Sunday, November 9, 2014

Diagonal Chumasaru — a small tutorial

I don't know if it's the laptop or all the sawing and planing, but I have a pain in my right hand that has me doing a lot of reading and not so much working.

For sunday monday, I choose some light work then: filing.

For a long time I've been thinking of my diagonal cut kataba. I really like it but it's a disposable blade and it feels cheap when it cuts (but it cuts fast!). Furthermore, I didn't really understand how to make the same filing by hand.

Enters Nagakatsu. He has some lovely nice looking diagonal cut saws that Tanaka is using for 2 years already without sharpening. Yesterday I saw it in use here.

I counted the teeth, and it was 20 at the beginning, then a large gullet every 6 teeth. The tooth on the gullet is a rip tooth, and I guess it has no set. (By way of comparison, my universal kataba has 2 rip teeth every 6 rip teeth.)

So it looks:

I'm sorry about the red handle. It's a spare one I have from sakura pink. Gosh they look kitsch.

So. How you do it?

1. Take a cross cut saw,

2. Count 20 teeth from the base up and break it. I used my leatherman. (You see, I learnt something from all the teeth I broke without wanting to do it: the best way to break them is with pliers.) From then, break 1 tooth every 6. That is, leave 5 teeth between the spaces. One will be rip, 4 cross cut. Alternatively, start from the top of the saw, count 5 teeth, then break the sixth, and go down till you have 20-22 teeth left.

3. Put the saw in the saw vice and start filling the gullet. I started with the handle in my left, and I go from the back to the top of the saw. File the gullet first from right to left, such that you project the angle of the left tooth towards the centre of the saw. Should look like this:

On the right, you see the broken teeth, in the left the filed gullet. In the middle, the steel that flies off the file. Don't worry too much about the left side of the gullet you are filing, you will take it out soon.

4. Once you are done with left teeth, it's time to set the geometry for the rip teeth. They have to be at the very least vertical. So, starting from the bottom left of the gullet, now you file towards the right, removing more material from the side than from the bottom. Wie so:

Again, I go from left to right.

5. At the end, should look something like that. As usual, after some practice it gets better, so I tend to retouch the left side of the saw.

(Those are the hammer marks of when I tried to straighten the blade. Didn't really work.)

6. Then, last step. You need to sharpen the teeth next to the gullets with a rip geometry. This will lower the height of those teeth, since it's at a lower angle than the cross cut . So you also need to sharpen a bit the cross cut teeth to keep the same height along the saw. 

After 10 saws, you should be able to get something like this

That's it. It took me like an hour or 2 while having breakfast. It looks incredible cool and even the red handle looks sexy now. 

It also cuts btw. Still needs another session of sharpening to define better the geometry but today's task is  accomplished: creating the gullets for your own universal cut ryoba. 


  1. Ooooooh! That last photo shows it perfectly..... Nice!

  2. That's Nagakatsu's saw... I hope one day can get close to that. For sure, this is not the last one I try.

    1. Hahahaha! Oops....*Tries to remove foot from his mouth*........

      Sorry about that! The one that you did (the first picture) looks great too. Perhaps I was dazzled by the handle, confused, haha!

      The ChoMasaru mado saw tooth design reminds me of a western crosscut lumbering saw. They have 5 teeth to a group, a big gullet then 1 rip tooth followed by 2x2 alternating bevel. I will be very interested to see how this works for you. It seems like a great use of a troublesome saw (and good practice).

      I will be sending you my saws. A Chilean metate!

  3. Tonight I want to finish the sharpening of that one, I need to severely change the angle of the rip teeth and deepen the cross cut teeth. I also need a small round file to finish the gullets. The one I have is for hard metals and doesn't really work on the saw.

    Let's see how close I can get.

    And you can send as many saws as you want, the service is for free. But you cannot sue me if something goes wrong :P