Rediscovering Lost and Forgotten Knowledge


Do you expect a challenge to lay down before you? No, it never happens that way. More often than not progress in this arena is made by repeated failure of one sort or another, and then the decision to keep on trying. On more than one occasion a problem that seemed almost intractable was overcome, not by some careful deliberative process, but a flash of insight after much frustration. Case in point, the above file, where I thought I was making good progress in my technique, but actually totally missed some crucial points of knowledge.

This type of work holding seems to be great for the larger files, but is really tricky with yasuri.


A lot of the challenge thus far has been how to start with a rough forging and end up with a really nice flat face for the teeth to be cut upon.


Reading an old book on machining from 1890 I came across an improvised surface grinder of sorts, and figured it could hold the key to the accuracy I wanted. This actually works pretty well considering that my grinder isn’t fixed to the table.

It also works nicely as a file launcher, same mode of action that a tennis ball launcher uses, haha. And I caught my index finger under the wheel, which I don’t recommend.

But it misses the point! Sure, I can rather tediously produce a good finish and flat parallel surfaces, but this doesn’t translate to yasuri.


I wasted a bunch of time, trying to save time, making various jigs for grinding the face angles when the hand tools actually turned out to be faster and more accurate. You see, I’m not trying to make files of all exactly the same dimensions. I care about proportion, not dimension.

For example, given a rough forging I start by profiling the thin edges parallel to each other, and then make the length of the file surface five times the width. I don’t care if its a 72 mm file and not a 75mm file. If I am going to make yasuri by hand I think its fitting that every one is slightly unique.


After abandoning the grinding method for finishing the faces I came to the realization that I should be keeping things a simple as possible. Give me all the equipment I want, sure, I could make some decent files. But this is not about re-creating a viable business or modern production process, its seeing what can be done with simple tools, hand work, and skill born of knowledge.

My sen-dai for yasuri is a most elegant example. Its a piece of scrap kumiko with the correct ‘v’ profile planed in, with a small nail at the front that acts as a stop, and some masking tape wrapped around the back that raises the tang a bit so that the clamp can hold the whole length of the yasuri flat on the wood.


As hard as I tried will a flat mill file to draw file the faces of the yasuri flat I couldn’t get there. It would seem as well that the thinner the face width, the harder it is to produce a flat surface.

The problem being the solution, the file must be curved. A curved file can yield a flat surface with the slight innacuracies of working by hand, nothing new to the world, just new to me. Thinking back upon the Nicholson company treatise on files and rasps its clear that there used to exist file holders that would flex a file, as well as curved files, and of course, tapered files, by which they mean a curved taper.

The latter is actually what I want the most, a three or four sided file with heavy curved taper, but what I have on hand is a small mill file that’s case hardening leaves is quite flexible and easy to bend into the curve I need. Once again I kept it as simple as possible.


Reminds me of a double masted sail boat for some reason, haha.


Get that damn high spot down son! I use Dykem layout fluid to show where I’m filing, but a felt tipped marker works just as well.


Its got to be a quality, if I may describe it so dry and technically, known as pretty damn flat. I use my chisel as straight edge with a light behind it to help sight the high spots.

The curved file was a break though of sorts, and with care can get things pretty damn flat, but I need it better.


The curved tip of a jewelers scraper/burnisher finishes things off.


Practice with the file teeth comes slowly when you have to forge and grind the practice material, but I’m making progress.


How about the odd man out? At 50mm its the smallest yasuri I’ve tried to make, tiny little thing!

I cut the right most one yesterday and actually almost did an acceptable job. The thin edge of the yasuri cross section presents an added challenge compared to cutting a flat file. If I was to simply strike the chisel squarely upon the face the tooth would cut cleanly towards the middle and fade at the edge, where the metal wants to yield. So the chisel has to be struck harder on one side than the other. In addition the edge must be quite perfectly supported by the lead underneath or no amount of hijinks with how the chisel is struck will cut an even tooth. If you’ve watched the video from yesterday I’m cutting on a tiny jewelers anvil, which is hardly ideal in terms of hammer response, but allows for a firm clamping situation which is more important.

In addition I could go on and on at length about how the chisel needs to be sharpened in such a particular way. When I started I left a knife edge on the chisel, but that edge is very weak and fails quickly. Besides, a file tooth cut with a knife edge will have an acute corner at the bottom of the tooth gullet that is almost guaranteed to pin and lodge material. The solution as I have mentioned is slightly dulling the edge, but as I’ve found out its not enough to simply round the edge. What I’m using now is a 20 degree back bevel, 25 degree front bevel, and  85 degree micro bevel on the front, maybe three or four strokes across a 1000 grit stone. By blunting the tip straight across you create a strong edge that still allows the ridge of the previously cut tooth to be felt, and the chisel slips less in use.

Up next is yaki-ire, the hardening.

3 thoughts on “Rediscovering Lost and Forgotten Knowledge”

  1. Geez, Gabe.

    Got the world shuddering in it’s shoes!

    Excited for the future, I’m half expecting a post in a week “So, I just finished my kilns and managed to rig up a redneck file-cutting machine. My first hundred files aren’t great, but with some practice…”

    This blog makes Lost Art Press look like a poser!

    1. Thanks guys, it makes it easier for me to spend time on this stuff when I know there is mutual curiosity out there about these things!

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