Sunday, June 21, 2015

My nemesis ( Japanese saw straightening #4)

I'm still working on this guy.

My understanding of the saw straightening process is growing by leaps and bounds, though it is woefully far from complete. What value is there in showing you all of these seemingly endless pictures of a beat up old saw? Well, if nothing else, I want to show that this is something that can at least be attempted.

The knowledge gained here is already having an effect on my skill at actually sawing stuff. I am seeing the saw itself differently now. Before, a saw was a tool that was used to cut something. Now I see a saw as a series of tiny knives, held in accord through their connection to an armature body of hidden strengths, tensions and harmonics. A saw is like the UN.

It also could be thought of as a device for honing ones ability to endure frustration, a hateful thing to be fought perhaps? (?)

Nah.....I love this!

Using a straightedge, I map out the areas that are still the most in need of attention.

In reading a thread on sawsmithing hammers, someone posted this excellent reference.

From 1903...."The Handyman's Guide" by Paul N Hasluck.

It frustrates me to no end, that this common knowledge has been all but lost. In my grandfather's depression era world, you fixed things. You took care with what you had, saved up to buy what you needed, but never bought what you couldn't afford. He said that having too much can be worse than not having enough.

I like to think that my grandfather would approve of me working this way. I think of this a lot.

The idea is that each strike of the hammer has an impact on the steel, literally. You can't actually make more steel, you can't really alter it that way. The steel is what it is. What you do have, you can make thinner. Thinner metal would seem larger, would occupy a greater surface area.

A round face affects the steel in a radiating fashion, like ripples in a pond.

You see the little dimples to either side of the hammer strike?

A wrinkled piece of paper is smaller than a perfectly flat sheet. When you impact the blade, you are creating contour that effectively "shortens" the blade.

A cross-pein hammer has less surface area at the point of impact. It's influence is greater, but over a smaller area.

I try to use this to my advantage.

You will notice that I am striking the steel obliquely. In lieu of having a cross-pein hammer, I am trying to angle the hammer blows to most effectively work the steel.

With the largest of the lumps worked down, it's time to think about removing the bow. First, I check against the straightedge.

A good 1/8" out.

Here is where the directional application of force really becomes apparent. Striking along these perpendicular lines causes the blade to bow upward.

This technique was always referred to as "hammer shrinking" the metal, but that isn't what is really happening. You don't "shrink" anything. you are increasing the surface area, at the expense of material thickness. Always remember, you are making the steel thinner every time that you strike it.

In any event, striking along these lines causes the blade to bow upward, away from the anvil. Keep referencing against the straightedge until things are looking very freaking straight. That's what I'm doing, at least.

Checking across the width, you can see that there are still plenty of high spots that need addressing. I don't know if a perfectly flat surface is something that I CAN achieve, it might be nearly impossible, given the prior welded repair, but I want to give it my best shot.

It turns out that these longitudinal undulations (and removing them) are somewhat crucial to the operation of the saw.


So, I got this thing to a state as near to perfection as I felt was possible....I mean flat! No tensioning yet, because I am still trying to figure out the whole tension thing and, while single edged saw seems fairly straightforward, a ryoba is another beast entirely. Anyways, I thought that I was getting close. I felt that it was time to start refining the process a bit.

I took the saw out for a test drive, and low and behold....the bugger bound up. Not horribly, but still.....I thought that I was getting so close! Granted, by this time I have removed nearly all of the set that was in the blade, but I figured that would better allow me to determine where the remaining trouble areas were.

The binding was one thing, but the most alarming aspect of the saws performance was the way that it rocked back and forth throught the stroke of the cut. Obviously there are still some big deviations in the blade that need work. The rocking motion is due to the sides of the blade interfering with the already cut surfaces. That there is no set to this saw magnifies the action, but it still shouldn't happen.

Altering the set of a saw would be an easy fix, would make it work, but it wouldn't work as well as it could. I think that I can do better.


  1. Nice work with the straight edge! I have a similar problem with binding on the osaehiki-noko I made. I draw filed the sides, but managed to make the toothline of the saw a thousandth of an inch or so thinner than the middle of the blade. Talk about making stuff worse instead of better... It was impossible to get it to cut deeper than 1/8"! So I went back with the scraper and made the middle thinner than the tooth line, but still left the toe and heel too thick as an artifact of my scraper technique, which you can feel binding as the saw is used. Do you have a micrometer that can measure .001" or .0001" with vernier scale? I thought I was chasing phantoms until I pulled mine out and could actually gauge the differences.

    1. talking about callipers... I was looking in while in Europe for a thickness gauges, like the ones the violin makers use to dial the thickness of the plates. I never found one cheap enough. For a few saws I have used my micrometer and helps a lot to actually see where the steel is too thick.

      Then Mark commented that the blacksmith checks that by bending the saw...

      Anyway, I have a dial indicator in the house so I think I should be making a gauge when finally have time for tools again.

    2. That's funny, I know what you mean about those very very deep throat thickness gauges for sound boards. I tried to make a mandolin when I was a teenager and that was one of the things I lusted after terribly, right after a set of those little tiny brass compass planes.

      I love the expression on Mamoru Ito's face from the saw making video, where he is bending the saw back and forth. I love the idea of being able to scrape an even plate just by looking at it, but I think the micrometer is the best way to learn what the right shape looks like without someone there to teach you.

  2. Looking back on this post, have you made progress with retensioning the plate after straightening? After one attempt on a ryoba I found that the centre quickly lost tension, so I would guess that to bring it back would require even strikes along both edges. The end state would be tension all down the centre, transitioning to compression towards the edges. Curious to hear your thoughts.

    1. Mike, my apologies for such a tardy response!

      My thoughts on tensioning parallel your own. I have many questions as well, for instance.....

      How large is the circle of influence from the tension strikes? How close to the toothline should we be striking? 1/2"? It would be proportional to the force applied in striking, but maybe there is a optimal range?

      I feel that the act of "tensioning" the saw is actually expanding a localized area adjacent to the tooth line. In use, the force of cutting the wood fibres generates a certain amount of heat, thereby causing the steel to expand. With a floppy un-tensioned saw, this results in buckling and binding. In contrast, a saw that has been nicely tensioned should still perform well during extended use, with the stretched/"tensioned" area reaching a neutral state with the heat expanded toothline. It's a thought (though a horribly worded attempt to explain a simple concept, haha).

      Or, completely different.....

      Perhaps the "tensioning" process introduces deformations in the saw plate that stiffen the body. A perfectly flat sheet of steel is floppy as all get out, whereas a plate that is dented and dimpled is considerably more stiff. In tensioning a western saw, we are told to use a polished hammer face to avoid marking or blemishing the saw body. The Japanese saw doctors seem to have no such fears. Most of the saws I've got show ample evidence of being pecked at by hammers that are quite sharply pointed, leaving a trail of little divots in the steel. Maybe those guys were hacks, I don't know.

      My factory produced saws typically show a faintly dotted line along the length of the blade, maybe 15-20mm above the teeth. This would be a way to induce roller-stretched tension. The saw blade gets run between two rollers, minutely compressing the steel. Traditionally crafted Japanese saw bodies are carved and shaped to have some areas that are thicker (stiffness) and others that are thinner (clearance), but I haven't noticed any pronounced and consistent lines of hammer marks that would be evidence of hammer tensioning. Maybe the carving process also minimizes the effects of saw plate distortion during use?

      I have a pile of fine old Japanese saws now, all of which look to have been worked on by a skilled metate. I sit and look at them, tilt, gaze, and ponder....looking for clues. I'll let you know if I learn anything, but for now.....

      I'm afraid that I've only got guesses and questions. Very little true knowledge. Let's see what we can figure out. Good on you, to be actively searching for answers!

  3. This sounds like a subject ripe for an english language photo guide along the lines of Des King's kanna e-book. While not entirely a mystery, it would be great to absorb the main methods and a little theory from a skilled metate.
    Cheers, Mike

    1. I love the idea, but of course Des King actually knows what he's talking about, and if you guys are waiting on me......let's just say that decades might be required, for me to feel qualified to instruct, haha. I'm embarrassed to even show what Im doing now, afraid that some one might get the idea mistaken that I actually *know* something. I'm just fascinated by so many of these subtly sophisticated,fundamental acts.

      Learning to sharpen a saw is a simple thing, all things considered, but due to the need for increased efficiency, the trade has been all but lost. Even the best saw will need to be sharpened eventually, and it's far easier (and cheaper) to go the route of disposable blades. What I find so saddening, is that once we've decided to go that direction, there is no turning back. We've now obligated ourselves to discarding finite and valuable resources.

      I don't just bugs me that so much precious knowledge has already been lost through inattention and neglect. And laziness, maybe. This is one of those subjects that needs to be learned bodily, through some instruction, close observation, and MANY hours of repetition. I should be working on saws....100...1,000.....then I might know something, then I might feel qualified.

      What I *hope* to be able to show, is that it's not impossible for someone to fix their own saw. If each of us decided to fix just ONE thing every day, not necessarily a saw, but anything, the world would be a different place. We might learn to make buying choices based on repairability, factoring in total life of the item, rather than only based on price. I'm one of the worst offenders. I buy cheap all the time.

      Haha, sorry.....blah blah blah.....


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