend the least. An old bowyer has should me how he compensates for this by keeping the limbs wide until the last 1/4 of the limb. He says it spreads the tension load but also it gives it more compression area, which in turn spreads the force over a greater area.
 

So by lowering it's plane, you're making it thinner, allowing it to bend further without the risk of damaging the belly side.

I understand this, that is why a rounded belly increases compression, but would not a wide flat belly have more compression strength? or better said spread the compression force over a lager area?
Problem I have with backing 1. is I hate to back anything that don't need backing. and 2.backing a compression weak wood don't help it become less compression weak, in fact it may increase the problem, that is why you don't see boo backed black walnut bows everywhere. The backing just helps from getting a limb up side the head........ unless you add a belly lam hmmmmmm

Oh just a note here, crown is not that great, limb was all an 18" bar on my chainsaw wanted.

[Art B]

"When I have made walnut bows in Pyramid style, they fret in the lower portion of the limbs where the tension force is the greatest and bend the least."

Outer portion of the limb is the last place I would expect a limb to fret. Inner limb takes the greater strain, mid-limb somewhat less and the outer or near tips area very little.

If your walnut stave is clean on it's back, and you have good tillering skills, little if any trapping is warrented IMHO if you don't intend to back..........Art

[Living_waters]

by tillering skills do you mean master of the gizmo?  

[Art B]

I don't personally use a gizmo myself LW. I apply a taper and let that produce my profile. For a retangular limb design that you described, I would apply a belly taper of 1/8" from fade to mid-limb and then carry that measurement onto the tips. Using a gizmo on non-dimensional material such as staves can cause some problems IMO........Art

[Living_waters]

I used to cut tapers, but after several unfixable errors caused by who knows what, I let the tiller determine my taper. With a straight stave a 4inch gizmo really helps me fine tune, it helps to see the 1 inch spots that need scrapped. I have not found it a problem on a stave as long as you use it like it was intended.
just goes to show that trad people are a diverse people, like draw knife sharp or dull. My draw knife is the sharpest tool I have and it is the only tool I use to chase a ring. One of the osage gurus would fall over if he heard that. LOL

[NYArrow]

Not to burst into the conversation...but have you considered heat treating the belly to increase compression strength?

[Art B]

LW,a couple things that I read years ago that Paul Comstock wrote in his book "The Bent Stick" that truely holds water. One, good tapering produces good tillering. Not the other way around. Second, your most durable bows will be those where a taper is first applied, and not altered except to change profile.

Yes, heating treating may be an option. But if I were to go to that much trouble then I would certainly add a backing to protect my investment in time and trouble. That's just me though......Art