The Matsui Precision Notched Straightedge

Matsui Precision Bevel-edged Straightedge with notch

You cannot teach a crab to walk straight.


This post is about a tool that looks quite ordinary but is in fact extraordinary in subtle ways.

Why Do Woodworkers Need a Good Straightedge?

When woodworking we need to be able to mark and measure straight lines and examine the precision of edges and surfaces. There are several ways and tools available to accomplish these tasks, but the steel straightedge is efficient for shorter distances, assuming one’s straightedge is up to the job.

For most woodworking tasks we don’t need a precision straightedge. But for those few activities where it is necessary, nothing can take its place. So what are some of those activities? I can suggest a few from my experience:

  1. I use a precision straightedge as a “Standard” to check that my working straightedges and squares (the ones that are used and abused daily) are truly straight and square. This is necessary because, during use, Murphy governs all operations, while pernicious Iron Pixies dance among the piles of dandruff on his shoulders. Due to their malicious ministrations, measuring and marking tools are easily damaged, wear-out, and lose tolerance so I need a reliable “Standard” to check them against regularly. Of course, you can’t check for straight or square unless you have a truly straight line/surface to index from. It would be silly to imagine that the edge of one’s tablesaw top or jointer table are perfectly straight without first checking it against a reliable standard;
  2. I use a precision straightedge to examine the soles of my handplanes to help me keep them straight, flat and free of wind because it’s very difficult to plane a flat surface with a screwy plane. No matter how much time I invest in truing my planes, I’ve found the results are never better than the straightedge used.
  3. Check that lapping plates and the float-glass plate I use for truing stones and plane soles remain within tolerances. Yes, they wear out too.
  4. Check that the tables of stationary equipment such as tablesaws, bandsaws, jointers, and planers are true, and that infeed/outfeed soles of handheld electrical planers are properly aligned;
  5. Check that surfaces of wooden components of special projects requiring extra precision are true.

Do you ever need to accomplish any of these tasks?

Tasks for Which the Matsui Precision Straightedge is Not Ideally Suited

The Matsui Precision Straightedge is not an expensive tool, but since it is one I rely on, it is most cost-effective to protect it from premature wear and damage, so the following are tasks for which I use a less-expensive and less-protected “working straightedge” instead of my Matsui precision straightedge:

  1. I don’t use it for checking sharpening stones. The Matsui straightedge can do this job with style, but after a few years of being pressed against (and dragged over) abrasive stones, the tool’s precision would be degraded. Better to use a less-expensive straightedge for this job, and check it occasionally against the Matsui Precision Straightedge to confirm it’s still straight. If it isn’t, fix or replace it.
  2. I don’t use it for daily general woodworking tasks. Once again, the Matsui straightedge can do general jobs with style, but after a few years of being pressed against (and dragged over) wooden surfaces, the tool’s precision would become degraded prematurely. Instead I use a “working straightedge” that has been checked against my “Standard” Matsui Precision straightedge;

How To Use a Precision Straightedge for Checking Tools and Surfaces

Neither the human hand nor eye can measure a straight line or a true plane with any precision unaided, but there is one technique older than the pyramids all woodworkers must be proficient at, namely to place a truly straight, simple straightedge on-edge on a surface to be checked, be it a board, a jointer outfeed table, or the sole of a plane, and shine a light source at the gap between the straightedge and the surface being examined. If gaps exist, light will pass between the edge of the straightedge and the surface being checked confirming the surface is not straight and/or flat. The human eye can detect even a small amount of light this way and both quickly and effectively judge how flat the surface being checked is with a surprising degree of accuracy.

Feeler Gauge

Another technique that yields more precise values without relying on Mark1 Eyeball is to place the straightedge’s beveled edge against the surface to be checked, and insert feeler gauges into gaps between the straightedge and the surface. If the feeler gauge selected won’t fit, then one replaces it with thinner gauges until one that just fits is found.

Once you know the value of the gap between your straightedge and the area of the board you need to true, for instance, you can divide the measured thickness of the shaving your planes takes in a single pass (easily checked with a vernier caliper) to calculate how many passes it will take to true the high-spots on a board. eliminating a lot of the guesswork that makes precise woodworking difficult at times.

To reliably perform these checks, we need a truly straight straightedge. Straight is a relative thing, but straightedges sold for woodworking are seldom straight because purveyors rely on purchasers to not bother, or even know how, to check the quality and precision of the straightedges they sell.

Another reason honest, precision straightedges are relatively rare among woodworking tools is that making a high-tolerance piece of hardened steel that is straight, and will stay that way, is hard work that most woodworkers are neither inclined to appreciate nor bother to check, much less pay for. Is ignorance bliss? I believe it is in the natures of our Gentle Readers to always strive to improve the quality and efficiency of their work. A high-quality precision straightedge is an essential tool in that blissful quest.

Challenges & Solutions

The dilemma of the straightedge is that it must be thick and rigid enough to prevent warping and flopping around in-use, but reasonably lightweight and not too bulky or it will be clumsy. At the same time, it must not be too thick, or it will block out most of the light passing between its edge and work-piece making it useless.

Another challenge the straightedge faces is the constant threat of damage. If the delicate edge is too soft, it will become dinged and deformed instantly becoming inaccurate. And if the straightedge rusts (the bane of steel since ancient times), precision will suffer.

What are the viable solutions? They are obvious and proven, but seldom implemented well. Here is how Matsui Precision does it.

Stainless Steel Construction

First, they use high-quality stainless steel to prevent corrosion. If you work in humid conditions or if you will admit to perspiring salt-laden moisture at times, then this is important, but not rare.

Properly-sized, Precision-ground & Polished

This straightedge is not an insignificant piece of stainless steel. It is available in various lengths, but in the case of the Matsui’s 400mm straightedge (a handy, reasonably-priced length), the blade is 34mm wide and 3mm thick, enough to keep the blade rigid in use and prevent warping, but not so wide or thick as to feel heavy or clumsy. It weighs 320gm, a nice balance of rigidity and weight.

Compact, lightweight tools made using quality materials efficiently have a deep genetic attraction to the Japanese people.

What is more rare is the fact that Matsui then precision-grinds and precision polishes the stainless steel (not the same thing) so the tool is as straight and flat as machinists require, because this is a tool designed to the higher standards of machinists, not just woodworkers.

Hardened & Trued

Matsui also hardens the stainless steel to ensure the tool is rigid and will resist wear and damage over its long useful lifespan.

During heat treating and grinding the metal warps slightly. After stress-relieving the tool, Matsui inspects each tool one-by-one and corrects irregularities or rejects those that cannot be sufficiently corrected. It’s called quality control, something that never happens in China or India in the case of tools intended for woodworkers.

Beveled Edge

To make it easy to see light passing between the straightedge and surface being checked, one edge is beveled. The importance of this detail cannot be overstated.

The Notch

The Matsui Precision Straightedge being used to check the sole of a 70mm finish handplane with a blade by Sekikawa-san. The notch fits over the cutting edge so one can check the sole with the blade protruding as it will be in-use. In this photo the blade has been extended waaay too far out of the mouth to make it easy to see the cutting edge. Please notice the light showing between the straightedge and the sole indicating that something is not right. The wedging pressure of forcing the blade to project this ridiculous amount has warped the block so that the most important part of the sole, the area directly in front of the mouth, is not touching. The point is that the notch makes it possible to check the sole with the blade projecting the intended distance, a job simply not possible with an ordinary straightedge.

In the case of the tool we are introducing here, Matsui cuts a small semi-circular notch in the beveled edge of the blade to provide clearance for irregularities in the surface being checked, such as welds, or in the case of woodworking tools the cutting edges of the blades of handplanes, electrical planers and electrical jointers. This is an important and unique feature.

Why is this notch so useful? The problem with using a metal straightedge to check/true the sole of a handplane has always been that, in order to correctly check for flatness/wind, the blade must be set to project from the plane’s mouth the same amount it should be when the plane is being used, because in the case of Japanese planes the wedge-shaped blade applies slightly different pressures on the wooden block at different depths in the block, producing variable degrees of deflection.

But if the blade is projecting from the mouth from the same amount as it will be in use, then the straightedge will ride on top of the blade preventing a proper examination, and at the same time, possibly dulling the blade and gouging the straightedge. The solution has always been to adjust the blade to not actually project, but to be just in-line with the sole, a fiddly process that has resulted in many dulled blades, scratched straightedges, and inaccurate examinations.

With the elegant Matsui Precision straightedge, however, the notch fits directly over the projecting blade avoiding the irritating and time-wasting fiddling normally required to get the blade in the exact position, one that ultimately yields an imperfect reading.

If you need to maintain handplanes, electrical woodworking tools, or do precision woodworking and need an accurate, reliable, lightweight, durable, reasonably-priced straightedge to help take the guesswork out of these jobs, this product is just what you need. I have been using one for years and couldn’t get by without it.

If you are interested, send us a message using the form below.


Matsui Seimitsu Precision Squares

Maestro Bruno Walter 1876~1962

By concentrating on precision, one arrives at technique, but by concentrating on technique one does not arrive at precision.

Bruno Walter

We would like to introduce some excellent tools made by a company called Matsui Seimitsu Kogyo located in the city of Sanjo in Niigata Prefecture in Japan. We have been using this company’s products for many years and have started carrying a few by popular demand. The time has come to share these with our Beloved Customers in general.

Matsui Seimitsu Kogyo translates to “Matsui Precision Industries,” but I’m just going to call them Matsui Precision. The company has been around for over 100 years. They may not be the largest manufacturer of precision tools in Japan, but their reputation is unsurpassed.

Allow me to digress for a moment while I grind these oak galls to make some ink. Just about out, you see. Anyway, as you can probably tell from my posts to this blog so far, and which will become even more obvious in the future, I love ancient tools and learning how beautiful work was done by determined people using basic, even crude tools. But I am also fond of excellent refined handtools that help me do a better job more efficiently. I am always on the lookout for such tools, and this post is about one such tool I discovered. One thing I like about this tool is that while it is essentially unchanged from the days when Noah was knee-high to a grasshopper, Matsui Precision has subtly improved the ancient and lowly square in ways that are not immediately obvious. For one thing, it really is a “Precision Tool,” even though you wouldn’t think so just by looking at it.

The idea of using “precision tools” for woodworking is offensive to some. I have seen online discussions about using precision tools for woodworking induce psychotic events in some amateur woodworkers. Perhaps the very thought of such tools triggers hallucinations of digital micrometers swooping through their dreams while pissing down on the eternal beauty flowing from their masterful hands. Or perhaps they imagine the smelly poor-quality Chinese-made tools they buy in bundles from Harbor Freight to be more expressive of their artistic intentions than the cold precision tools of the sort less artistic machinists use. To the former I say “Don’t drink alcohol with your medications.” To the latter I exhort: “Extract your head from your nether regions and behold the light of civilization!” 

Anyway, that’s enough ink to last a month, so enough free psychoanalysis. Let’s get back to Matsui Precision Squares.

They have six distinct advantages over almost any other simple square you will find:

  1. Precision: Unlike any square ordinarily available to woodworkers, these are manufactured and certified in accordance with Japan Industrial Standards (JIS). The relevant standard is JIS B7516 (2005). The hardened steel model (SY Series) is rated Grade 1, and the graduated model SM Series) is rated Grade 2. Accordingly, these squares precisely measure 90°. Without using other precision instruments the only way to confirm this claim is with another high-precision machinist’s or diemaker’s square. The MP square will pass this test, not to woodworking tolerance, but to machinist’s tolerances. We guarantee it.
  2. Lightweight and Handy: You will not find a precision square lighter or handier. The blade (long leg) and stock (short leg) are relatively thin, light in weight, and handy to use, unlike machinist’s squares and combination squares with their thick, heavy, clumsy, flat stocks and blades which make it difficult to see light showing between them and the workpiece. The Matsui blade is relatively thin making the square easy to use for woodworking.
  3. Durable: The stock and blade of both SY and SM series tools are joined by spot welds, unlike all but the most expensive machinists squares; Not a compression joint, not glued, not bolted, not pinned. They are not indestructible, of course, but the stock or blade will bend or melt before this connection fails.
  4. Corrosion-Resistant: both blade and stock are stainless steel so they won’t rust even if used and stored in constantly humid conditions, even if you have sweaty hands.
  5. Hardened: This feature is most important in my opinion. The blade and stock of the SY series squares are hardened, a very unusual feature. For the woodworker, this means that the blade will better endure the scraping and shaving action of steel scribes and heat-treated marking knives used in layout, and will stay straighter much longer than all but the most expensive machinist’s and diemaker’s squares.
  6. Relief Cut: The stock has a small half-circle notch cut into where it meets the blade to prevent wood shavings etc. from jamming between the blade and/or stock preventing them from making clean contact with the workpiece ruining accuracy, an important detail indeed.

In short, the Matsui Precision square will help you do better woodworking, easier, and for many years.

We carry two models of Matsui Precision squares. The first is the SY Series pictured below, with a hardened stainless steel blade but without graduations. The stock is hardened to Rc54~57 and the blade to Rc48~52. This is the tool we use and recommend for layout using a marking knife.

The SM series is different from the SY Series in three ways, reflected in the lower price. First, the blade is not hardened. Second, it has deeply etched graduations (not laser etching) which are perfect for using with a scribe or marking knife because the tool’s tip can get into the graduation for positive indexing. And third, the level of precision is one level lower at JIS Grade 2. The graduations include a √2 scale useful for determining the diagonal distance of a square by measuring a side.

If you are tired of squares that aren’t square, that are bulky, heavy, and clumsy to use, that are destroyed by a single drop, or that get eaten alive by your marking knife or scribe, then you should give these a try. You’ll never look back.

If you would like to purchase one, please inquire using the form below.

Matsui Precision Hardened Stainless Steel Squares (w/o graduations) Model SY-15
Product IDNominal Size (mm)Blade lStock lStock t¥ Price
Matsui Precision Hardened Stainless Steel Squares (w/o graduations)
Matsui Precision Stainless Steel Square (w/o graduations) Model SM-10
Product IDNominal Size (mm)Blade lStock lStock t¥ Price
Matsui Precision Stainless Steel Squares (w/ graduations)

If you have questions or would like to learn more about our tools, please use the questions form located immediately below. Please share your insights and comments with everyone in the form located further below labeled “Leave a Reply.” We aren’t evil Google or incompetent facebook and so won’t sell, share, or conveniently and profitably “misplace” your information.