Hey Mike,
I'll be back in a few with some info to get you started.....
Alex
Ok here is what info I have obtained from my research so far.
Bamboo used: madake
Side woods for core: zelkova
bird's-eye/tiger maple
buckeye
wax tree/sumac
mulberry
catalpa
Siyahs or nock woods: ebony
peach
cherry
Core
The core is made up from 5-7 strips of heat treated bamboo and side wood made usually from figured wood or wood with attractive color. They do not say why they use the types other than for beauty of wood appearance but they prefer the wood of the sumac or mulberry. Depending on the type of yumi, the core can be as short as 221 cm (Namisun) or as long as 245 (Hasun-nobi) and goes over the siyah/nock wood.
Dimensions for Nisun-nobi (226 cm yumi):
Forgot the draw weight but it is around 18 kg or 40# with draw length of about 95 cm (37")
The core is 7.35 mm thick at the grip and 28.5 mm wide. It tapers in thickness towards the upper nock to 5 mm and is 25 mm wide. The lower core tip is 4 mm thick and 23.5 mm wide.
Backing/Belly
The backing runs the full length of the bow and is not heat treated. At the grip the backing is 28.5 mm wide and 3 mm thick. At the upper nock it is 25 mm wide and about 2 mm thick. The belly is 23.5 mm wide at grip and 3 mm thick. It is does not seem to taper on the upper limb, but the lower is thins out to almost nothing, no width taper. The belly does not extend the full length or the bow but stops where it meets the siyah/nock wood at both tips.Please keep in mind these were taken from the side of the bamboo or edge, because of high crown the bamboo should be 1 mm thicker than what I wrote is measured from the crown. They do not trap the back nor the belly, but gently round the edges to create circular cross section.
Nock
The siyahs/nocks are not bent to shape, but cut to the appropriate curve. They are made so that they have a shoulder at the end where it is the same height of the bamboo belly. This area is wrapped in rattan and usually cannot be seen. The upper siyah is about 17 cm long, including the shoulder and same width as the back at the joint then it tapers and flares out at the pin nock shoulders where it is 25 mm wide. thickness varies as different bowyers carve differnt shapes. Most of the time it isnt much thicker than the limb itself. The bottom nock is 12.25 cm long and designed similar to the top nock.
Glue up
The yumi is traditionally glued up using hide glue from a species of deer, however most bowyers now have turned to modern glues for ease in making. I assume you already know the rope and wedge method so I wont go into that. The yumi is glued into five curves.The first is At the lower tip which is reflexed, next is lower midlimb which is deflex. Next is reflex in the handle. Next after handle is long deflex in upper midlimb and last is long reflex at upper limb tip. In its glued shape, the bow should have 45 cm or reflex. After the glue has cured, you must cut to final width and make the nocks. (the bow should be glued up a little wider than the final dimensions.)
Tillering
You don't, well not in the sense that we tiller.Tillering a yumi is done by bending in a form or heating of the limbs to conform to the right shape. Through experience, you will find the right amount of reflex and deflex to make perfect tiller. This is why it takes 15 year apprenticeship to master the yumi!
The only places rattan bindings are required in a yumi is at the joint of the siyah and belly strip on both tips and at the grip, other areas are wrapped for aesthetics reasons or for warbows where they serve as protection. Also, the brace height of a yumi is 15 cm.
Alex
