The Varieties of Japanese Chisels Part 16 – High-speed Steel Atsunomi

I am past scorching; not easily can’st thou scorch a scar.”

Herman Melville, Moby-Dick or, the Whale

Your humble servant has previously presented 15 varieties of Japanese chisels for Gentle Reader’s kind consideration in this series so far. In this article we will examine a specialized version of the Atsunomi previously presented in Part 8 of this series, one made from high-speed steel.

The C&S Tools High-speed Steel Atsunomi

The chisel in question is made by Mr. Usui Yoshio of Yoita-cho, Nagaoka City, Niigata Prefecture, under his brand name of Sukemaru. The shape of this tool is identical to his standard atsunomi, the only significant differences being the type of steel used and the bright appearance of the blade.

This is not a small chisel but a professional-grade, rugged tool with an overall length of approximately 300mm (12″). It is an indispensable tool in some situations.

If you need a smaller, handier, and more economical HSS chisel, please take a look at our HSS Oiirenomi also by Sukemaru.

What is High-speed Steel?

So just what is high-speed steel (HSS)?

HSS is a tool steel developed for manufacturing commercial cutters, dies, etc. In this case, Usui-san uses a high-speed steel designated SKH51 in Japan, the equivalent to M2 in the USA, BM2 in the UK, HS6-5-2 in Germany, and Z85WDCV06-05-04-02 in France. This is the most popular HSS formula in the world. If you own router bits without carbide cutters, and not made in China, you own this steel.

This variety of HSS contains buckets-full of tungsten, molybdenum and chrome, with a stout vanadium chaser.

After oven heat-treat, these chemicals make the steel tougher, more abrasion-resistant, and more resistant to softening (aka “temper-loss”) when subjected to high-temperatures than regular high-carbon steel. Its nickname of high-speed steel comes from the tendency of cutters made from this steel to retain their hardness even when worked so hard blade temperatures become hot enough to draw the temper of standard steel cutters, softening and making them useless.

The chemical composition is listed below, just in case you are interested. You can see what I mean about “buckets.”

Chemical composition of SKH51/M2 HSS Steel

Why Use High-speed Steel?

No doubt a question jumping up and down and screaming in Gentle Reader’s mind at this point is “what are the properties of high-speed steel and what difficulties can a chisel made from this special steel help me overcome?”

Toughness and Shock Resistance

Perhaps the most significant property of high-speed steel is its toughness. SKH51 (M2) steel is the most shock-resistant of the high-speed steels, making it especially suitable for use in a chisel that may impact hard objects in daily use but must survive without chipping or breaking. This toughness provides huge benefits in the situations described further below.

Abrasion Resistance

Abrasion resistance goes hand-in-hand with toughness, but it is a different characteristic many misunderstand. It does not mean a cutting edge will be sharper than a cutter made of high-carbon steel, only that it won’t wear and become dramatically rounded-over as quickly. In the case of chisels, a blade made from highly abrasion-resistant tool steel will reach a certain level of sharpness (or dullness) and remain at that level a relatively longer time allowing a cutter to keep on cutting without becoming useless. But the quality of the cut will decrease, and energy necessary to motivate the blade will of course increase as the blade dulls. No free lunch, sorry to say.

Abrasion resistance is not typically considered overly important in blades where great sharpness is high-priority, but it is extremely important when the blade is used to cut materials such as exotic hardwoods that contain silica crystals, or Engineered Wood Products that contain hard adhesives and/or highly-abrasive particles such as silicon carbide deposited by sandpaper, or dirty wood contaminated with sand, grit and other contaminants that will literally destroy the cutting edge of a plain high-carbon steel blade making it useless.

Just as a low-revving high-torque truck would be at a hopeless disadvantage in a Formula One race, a screaming McLaren MP4/6 with all its speed, power and agility couldn’t tow a heavy trailer 100 yards through the mountains. Horses for courses.

Engineered Wood Products

One major challenge the HSS atsunomi excels at overcoming is modern wood products called Engineered Wood Products (EWP)

Commercial carpenters and cabinet makers nowadays have no choice but to use modern EWP such as plywood, MDF, HDF, OSB, LVL, glulams, etc.. Unlike new, clean, solid lumber cut with saws and planed with knives to final dimensions, engineered wood products are comprised of wood veneer, chipped wood and/or sawdust glued together by hard adhesives that will harm standard steel tool blades. HSS handles these difficult adhesives easily.

A bigger problem associated with EWP is the extremely hard abrasive particles left embedded in them by the sanding belts used to dimension and smooth them, particles much harder than any heat-treated steel, and that will quickly destroy a good high-carbon steel chisel. Being much tougher and more abrasion resistant than high-carbon steel, HSS can handle this abrasive residue without being destroyed. That does not mean abrasive particles do not scratch and dull HSS atsunomi cutting edges; After all, silica carbide particles are harder than high-speed steel. It just means HSS blades won’t chip or break and will keep on cutting longer than HC steel blades.

Restoration & Remodeling Work

Another type of work this HSS atsunomi excels at is restoration work, remodeling work, and chisel work around concrete and masonry.

In the case of restoration work, the job usually involves cutting wooden structural members and finish materials that are old and dirty and contain hard abrasive dirt, sand, small stones and of course hidden nails and screws that will not only dull a chisel blade but may badly chip it. 

For instance, a Beloved Customer who is a timber-frame carpenter in the Czech Republic was tasked with splicing segments of new timber to replace rotted-out sections of a large number of 300 year-old rafters during the ongoing restoration of the Grand Priory Palace located in Prague (constructed from 1726 to 1731), an ancient city with many beautiful, old structures.

Grand Priory Prague
Grand Priory Prague
Grand Priory Prague Roof Frame Restoration
Grand Priory Prague Roof Frame Restoration

The wood was dirty and full of gravel and broken-off nails that chowed down on standard chisels without even pausing for a drop o’ Tabasco Sauce. But our HSS atsunomi chisel made it possible for him to cut and fit the timber splices while working on the steeply-slanted roof far above cobble-stone streets without chipping the blade and without stopping the work for frequent resharpenings beyond an occasional touchup with a belt sander.

In the case of remodeling work, one must routinely cut precise holes through existing wood contaminated with abrasive dirt and hiding screws and nails, as well as lathe, plaster and drywall containing abrasive sand, and in close proximity to mortar and concrete which contains sand and gravel aggregates that will dull, chip and even destroy a standard chisel in two shakes of a lamb’s tail. 

If you have ever done remodeling work or an installation requiring chiselwork, you know the despair one feels when gazing upon the damage done to a beloved tool.

Likewise, during installations, cabinetmakers must make precision cuts in abrasive engineered wood products such as plywood, OSB and MDF. Our HSS atsunomi chisel, as well as our HSS oiirenomi chisel excel at this job being far more durable than standard chisels with high-carbon steel blades.


The jigane Usui-san uses for his HSS Atsunomi is a harder version of the standard low-carbon steel he uses for his standard atsunomi. It is not stainless steel, however, and can corrode.

Likewise, the furniture (katsura (hoop) and kuchigane (ferrule)) are made from mild steel, not stainless steel, despite the bright appearance, and will exhibit corrosion over time. As an option, these two parts can be ordered blackened creating a two-toned chisel some people find attractive.

Heat-treat and Hardness

To prevent chipping, the HSS blade is heat-treated in a special computer-controlled oven following a specific temp/time curve to achieve a hardness of Rc63, intentionally a little softer than the maximum hardness of Rc64 listed for this steel. Even then, this is harder than nearly all currently-produced Western chisels we are aware of. 

The blade’s bevel angle is 30°, the standard angle for Japanese woodworking chisels. To reduce denting you may want to increase the angle to 35° if you will be cutting through hard materials.

Resharpening in the Field

Another huge advantage of Sukemaru’s HSS chisels is that they can be quickly resharpened to a usable cutting edge in the field using angle grinders and belt sanders without losing temper and softening so long as one is careful to keep temperatures below 650°C (1200°F), not difficult to do if one pays attention. Don’t underestimate the efficiency this feature will bring to your work some days.

The compromise with HSS chisels is that, while they can be made extremely sharp using stones and proper technique, they will never become as sharp as our hand-forged high-carbon steel chisels. Moreover, they will take twice as long to sharpen by hand using conventional wetstones and waterstones.

Sharpening time can be reduced dramatically by using aggressive diamond plates or diamond stones.

We have personally tested these chisels to failure and resharpened them. We are confident of their quality and performance.

If you need an exceptionally tough chisel that can “take a lickin and keep on tickin” even in conditions that would utterly destroy a regular chisel, then the HSS Atsunomi, or where a smaller tool is required, its tough little sister the HSS Oiirenomi, will get the job done for you.

If you would like to know more about these chisels, please drop a note in the form below titled “Contact Us.”


If you have questions or would like to learn more about our tools, please click the see the “Pricelist” link here or at the top of the page and use the “Contact Us” form located immediately below.

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4 thoughts on “The Varieties of Japanese Chisels Part 16 – High-speed Steel Atsunomi

  1. I have a set of 4 of these. They are indispensable when I’m restoring or repairing old boats. Lots of hidden nails and sometimes screws that will ruin a carbon steel atsu-nomi.


  2. Great article! I also use these regularly for job site work. Very useful when you are doing some reclaimed timber and end up wrecking your edge on some hidden metal inclusion – simply grind out the dent and resume work! No worries about destroying the temper on these guys. However this brings me to a question I have had for some time:

    You mention that the “temper loss” of HSS chisels would occur around 650*C. What would the typical “softening temperature” / “temper-loss” temperature be for standard Japanese high carbon steels. I imagine this temperature would vary some from one blacksmith’s work to another’s as there is inconsistencies in forging methods (i.e. some are more ‘cold’ forged than others. The great and famous Tokyo smiths (Ichihiro, Kiyotada, etc) feature incredibly hard steels and thus are products of a ‘cold forging’ process, correct? From what I have been told, they were potentially tempered at as low as 100*C? At 100*C I would imagine that it would be quite easy to kill the temper on your tool. Please correct me if I’m wrong, but this would mean boiling water would be enough to kill the temper in the case of a ‘cold forged’ Ichihiro.

    Appreciate your input!


    1. Jay T: Thanks for visiting the Blog! Happy New Year! As I understand it loss of temper can indeed begin at around 100C˚ in plain HC steel, but one needs to go much higher for efficient results. This means that if the steel becomes too hot to touch with bare skin, the temper is at risk, so 100˚C, the boiling temp of water at sea level, can soften steel given time. I have heard old carpenters say that a brittle saw or chisel could be tamed by exposing the tool on a hot tin roof on a summer’s day. A candle flame alone is adequate to soften steel in small areas.

      But I don’t know the temps Ichihiro or Kiyotada used. I have heard from reliable sources that neither of them got good results for a long time, but after much experimentation they got the combination right. That was one advantage of being a member of the Tokyo Chisel Smith Guild

      Please check out this PDF from Hitachi Metals about their steels. The first metal in the top row is Shirogami No.1. The Quench temp shows is 760~800˚C and the tempering temp is 180~220˚C. The hardness is 60+ Rc.

      This article by Niigata Prefecture’s research center shows some interesting details. The steel tested is Aogami No.2 (Row 6 in the Hitachi pdf). It has added chrome and tungsten to reduce warping and widen the range of quenching temperatures. They heat treated samples and showed the results for 7 of them. In each case, the quench temp varied from 750˚~900˚C (1382˚~1652˚F) in water, but the tempering temp was 180˚C (356˚F) in air for one hour. Figure 4 at 775˚C (1427˚F) shows the best, finest, most uniform crystalline (Austentite) structure. Lower temps are not as good. Higher temps are worse. 25˚ one way or the other makes a big difference. And remember this is Aogami 1, which is much less sensitive to variations in temp than Shiro 1. I hope this answered your question, but I doubt it.


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