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

We have presented 15 varieties of Japanese chisels for your consideration at this blog to-date. In this post we will examine a specialized version of the Atsunomi previously presented in Part 8 of this series, 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 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, 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.”

CMNSiCrWMoV
0.85%0.28%0.30%4.15%6.15%5.00%1.85%
Chemical composition of SKH51/M2 HSS Steel

Why Use High-speed Steel?

The next question in our Gentle Reader’s minds, no doubt, is “what are the properties of high-speed steel and what difficulties can a chisel made from this special steel help me overcome?” Let’s answer these questions below.

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 long 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 with use.

Abrasion resistance is not typically considered overly important in blades where great sharpness is given 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 strong truck would be at a hopeless disadvantage in a Formula One race, a 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, 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, it just means they 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.

The wood was dirty and full of gravel and broken-off nails that chowed down on standard chisels without 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 that took a chiselwork to perform, 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.

Jigane

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. 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 oven in accordance with a formula to a hardness of Rc63, intentionally a little softer than the Rc64 hardness listed for this steel. Even then, this is harder than nearly all currently-available 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. They are not ideal for all jobs.

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

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 destroy a regular chisel, then the HSS Atsunomi, or where a smaller tool is required, its tough little brother 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.”

YMHOS

If you have questions or would like to learn more about our tools, please use the “Contact Us” 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, incompetent facebook, or troublesome Twitter and so won’t sell, share, or profitably “misplace” your information. May a thousand bot flies make a home in my eyebrows if I lie.

Links to Other Posts in this Series

2 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.

    Like

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