This is going to be a post with a lot of pictures, hopefully it won’t take forever to load on your web browser. To start, a method for measuring saw plate thickness, basically a red-neck deep throat dial micrometer using a drill press. By setting the zero on the dial to the thinnest parts of this saw I could write the deviation in thousandths directly on the plate, a grid of numbers. Supposedly this kind of saw plate variation of thickness for western panel saws is unusual, but it offers me a good opportunity to discuss the Japanese tools used to hand thickness nokogiri.
With the grid of the saw mapped I built up a topographical map to better visually represent the variation in thickness. After all, if you’re going to scrape a saw evenly you need to know where to take off metal. This saw already went through quite a bit of hammer straightening, but the problems with the uneven thickness of the plate are making it difficult to get that last 10% of straight. The normal fashion for gauging proper thickness on Japanese saws is to bend the saw and observe the curve, and I can attest that this is, with appropriate experience a la Yataiki, an extrememly accurate way to thickness saws to within a thousandth of an inch, based on some of his saws that I have looked at with the dial micrometer.
The tools used to scrape the saw plates are sen. You’ll find that these were once very common tools to all of the tool making blacksmith trades, including katana and kanna. Some of the sen pictured here are specialized for saw making, like the one at the very bottom of the frame, but there are others that could be used for hand scraping the ura (hollow) on the backs of Japanese chisels and kanna, or the flute on the sides of a katana.
This particular set uses laminate construction with Swedish steel.
And the final stage of scraping involves a lot of work hand burnishing the surface with a lot of pressure and elbow grease.
What kind of Swedish steel I would very much like to know, seeing as saying Swedish steel is about as useful as saying they are made from high carbon steel, there’s a lot of different kinds out there these days.
Lets start with a frame of reference for what the hell I’m talking about. This is a photo of Yataiki thicknessing a saw at the sen-dai. Beautiful metal shavings, no? The sen-dai comprises both the board the saw is resting on and the staple vise used to hold the saw flat. The large staple goes over the sen board and is mounted into a foundation block of poured concrete in the ground, a large block about two feet wide by four feet long, very stable.
For holding the saw down flat to be scraped on the sen-dai there are lots of little spring clamps and wedges. These are all used under the staple of the sen dai. The ball bearing is for rolling vigerously in hand to prevent blisters, the loop of steel is a way of binding the handles of a pair of tongs when forging. The little rectangular wedges hold the sen board against the wedge beneath it that gives it the proper downward angle for work.
For holding the opposite side of the saw nearest where you would be seated are more spring clamps, elegant little pieces of spring steel that slip over the edge of the sen board.
Saw makers don’t make one saw at a time, its more of a production affair. Here is a good stock of rough forged blanks, ready for rough grinding after the tangs are forge welded on.
An elegant spring clamp in use.
And under the staple the various wedges. The spring wedge holding the tang down has a curl at the other end used as a snell, for tapping the wedge loose.
This is just a mock up of the sen-dai. There is one size of board for larger saws.
And a smaller, thinner board for dozuki. Both of these are made from Kashi, Japanese white oak, the same wood used in plane dai.
The staple spring clamp for dozuki have a variation with a little stop cut at the end that the blade butts up against.
That allows for working right up to the end of the saw plate.
In the past all of the thicknessing would have been done by hand. More modern methods involve a rough surface grinding to remove most of the excess material. Here is a ryoba saw, rough ground and tempered. Beautiful colour.
Apparently dozuki are differentially tempered, softer along the tooth edge.
What you’re seeing here is a dozuki blade that’s been hammer straightened after tempering with two different kinds of hammers. Fascinating surface!
Note: This post has been edited to correct an earlier mistake, referring to Japanese Oak as Keyaki (a type of Japanese Elm) instead of Kashi.