Introduction: DIY Kiridashi Knives

About: I am an industrial designer and a maker. I like to make prototypes, unique pieces, equipment and other stuff. In this channel I will show you what I do, and in particular the making of design pieces, with var…

Some time ago, I spent some relaxing days at my country house. I thought to make something with the few tools available there. What I had at hand were some tool steel and a small self-built forge. So I thought to make a couple of Kiridashi knives. The Kiridashi knife is a traditional wood carving knife, widely used in Japan. But it also is a marking knife, used by almost all the Japanese carpenters, as well as a versatile tool for general use.

Translated to English, 'kiridashi' means 'to carve out' in Japanese.

Step 1: Choosing the Right Steel

The knife steels I had at my disposal were some C70 (Aisi-1070) and some K720 (Aisi-O2). I chose to use a 5mm thick K720 because it is harder than the C70 and therefore more suitable for a knife like this that requires little flexibility but great sharpness.

Step 2: Marking the Steel for the Cuts

To begin with, I secured the metal to a desk with a C-clamp. Then, using a paper template and a Sharpie marker, I marked the shape of the two knives to be made.

Step 3: Cutting Out the Pieces

I then cut the two shapes with an angle grinder and a cutoff wheel. This operation is quite simple, you just have to be careful not to bend the wheel of the grinder and not to apply to much force when making the cut.
Always remember to wear all the necessary safety equipment when using an angle grinder. A face shield, in particular, is recommended.

Step 4: Hammered Decoration

I thought I would add a hammered texture on one of the two knives. This is for an aesthetic effect but also for a more secure grip. To do this I used a small forge built by me. The construction of the forge is very simple: I used a coffee can inside of which I poured some refractory cement. The heat source I used is a propane torch connected to a small gas cylinder. I then heated the knife to a red cherry color, hammering it repeatedly over a small anvil, made from a piece of railroad track.
During this operation, the knife tends to bend, so be sure to straighten it as far as possible before proceeding to the next step, otherwise sharpening will become almost impossible.

Step 5: Grinding the Main Bevel

The next step, after wearing all the necessary protections, was to create the main bevel of the knives. To do this I used a portable belt sander, mounted on a table I made.
The bevel should not create a sharp edge, at this point. It is necessary to leave about half a millimeter thickness to avoid ruining the knives in the next hardening step.

Step 6: Hardening

The hardening phase consists of bringing the steel up to the temperature where it no longer attracts a magnet, then quenching in oil. For this type of steel, the ideal temperature is about 800° C (1472° F), which corresponds to a cherry red color. For quickly cooling it (quenching) I used a canola oil at a temperature of about 50° C (122° F). I apologize for the dark image, but it helps to better understand the color of the metal at the moment of the quench.

Step 7: Tempering

Now the steel should be very hard so that a file should skate right off of it without leaving a mark. But it is also brittle, so it is necessary to temper it to give it some elasticity.
Not having to make the knives particularly flexible, but opting for more hardness, I put them in the oven at 200 ° C (392 ° F) for 60 minutes.

Step 8: Pre-sharpening

At this point, the knives can be sharpened. After the hardening, however, it is necessary to avoid overheating the metal because too much heat on the blade will damage the heat treatment previously made.
The belt sander can still be used but with a fine paper, a low speed, and continuously wetting the blade in fresh water. As you can see from the photos, I do this with bare hands so that I can immediately feel any increase in the knife temperature. First I flatten the bottom of the knife, and then I sand the bevel until it meets the flat surface of the underside. This is a pre-sharpening because the final sharpening have to be done manually afterward.

Step 9: Final Sharpening

For the final sharpening, I first used some diamond stones, up to 800 grit and then a couple of Japanese water stones, up to 6000 grit. For the final polishing, I used an abrasive paste on a leather strop.

Step 10: Final Shots

Here you can see some shots of the finished knives.

In the video on my YouTube channel, you can also see the cutting tests I've made to see the functionality of these knives, as well as have a better perception of the various steps.

Thank you for checking out this build.