Here's some of the construction info:
I had splits of bamboo 7.5 feet long and about 1.25 inches wide. It was quite thick and still had the nodes on it. I wanted to make a bow with a boo back, a boo belly and a boo lam between them. A boo, boo, boo...
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Note that a traditional yumi has a boo back, boo belly and a center lamination made up of 3 to 5 thin strips of bamboo with thin wood veneers on the edges. I was going to replace all of this with one flat boo strip.
Using my stationary belt sander and hand belt sander I sanded off the nodes (inside of the splits) and made two of the splits flat on the inside. These two were going to be the back and belly of the bow. I did not do anything to the outside (power side) of the these two splits. From some of the things I've been reading, perhaps I should have heat treated the belly boo so it would be better in compression. I was going to use a torch to put a pattern on the backing boo, but I forgot (actually, I got antsy to get it done and just skipped that part).
On the third split, I sanded both sides flat. The third split (the flat one) was going to be the inside of the laminations. I also thinned the middle split towards the ends so that it was about half as thick at the ends as at the middle. This was done so that the bows tips would be lighter and move faster. For my next bow, I will do the same thinning to the ends of both the belly and back boo.
Next I slathered on the smooth-on and wrapped the parts with saran wrap (to keep the glue off of everything). I then wrapped the lams with baling twine (got a roll from Home Depot). Start at one end and wrap all the way to the other end and then back again. The wraps should be 1 to 1.5 inches apart. When wrapping back to the end again, be sure that the wrappings cross in the middle of the lams.
Once that is tied off, drive wedges into each place that the wraps cross. I used pine wedges that I got at Home Depot for about a buck for 20. Split them in half and sand them down in half length wise to get a wedge that will work easily and not break. The wedges are what 'clamps' the lams together AND supplies the shaping for the bow. No clamps are necessary wtih this method.
The lams will bend away from the side of the bow that you drive the wedges into. So for a deflex put the wedges on the back of the bow and for a reflex, put the wedges on the belly of the bow. Once you've got the wedges in the wrappings, use your leg to bend the bow over to get the reflex or deflex you want and then drive the wedges in further.
I waited a day for the epoxy to cure and unwrapped. Looked good. I sanded off the excess epoxy and evened up the sides with my belt sander, cut out the pin nocks of the bow and decorated it with embroidery floss (the wrappings on it) and put on several coats of shellac to keep the wrappings in place.
The tiller is not quite right in the lower limb but the only way to correct that is to thin that limb so that it bends more evenly over the entire length of the limb.
The bottom limb is 1/3 and the top limb it 2/3 of the 84" length. The final width is just about one inch by .5 inches thick at the handle. The tips are 5/8" wide by 3/8" thick.
As I said in the original post, this was a proof of concept project. Learned a lot and will change some things for next time. Got enought boo to make several more.
I'll try to take pictures of the process next time.
Note: I borrowed a copy of the Jaap Koppendrayer video and watched that once to see how the wrap and wedge thing worked.
It seemed to work really well and you have a lot of fine control over how the shape will turn out. Plus since the bow is not locked into a form, you can pick it up and eyeball the shape and check to be sure you're not getting any twist into the bow.
Pics below are of another project but will illustrate things....
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