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Ahh so Ken san knows quite a bit about the materials, good work Ken!

Anyways, The bamboo used for the back is always left untreated by heat but belly and core laminations were heat treated.The backing is 1 1/8" wide and 1/8" thick at handle and tapers in thickness very slightly to the top tip but tapers to almost nothing on the bottom. Width is 15/16" at both tips. The backing covers the whole way of the bow, but the belly does not. The top tip has 6 3/8" of belly exposed and bottom tip has 4 1/2" exposed. Also, the belly wood is notched so that the belly wood and bamboo belly have a meeting area. Rattan is wrapped under this notch and should be a little lower in height than the notch itself.

Their method for heat treating for the belly lam was to "smoke" it for one to two years until it reached the desired color, usually a light golden brown, sometimes a bit darker. After this, the bamboo was stabilized and could be scorched (heat treated with coals) without bulging.When the inside bamboo is smoked it is called susutake and when left plain its called shōtake The type used is madake (Phyllostachys bambusoides) and the circumference used for the backing/belly is 18-21 cm and 30+ cm for core bamboo. The dimensions for the belly lam is around this: 1/8" thick with no thickness taper, and 1" wide, tapering at both ends to about 7/8".

The core is made of several things depending on the period and what type of yumi it is. The following woods have been used in the core as either the side lams or inside the core itself with bamboo: Mulberry, waxwood/sumac (Rhus succedanea), catalpa and birch, but I have only heard of one reference of using birch in the bow so I don't know how common it was in yumis. Sometimes, figured wood is used for the side lams but this is probably not common or only for special bows. The bamboo in the core was tapered so that the side lams would not run out when width tapering, which is only very slight. Core dimensions are 9/32" thick at handle, over all thickness about 11/16". Thickness at upper limb is 3/16" thick below the notch, total thickness of about 1/2". Lower limb core is 5/32" thick with over all thickness of 1/2" also. The tips are spliced in and usually made of some "pretty wood" like figured wood etc and are there to keep the core from moving and to make the tips which are bulbous looking pin nocks. The bottom and top tips are shaped different because they will have different curves to them.

All yumis have staggered nodes, none should be matched together and should be evenly spaced as humanly possible! Usually 7 nodes on back and 5 on belly, this is important. Nowadays, I believe modern glue is used,but original glue is hide glue from deer I believe. Once the core has been glued together and tapered, the backing and belly lams are glued on and clamped using rope and wedge method. There is total of five curves in the bow, one in the center reflexed (strongly), next mid-limbs of both top and bottom are deflexed (very slightly). Lastly the top limb after deflex is large reflex but not sharp. Bottom limb is also reflexed at tip, but not as long as top. The bow has 20"( sometimes more or less) reflex when first made and settles down to 16" (again more or less) later after being shot in. Important note: yumis are made with off centered string alignment to the right side of the bow.

The bow is not tillered, but put on form to teach it how to bend. Then, if severely bad tillered, heat is used to correct (thats why hide glue works best) and I have not heard of it being done,but I suppose if left a tad wider, side tillering could be done.... After the correct shape is achieved, the bow is braced and shot in. Sometimes bow is lacquered clear but also black lacquer is used. Before, they would lacquer the bow black, then wrap in red silk and lacquer over the silk to give it a nice deep red color which is really pretty if done right. Of course if pretty figured wood was used then clear lacquer is best. After the finish has been put on, rattan bindings are put on in between nodes (so Ive seen but not always I suppose) on the limbs,in the handle section and under the notches on the upper and lower limb. Paper is folded at handle to build up the grip under the rattan bindings. (should be a smooth long taper, no abrupt transitions) Depending on the size of the bow (in this case about 226 cm) the handle should be centered 32-34" from the bottom nock.

String used for yumis are constructed many different ways. One way is silk core wrapped with paper and then lacquer. Another is hemp core with woven silk sheath and lacquered over. No string loops are used, but instead a special knot is used..which I don't remember how to tie..... he he he

I don't know how tall a bow you guys might be making, (depends how long a draw you have) use these measurements as starting points. It also depends what core woods you use, how much reflex, how it was heat treated, how short/long the bow is and how far the bow is pulled and humidity. If making a longer bow than 226 cm put the grip higher and lower on a shorter bow. If this is the right length for you and you just want a heavy bow, increase the core thickness.Since this is only about the bow, I will stop here since arrows are not included...unless you would like to know about those too?

BTW, my avatar is not a picture of me, just so nobody mistakes me as a 60 year old Japanese archer lol

-Alex