Ray, I do this all the time. It is one of my fav ways to play with new ideas and materials. I generally use oak cuz the bug bites me and I run down to Lowe's.
Basically, what I do is a lot like you are describing. I have a planing table that I made that allows me to run my power hand planer over a board and take it down to any desired thickness. I am tall and pull long, so I usually start with at least a 70" bow, 2" or even more wide, and a little over 3/8" thick. Perfect boards and backed bows
If the limb's side taper is uniform, even circular tiller is essentially automatic, although wood is wood.
I cut in a narrow handle, and then add fades as short as I can get them, to leave the working limb some length. I add a thin lam (1/8"-3/16")of some "better" bow wood to use as a fade, so I can get it really thin if I have to to prevent the handle popping off. So on oak I would use good hickory or mulberry. On hickory, maybe osage or ipe. Then, you can add little tapered lams on the belly side of the tips and sweep them in from the sides to make a thinner/deeper, lighterweight slightly stiffer tip to make the bow shoot sweet.
On a backed bow, it changes a little. Instead of just a handle with fades, I often put a power lam on the front under the backing. This doesn't work as well with fabric as it does with hick'ry or bamboo. Then the handle on the belly side won't be as likely to pop off. I have used a short piece tapered each direction with a table saw, planes and/or sander, and usually don't go thicker than 1/8". I have also used some thicker veneer, I think it was 1/32" thick, and created a taper by glueing a 4" piece on top of a 6" piece on top of an 8" piece on top of a 10" piece, on top of a 12" piece, on top of a 14" piece. See what I mean? Like a human pyramid. Running a sanding block over it after it dries takes down the little stair-steps, and the backing goes on over that. I do the same thing if I want thicker, narrower tips. Putting them under the backing, not on the belly, prevents then from having to take much load either in tension or compression, and creates a tiny bit of set-back or reflex.
One of the things I like about that there method is that you can get away with a lot in areas you aren't asking to bend as much, like the tips. If you tried putting a veneer on the belly, , esp. where it bends much,it wouldn't work.
Reflexing a pyramid limb will change how it behaves. Both will get the limb working even more close to the handle and in the first half of the limb.
I have had the best luck getting it to a good even tiller (usually automatic with consistent thickness and even side taper) and then reflexing either by adding semi-recurves close to the ends, or by adding a long, even reflex that extends the length of the limb. That kept tillering concerns pretty simple. Middle of the road didn't work well with a pyramid, for me.
I would taper a bamboo backing, or the limb will be getting stiffer and stiffer toward the tips, really overworking the inner limb. This is due to the bamboo's crown. If the thickness is consistent, the limb will be thin at the edges, and crowned close to the handle, but full thickness and square at the tips. A hickory backing that keeps the flat back and belly and the rectangular section might be a better choice.
And BTW, since I draw 29" (and I like it that way) a backing is a necessity on a 66" bow for me. Or I have to go 3-1/2" wide.
A pyramid bow doesn't have to be wide, but the same rules about material selection apply. I could make a long pyramid design in good hickory (I live in a dry climate) and go 1-3/4", but if I was trying to make a 66" or even a 64" out of oak, I wouldn't dream of having it less than 2-1/2" wide. At least.
Even with the thick spots added, The tiller is predictable, if not automatic. I put it on the tree and carefully bend it just far enough to see it bend a little. The backed bow I just described; thickened handle with fades and stiffened tips, will bend right off the fades first. From there, if I need to get a TINY bit more bend, I just take a little off the sides with a plane. If I need a bit more, I scrape the belly a little. Or, I take the belly corners off just barely and take the belly flat down next, kinda like the faceted tillering method.
You will never get away from having to adjust tiller a little, esp. if the handle is below center, or whatever like that. Just watch that handle bend a touch and chase the tiller out from there.
The last one I made, linen backed, was @ 7/16" thick, 68" long, 2 1/2 at the widest, glued with 2 layes of linen into 3" of reflex, with veneer-stiffened tips with a handle and a single piece power lam about 1/8" thick tapered down, about 12" long. I restored it to a circular tiller over all but the last 7" of limb tips. I drew the taper to a point and then added lines that started 3/8" wide and ran till they hit the taper lines, so about the last 5" was parallel.
I had to do some minor adjusting at the fades, and some slight belly scraping mid-limb, and some narrowind and smoothing near the tips. I ended up with a rectangle cross section maybe 3/4 of the way out and the belly side of the ends reverse trapped a little and sanded round. I did that mostly to save weight and because I could get away with it.
Topic: Pyramid bow Tillering approach (Read 3567 times)
