Tsuka core dimensions

[Richard338]

My katana blade is on its way back from Peters so I started making the Tsuka (handle) core.
I have three pieces of terotuf stacked to make the core. The outer two layers are 1/4" and the inner layer matches the 3/16" blade thickness (total of 11/16" right now). I left a bit of extra around the profile until I get it inletted and glued and bolted together.
I'm attempting a "haichi" shape which is narrower (in width) in the middle by flattening on the "ha" blade edge side and following the curve of the blade on the "mune" spine side.

I've noticed that some first attempts seem to end up with a larger than desired handle, so I'm trying to avoid this. I also need to allow for the rayskin and ito wrap with menuki which will only make it thicker...

Does anyone know if the core is typically made thinner in the middle as well as narrower?
Anyone know any typical dimensions?
I made it 10" long and it is designed to fit into oval fuchi (collar) and kashira (butt-cap) that are 1.6" on the long axis.
Thanks for any input.

 

[Stacy E. Apelt - Bladesmith]

I have found making the core about 1/4" thinner than the desired size is about right to compensate for the same' and ito. As an example, if you want the tsuka to be 1.5X1" oval, make the core 1.25X.75".

Most first time tsuka start the size desired and end up too large. Another first time error is making the fuchi and kashira the size to fit the core … forgetting that the same' and ito will sit above it.

 

[Richard338]

Thanks Stacy.
I thought that mine is haichi following some descriptions I found http://yakiba.com/Tsuka_shapes.htm
I have the one straighter side and one curved. I will have a larger fuchi (right side of photo) than kashira.
I was allowing about 0.1" for the same' and ito, but I'll increase that to 1/8" at the junctions (1/4" in the diameter).
I guess I'll see how it feels after rounding the edges into oval before considering thinning it at all.

 

[Stacy E. Apelt - Bladesmith]

Best way is to lay some ito on your same' and measure it. A lot depends on your same' thickness and type and the ito used. I use raw same' (hard and white) and a good weight ito. I did a leather wrapped tsuka that I had to take down even more because the leather ito was much thicker than the silk stuff.

I stand corrected, Your shape is hiachi. I removed my earlier explanation.
I had learned it as hiachi having a continuous taper from the tsuba and rikko as having a similar taper with narrower center. In the way I understood it, both had a straight mune side continuing the line of the mune, and a taper on the ha, following the line of the ha and taper of the nakago. Your page states the mune as tapering and the ha side as straight. I looked at a few other sites and that is how they show the shapes, too. I guess I had it backwards in my head. See, old dogs can still learn stuff.

 

[Richard338]

Thanks again, and thanks for the clarification. Yes, I have the hard white same' and silk ito (both from Fred Lohman).
Maybe I'll mess around with a wooden model core before grinding off too much from the terotuf.