this step is not terribly involved, but it will provide some reading until the tsuka is well underway...**spoiler alert: sketch below**
This kotanto will have an all wood handle with a samegawa wrapping and no tsuba, so the only additional hardware required is a seppa, a thin metal washer for the habaki to shoulder against. The outline of the seppa will determine the profile of the handle so it is very carefully planned in the context of the finished project.
The opening in the seppa should be large enough that the tang does not actually touch it but small enough that the habaki can cover it. A punch is used to spread some material from the the top and bottom corners and they are adjusted to grip the corners of the nakago mune and the nakago-no-gata. The final patina will be a similar fired copper shu-do to the habaki.
Copper water pipe is annealed in the forge, split with shears, opened, and hammered flat. (this strip has already been cut in half, this pipe will open to about an inch and a half)
A rough opening is cut with a small chisel, as large as possible while still leaving enough room for a clean filed edge, and then hammered flat again.
The nakago-ana is enlarged and cleaned up using escapement files. As with tsuba, even though this will opening be hidden from view, making a lovely shape is considered a valuable contribution to the overall aesthetic.
Measuring from the top and bottom of the habaki rather than from the opening, the shape is laid out and chiseled, cut, or filed, and the edge refined on waterstones. The final size is based on a small edo period tanto fuchi that measured 34mm x 20mm. I took it down to 19mm in order to slim the proportions just a bit more but did not go further as the corners of the habaki on the 5.5mm wide ko-maru mune are already within 3mm of the rim on either side.
The finished seppa provides measurements to sketch out the rest of the koshirae. I have not done the final shu-do patina on the seppa yet, this will allow some forgiveness while working on the rest of the koshirae. This is usually the first point in a project where i begin to sketch in earnest (but because size is so critical to this piece, the dimensions on the top of the page were laid out before forging). The first sketch is based more on the kaiken tanto form as well as the piece that originally inspired this one, but since this project has blossomed into a proper aikuchi with the heart of kaiken, the second sketch is based on formal aikuchi tanto lines and has enthusiastic approval as the direction this is headed...
...next up, tsuka!
). Thank you again for this great showpiece!