A kata is a pattern or form used for study or for reference when creating an utsushi blade. The exercise of accurately making kata based on the work of historical smiths is an excellent way to train the eyes, mind, and body to create proper tanto forms. The most important aspect of making kata is to work carefully to be as true to the original lines as possible.
Making a kata is not as difficult as making an actual blade for several reasons. One is that the outline is the only concern as the bevels are not created for kata. Another is that the raw material need not be as thick as it would for a tanto, 1.5mm is enough. And the final reason is that there is no tempering involved as the steel need only be mild and not high carbon. While forging is sometimes possible with thicker stock, the majority of the work is done with a grinder, saw, or file.
Finding a Pattern
Finding an accurate and life-sized pattern is the first challenge in making kata. A photo or outline must have accompanying measurements so it can be enlarged to the actual size. With some basic image-editing skills hi-res images found online may be scaled to match their measurements and printed at 100%. Sword reference books often have oshigata (tracings) of well-known blades for study and a skilled user of an accurate photo-copy machine can produce an faithful reproduction to cut out of paper. I was given a recently published book from Japan which included life-sized photos of several famous tanto and other swords so I was able to trace them directly from the book.
A good starting pattern is the famous and beautiful Aizu Shintogo, downloadable from the soulsmith Pierre. He has precision cut kata available for study as well as more information on scaling and making kata. The photos in the example below are of a tanto known as Shinano Toushirou, by the kamakura era smith Yoshimitsu of the Awataguchi school.
Transferring the Pattern
A simple Japanese metalworking method to transfer a pattern from paper to metal is to dot punch through the paper around the outline. With sheet steel the paper can be held in place with magnets to prevent movement.
Another approach is to cut the pattern out of paper and trace around it, or even to glue it to the steel. In this case I used sokui (rice paste glue) to temporarily attach the tracing paper directly to the surface. Care must be taken that thin paper does not distort the shape, and dot punching should still be used in addition to the paper if you plan on using a grinder or bandsaw as the paper and glue will overheat.
Using a scrap of steel that is already as close as possible to the blade dimensions saves time and material. To do this project with hand tools, hack sawing as close as possible to the lines is much faster than removing all the material with a file. Better to leave some extra than take too much though!
The kata are clamped in the vise and carefully filed to their finish dimensions following the same order of operations as ara-shiage when making an actual tanto. Once the shape is exactly aligned to the paper template it is checked again with the original (or a second paper copy) and any final adjustments are made with a file. Spend as much time as necessary at this stage and be as accurate as possible.
Reproducing accurate mekugi ana is an important feature for identification and historical interest. Many old and valued swords have more than one hole in the tang where they have been adjusted and re-mounted over the centuries. Some may be filled with lead or copper, others are open, some drilled, filed, or even punched.
The holes should be accurately traced onto the pattern, center-punched, drilled and filed to proper shape and size, and filled with either a copper or steel plug to match. The plug can be cut from a rod of similar size and forged into the hole in the same manner as sekigane. Rice-glued paper can be removed after a short soak in water and the scrap steel surface can be left as is, oiled, or even polished.