Category Archives: Metate

Sen and Sen-Dai for Hand Scraping Saws



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.

Making a Saw Setting Spider


Time for working with a new saw! This time its a 5-1/2′  two man cross-cut for felling and bucking, cuts on the push and the pull, with four cutter teeth to every raker. I’d been needing the use of a larger capacity saw for bucking logs prior to ripping with my whale noko, because my madonoko isn’t really meant for cuts over about half a meter. Now, I’ve made some pretty epic cuts larger than that with time and patience, but even after careful straightening by metate Mark my madonoko still wanted to wander on the opposing side of the cut, and it gets to be a real struggle to layout for boards on the end of the log when the surface of the end grain is concave.


I’ve resisted the idea of two man saws for the simple reason that its damn hard to find another guy to get on the other side of the saw. If you do, damn, that’s a good friend, I tell you!

But a saw like the one in the picture above can be used by one person quite effectively as long as the cut is plumb.


And! There’s some very interesting tools used in dressing these large saws accurately. The jig at the top of the picture above does three things. First, it can hold a file in a curved shape for jointing the tops of the saw teeth to the same level. Second is a pin gauge for setting the height of the raker teeth when peening over the hook. Lastly is another height gauge for finish filing the rakers to a consistent height, accurate to the thousandth of an inch. The tool at the bottom left is the setting spider, the subject of today’s post. How about some instructions?

Simmons Saw Sharpening Guide

And learn from the master filer I learned from, a fantastic set of videos that include a bit of hammer straightening of saws.

The spider is used as a gauge to accurately determine the degree of set in each tooth. Simple and brilliant, it immediately struck me that such a tool could be easily made and used on maebiki-oga.


You’ll catch this if you watch through the videos above, but basically the spider has a small difference in height between the long arms. Placed on the saw you see how it rocks back and forth. If the long arms rock the tooth needs more set, if the short arms rock the tooth is over set. Its important to note that this tool only works if the plate of the saw is quite straight, flat, and even of thickness.


I started by cutting a cross out of some mild steel a bit thicker than 1/8″.


I stuck it in a vise to bend the edges over, filed a flat land on all the feet, and leveled them to the same height on my diamond stone.


Then one leg could be lowered by grinding with part of the spider off the stone, checking how much material had been removed with a feeler gauge.  For the large cross cut saw the spider was set at about .012″, for my maebiki-oga I adjusted the spider to gauge .010″ of set, which with a plate thickness of .085″ gives me a kerf just under 1/8″.


Luckily the plate on my saw is pretty consistent and flat, so I got right to work checking my set. Up to this point I’ve been setting by eye by sighting along the plate held flat. If you have an oga saw with a rough hammered surface you’ll have to depend upon setting by eye. I still don’t completely trust the spider, but it is a great analytical tool to gauge how well I’m setting, and weather I’m actually seeing the degree of set correctly. As it turns out, I had over set one side and under set the other, probably due to the change in orientation of the saw when flipping it to peen the teeth over.


For setting teeth you need a small anvil, mild steel is okay, as long as it has a rounded edge that allows the tooth to make contact in the right spot. The teeth of a whale noko are hard enough that if you were to strike the tooth while unsupported you run the risk of breaking it.


With the plate held in your lap at a lowered angle to the flat  you can place the tooth line on the anvil and strike the upper third of the tooth.


I’m using a new hammer for setting, a cross peen with a ‘v’ shaped edge, not rounded, that is basically a large single edge version of a Japanese setting hammer. If you use too light of a hammer you find yourself whacking the tooth with a rather random amount of force. Adjusting the set within a thousandth of an inch requires control. Also, bending teeth back that have been over set on such hard steel is not an option, they just break off, so get it right or you’re stuck with an over set tooth until you sharpen it down a bit.

Happy sawing! I hope more people now are getting these big saws ready for the cut and avoiding the hassle of a chain-saw.

Practicing Hizumi: Hammering saws flat

Most woodworkers that are interested in hand tools manage to collect a fair number of saws that have seen better days…That’s a polite way to say they were beaten the hell out of, bound in a cut and bent, kinked, or otherwise mangled. A bent saw will give no end of trouble when sawing, basically relegating it to a wall ornament. That is, unless a little love and care can straighten them out.

Rather counter intuitively the best way to remove distortion from a saw is beating on it with a hammer, the process that is known in Japanese as Hizumi. Apparently hizumi also refers to working the kinks out of peoples backs and body, should give you some idea that this is analogous to massage. Hizumi is used in almost all of the blacksmithing trades dealing with tools, from knives to chisels and kanna, all require a bit of straightening after rough forging and tempering before the final work can be done profitably at the grinding stone. With saws metate take the art of hizumi to a whole different level, as a saw often comes out of hardening shaped like a potato chip.

One of the biggest reasons I endeavored to make my way to Vermont and Mark Grable has been to study hizumi, as I have no shortage of saws that need straightening, and metate is close to becoming a forgotten skill in this age of power everything and disposable blade culture.  Of course, you know better, otherwise you wouldn’t be reading this blog. So where to start?


How about cleaning up that rusticle you just found in grandpa’s old barn or on ebay? Mark’s approach is to use 40 grit sand paper and a tool made by Yataiki that lets you apply a lot of pressure and control as you work off the rust.


It consists of a sen like handle with a piece of bicycle tire nailed on to grip the sand paper. Simple and effective. The point here is not to sand out all of the pitting and restore the tool to a bare metal fine finish, merely to render it free of rust and to a point where the saw plate can be viewed well in the correct light condition.


So, take one potato chip…I mean saw blade and sit back in some indirect diffuse light and get the shape of the saw in your head. The whole shape of the saw, its not enough to merely notice a bump here or there. The thing about distortions in a saw is that they have a habit of relating to each other, a certain balance of forces and tension that is effected in the saw as a whole. Attempt to remove one problem and you might just make another worse.

Its better to start on thicker western style saws, and better yet to practice on stuff like the above photo of an old circular saw blade that’s been annealed (a bit over annealed, I’d say).

Flex the saw lengthwise between your hands and listen for the dreaded nuki, poka-poka, or oil-canning. That consists of a section of over tensioned metal that wants to pop back and forth in its unrequited state of inbalance with the rest of saw plate. If that’s apparent you need to put the saw away and not work on it until you have quite a bit more experience, but at least its a problem that can be dealt with. Just today somebody sent Mark a ryoba saw with the worst twist and nuki I’ve ever seen in a saw, and Mark got right to work hammering that shit out, not that I could tell exactly how he went about it.

The first tool you’ll employ looking at the saw’s condition is a straight edge, with the saw held up to the light in such a way that you can see the line of light between the saw and the straight edge. First look along the width of the saw on both sides, then both directions diagonally, and finally along the length of the saw. Remember, you’re trying to get in your minds eye the total shape of the saw, not merely a localized spot or two.

Next you look at the saw along its width and length at a low angle to the incoming light. Its hard to describe what the right angle is like, but you’ll know it when you start picking up the surface topography of the saw. A cold beer is appropriate at this stage as you contemplate the saw and your local universe, the birds and the mountains, and the wind rippling the pond. If its late in the evening you put the saw down and go enjoy the sunset, maybe practice some calligraphy, hew a beam, or get stoned and enjoy the company of your friends.


Back in the shop the saw awaits and the anvils and hammers are positioned. In the Japanese tradition you work seated, maybe with the anvil tilted to return the light to your eye at the right angle to allow you to see your hammer strikes on the lightly oiled surface of the plate.


Hammers for major distortion are any heavy round faced hammer at hand. More refined and focused work involves a cross-peen hammer.

The hammer strikes the high spots, with the cross peen edge perpendicular to the length of the bow. Try to connect areas of distortion, and notice how working on one spot effects the others. Work both sides of the saw, an absolute necessity with removing twist that consists of concave bows that oppose each other diagonally. Strike blows hard enough to remove half of the distortion, and then half again, and so forth.

Flex the saw constantly to check for the pop of oil-canning, which can happen from working one spot too intensively. If you catch it early its much easier to remove.

A word on nuki. I don’t know enough at this point to give any advice should you find yourself with a saw that has this problem, but from what I’ve seen it involves working the periphery of the nuki on both sides of the saw, evening the tension and pulling it into the rest of the saw with a large round faced hammer.


At first, to put it bluntly, I was beating the hell out of this saw blade, and left a pretty crappy surface as a result.


But it is a lot straighter, no? If you just read this whole blog post and realized I didn’t really tell you how to straighten your saw, good point. Its not so simple as a prescription for hit here and the problem will be solved. If I can say one thing it is this, something Mark told me when I first arrived in Vermont, know when to stop.