Friday, January 9, 2015

Correct me if I'm wrong — straightenin a one dimensional saw

This comes after some really good explanation Jason gave me and hope he agrees to publish  here. 

Today, I will be focusing on the firsts statements of Mark's instruction to straighten a blade:

1) work from both sides

2) work by halves - sneak up on straight little by little

3) don't focus on a couple square centimeters

Again, enters physicist mind. First, let's assume we have a one dimensional saw, not too useful in the real world but works for illustrative purposes. That's a line. Second, assume that the length of the saw is not affected by the straightening process. This seems sounded to me, but it just an assumption.

Figure 1 shows several lines that have the same length, doesn't look like but they are. Or I say they are and you just trust, ok? If you remember from calculus 1 the length of a curve is given by the integral of the square root of 1 plus the square of the derivative. Wiki it if you forgot it or never had calculus. If you don't like math to the kitchen and grab a rope, then do the experiment yourself. 

Fig. 1: Several same length curves.
Looking nice, isn't it? That's my theoretical saw for different amounts of hammering.  Let me take a look step by step.

First, you start with a bump in you saw:

Fig.2 Initial bump

You hammer it from the top, say at the right of the peak. With that, you reduce the bump but create waves:

After one hit

Now to fix this you need to hammer from both faces (up and down), and you need a few more hits, from both sides (left and right). Eventually you end up with something like this:

few hits later

Great, the bump is gone but now the waves are all over the place. So you see, you cannot focus on 2cm only, you need to look at the whole saw.

If you keep on hammering, side by side, and from the left and right of the original bump, eventually you end up with something much more similar to a straight saw.

final "straight" 1-d saw

Now, in 2D this will be the same but the waves will spread radially from the original bump and they will interact, so you need to consider that to attain a global straight saw.

The previous reasoning has to hold true if there is no substantial elongation of the saw when hammering it cold, and it's independent of how you do the hammering, this is only a geometrical characteristic of the material. To say it in another way, I have no idea how to do it, but I know that if I can make it, something along these lines needs to happen.

The next step would be to properly understand how and where to hit the blade in order to obtain the desired deformation and how the properties of the hammer and the anvil influence this. Once you understand that, you can make a plan.

That's it, does it make sense?


  1. Haha haha haha!

    You, my friend, are nuts! Stone cold crazy.....I love it!

    This is actually a much better representation of what I was thinking, and corresponds well with my development of thought. You read my mind!


    I need a rope......


    1. I've been working on my clairvoyance lately. I think that the length of the rope remains constant because the waves are only the product of stresses inside the material, there is not much deformation as when you are forging it... or that's what I think anyway.

  2. I knew you were working on your clairvoyance! Some endeavours in life require crazy, and this is one of them.

    Yataiki once took a 330 mm blade out of tempering oil that looked like dried lasangna before boiling. I gave him a look, couldn't help it - and he wailed that thing flat, less than 2 min. With a small chipped face hammer. I'll never forget that, never. It was like watching a hungry tiger feed. Seventy years young at that time. (1998)

    The kanji: Ya = great/excessive; Tai = crazy/weird; Ki = energy/spirit

    1. Great name and great story, would love to see it.

      Have you tried forging your own saws btw?

    2. I haven't. I have everything but a building for it all to go into. I've seen the process, and also the making of Yariganna. Also have Nokogiri blanks and pieces for about 200 saws, mostly 210 mm ryoba.

      It makes no sense to make the saws if there are no files; one might meditate on the interdependence of artisans of the past, and the atomisation of communities in an industrialized, modern, and post-modern world. Seems like the files are drying up.

      The reason the building doesn’t exist is a marriage that didn't work.

      Zigged when I should have Zagged.

    3. In one of the posts I counted the number of carpenters per 100 people in my dreamt village. It was one I think. Then you need one blacksmith for the tools, one saw sharpener, one file maker. Lumberjack, bread maker, tailor... you catch my drift no?

      Most of the energy-intensive work is already done. We can order carbon steel by internet and with a few hundred euros get enough for a life or two. And written word makes for a faster learning too... what I'm trying to say is that you need a scene.

      Sorry to hear about the marriage, it's a difficult thing.

      I was thinking of getting these, maybe we share them? I can ask murakami to send each half

      For what I've seen during the week I guess you can get 100 files in a few months. How many do you need per saw?

    4. brief reply: I have used Kaku Matsu brand files before, but this type of file pictured, while sometimes used for dozuki, I don't use except for finishing, and I didn't see Yataiki use them even for that.

      I'll have to send some pictures by email of what I use, with some notes.

      This is Tsuboman brand (a pot with kanji for "even" ect., has connotations of katana jargon) inside. - However these are double sided, for Zuranngata Nokogiri - don't know what saw that is.

      I only use single sided files.

    5. Altho 20 files for $12! how much more for shipping and fees?

    6. I've never used a single sided file, are they much more comfortable? Can you go to smaller teeth with them?

      The total price of the auction is 3 times that after shipping, roughly. Gets expensive but at least you can get them.

      I saw the others you linked, but I have enough large files for my not so many bug saws, so I'm passing on those. Please do send the pictures :)

    7. I think for crosscut teeth, they are the only way to go. Rip teeth can be done with a two sided file, with care.

  3. After a bit of reflection I see what you mean. It is the same length though the shape is different. The final "straight" line is what we are going for.

    In practice, we are not hammering blades enough to change the dimensions.

    We may dent a blade, of the less hard variety, that's their nature. Western carpenters worked their saws this way, and the evidence is there. Sharp Straight Western saws cut impressively. They don't hold an edge as long, they leave a rougher surface, but unless you saw very slowly and carefully, marking out exactly, you are cleaning up with a nomi.

    I restored antiques for years, and used nokogiri daily, because they speeded up the work, and so used them even more frequently. But that was only after they were done by a professional. As I bought them, they wouldn't cut straight, because even though they looked straight to me, they weren’t.

    This is also true of disposable blade saws - not guaranteed to be flat.

    Don't be surprised if i seem fixated on this subject. I'm really a woodworker, though I've worked in iron/steel, clay, and stone, and brick/mortar.

    In woodworking, minor adjustments have major consequences.

    With saws - the same, only an order of ten.