Wednesday, August 6, 2014

My favorite YouTube video -or- My sen sensei

The ura is important. You want to buy an old Japanese tool to fix up ...... look at the ura. A nice ura is indicative of a good tool well cared for by someone who understand how these things work. It is necessary that the urasuki initially be properly formed, though.

The urasuki on the "point of a sword" knife that I am making is not good enough.

I can do better.

I have a favorite YouTube video, of the most incredible chisel blacksmith. I watch this again and again.

This documentary is the most complete example of a modern, yet still traditional Japanese blacksmith that I have yet found. Everything is here, forging, heat treating, even talking with an expert metallurgist, this shows how one man makes tools. Modern metallurgic theory, even temperature and visual display, there is nothing else out there that is even close. It has only been viewed 1800 times (about 200 are from me.....really). It is all in Japanese...... Has anyone had a video transcribed and translated? Recommendations?

This guy is a pure joy, and he loves tools. His smile, his pleasure at showing what he does, his absolute happiness and engagement is just so remarkable..... Every time that I watch this, I think "This is it, this is a person who has found something special." I would be honored to use a tool that this man had made.

There can be no one better to emulate and, as part of his process, he shows how scrapes the back of a chisel. He uses a real sen (scraper), so if you want to see one in action, this is your best option. I wasn't satisfied with the work that I had done, so I went to the source for some expert guidance.

On watching the video, yet again, I realized that I was making the classic mistake of confusing process with outcome. I want a nicely formed ura, so I was trying to cut one exactly the way it would look in its finished state. That's not how you do it, and once I broke the assumption apart in my mind, it became much clearer. If you watch the video, you will see that this guy has two huge racks, full of different size sens. This guy is meticulous, but the process must also be efficient..... What was I missing?

It was the wall of sens (sense?). Each is a different size, each is a different shape/arc. The sen's shape defines the amount of curvature to the carved recess, and would be known as a self jigging tool. I needed to reshape my sen to more closely conform to the curve that I want (it's so apparent to me now....).

Also, the tools face angles were off. To watch him carve the urasuki on a chisel, it doesn't require an inordinate amount of force. Granted, the steel has been annealed (softened, it's in the video), but he makes it look easy. You know that this guy's tools are sharp, so I know that if I can get the proper shape to the tool, it should cut well.

The second round went much smoother. A flat arc and experimenting with different face angles is a step in the right direction. When the tool is sharp , and properly ground, the cutting action IS pretty easy. If it's hard work, something is probably wrong.

Some of the deeper scratches from the first round are still visible at this point. I am trying to scrape right to the edge, but no further.

I apply a quick wash of gun blue to darken the whole back area, then take a few swipes with a diamond sharpening stone, just as you always do when you first flatten the back of a tool.

This creates the the flattened perimeter around the carved recess. Carve away the parts that you don't like, then do it again. I did this "darken, carve, then flatten" a couple of times to refine the shape.

I want the recess to be even from side to side, and slightly flat at the bottom.

I also want the recess a touch deeper towards the back, so that as time passes and the steel is sharpened away, a bit of hollow will remain.

 I used a small piece of native stone to de-burr the scraped area, knocking off any remaining metal chips.

The ura is still a little bit rough looking, but is worlds better than the initial attempt. Not perfect, but.... Better.

I file down some of the rough, but leave a bit for character.

The curves were mostly there from forging, but I do want it to be comfortable in the hand.

I want the handle of the knife to have just the slightest bit of clearance to the work surface. This tool is often used to trim a surface flush, so one hand holds the cutting end down, while the other hand controls the cut.

One large question remains....... How much will the blade warp after quenching? I have no idea. I bend the blade opposite the expected direction of change, enough so that the tip of the knife is about 1/8" high, meaning..... I am guessing that it will warp 1/8" over a 5" length. The handle isn't of laminated construction, so it shouldn't warp at all.

Time for the final quench..... The moment of truth.

In the video, the blacksmith shows how he performs the initial forging using a coal (coke actually) forge, then refines the shape in a different, temperature controlled furnace. Possibly natural gas? In any event the main furnace is controlled by a computer (a "micro-computer" he says) which regulates the temperature, to avoid unnecessary grain growth of the steel. Small grain structure is stronger, tougher, and will take a finer edge  than the course grain steel that is the result of higher heat. High heat makes for easier to work, though. The point is that this guy walks the extra mile, does what he must, to make the best tools possible.

While he operates using an understanding of modern metallurgic theory, his equipment is a bunch of old industrial stuff that looks like it was salvaged out of a dumpster. During the course of the interview, as he is showing the computer controlled furnace, you get this great moment where the conversation goes something like this.....

Blacksmith: "And here is the furnace. The temperature control is so important that the furnace temperature is regulated by a "micro-computer" to avoid that nasty grain growth that I was talking about. This box makes this process possible."

Interviewer: "That old thing?!!"

Blacksmith: "I know, right.?!! This old piece of crap actually works! I can hardly believe it myself! But the old stuff still works fine....."

I LOVE this video!


  1. Jason,
    This is interesting. I got into a little thing with David Charlesworth once about this. He recommended the ruler technique on a Japanese tool blog and I said it wasn't necessary and was pretty much useless for Japanese blades if the tapping out was done properly. Chris Hall has been doing some nice articles on dai adjustment that I know you have seen. Also, have you seen this site: ? If not, take a look at the absolutely perfect ura on some of the Keizaburo kanna. Wow!

    1. Hi Dave!

      You have an exceptional eye for the beautiful, those kanna blades are wonderful! I've never actually HAD a new blade, and every time that I see a pristine example, such as those you brought to my attention, it makes me a bit envious. Maintaining a perfect ura requires commitment, and once you slip up, it is gone....... Well that's overstating a bit, but, you know....

      The ruler trick. The tsunesaburo no ura-dashi back design accomplishes the same, basic function of concentrating the honed area right at the cutting edge. The execution is a bit different, I suppose. I wonder how well they sell? That design was intended for HSS, if I remember. I've never tried to tap out a high speed steel blade. It's probably horrible, even when laminated.

      I think that it's a dirty little secret amongst Japanese carpenters that nearly everyone lifts the head of the kanna blade at the finishing stages of honing, the ruler trick writ small, hehe........ Shhhhh!



Like all of us, I am figuring this out as I go, so when you see something that is incorrect or flat out wrong (and you will!), let me know. This is a learning process. Real people and names, please. Constructive comments and questions are very welcome, but hate speak/politics are not! Life (get one!) is too short.

Thanks, Jason