The Koshirae-nuki*

How to remove tight fitting tsuka on production katana
October 28 2009

* not a real Japanese name / tool, just something I made up :)

In every book about katana or nihonto they describe the traditional pad on the left wrist to remove the blade from the tsuka... Great idea, exect for production katana.

One of the most common issues on production katana is the tight fitting tsuka.
As tsuka are manufactured separately, the shape, depth and width do not always fit actual shape of the nakago. Tsuka are most of the time hammered on the nakago. Hence the many cracked tsuka sold by companies with bad quality inspection and of course the too tight tsuka (the reason why you are here :p ).

As I do lots of maintenance on numerous brands of production katana, I needed to think of something as these bastards never seem to work along.

The nakagonuki works pretty well for blades in shirasaya but since 99.9% of the production katana are in koshirae, I needed to find something else.

Anyway, since I couldn't find any real solutions I started thinking to create a tool which should be this a lot easier. Should you have any comments of ideas, please drop me a line on:
jeffrey [curly email thingy]

Thanks and good luck,

Jeffrey Ching

ps. The only one time that the (traditional) pad on the left wrist worked for me and that's only because the tsuka itself was already split in half.

The Tool

I intend to make a nicer version but for now this works fine. I'm sure that african black wood would give a nicer look but with my limited wood working skills I just used a chunk of pinewood I had lying around.

The piece I had is about 15" x 1" x 1.5" (45 x 2.5 x 3.5 cm)

With a chisel I carved out a groove about 4-5" (12cm). It has a smooth slope that should compensate the curvature of the blade and place the feet of the koshirae-nuki (at least) half-way the habaki. Make sure the width is a little wider than the habaki. I also removed a part of the tool that shouldn't be touching the tsuba (see top picture)

What this tool allows you to do is hammer the tsuka of the nakago almost vertically. This minimizes the chance of damaging the tsuba, seppa, habaki or even the blade itself.
Any force will be directly transferred through the tsuba onto the fuchi and tsuka.

Place the sword in the groove so that the koshirae-nuki has its base touching the seppa. The back of the groove should be touching the mune.

It should now look a little like this. It probably is still a bit wobbly so we need to secure the blade to the tool.
I used a piece of cloth to tie the blade to the koshirae-nuki. Make sure the cloth is big enough to create a padding so you don't cut yourself when hammering.

Once its all secured you can grab the katana on the padding and start hammering on the top of the koshirae-nuki. I use a standard steel hammer and get most tsuka removed within 4-5 blows. After each blow you should check if the feet are still aligned correctly.

Last but not least: I hope you were smart enough to remove the mekugi pins first... :)
As with all DIY projects, be careful and keep using your head.

Jeffrey Ching