The Varieties of Japanese Chisels Part 5 – High-Speed Steel Oiirenomi (HSS 追入鑿)

Sukemaru High-speed Steel Oiirenomi

“Life is not a matter of holding good cards, but of playing a poor hand well.” – Robert Louis Stevenson

So, you finished building that fine cabinet, or 8-panel entry door, or carved balustrade and the day has come to install it at the jobsite. Will you need to cut a bit of gypboard or lath-and-plaster while installing it? Might your chisel get jammed against or into bricks or concrete in the process? Will you need to cut a notch in sandpaper-grit filled plywood or OSB? Any hidden screws or nails in the way that might require more than stern words?

Jobsite installations and remodeling often demand work everyday tools can’t accomplish without being serious damaged. At that moment, having a tool tougher than the job is the difference between working and whining. This is that tool.

DESCRIPTION

HSS oiirenomi are a modern variation of mentori oiirenomi made using high-alloy steels tougher and more resistant to abrasion and high temperatures than more traditional steels.

These chisels are useful for doing remodeling work and cabinet and equipment installations where plywood, MDF, OSB, LVL, drywall, acoustic board, insulated board, plaster, mortar, underlayment and studs full of hidden nails, and even ALC (autoclaved lightweight concrete) panels need to be cut, trimmed, fitted or demolished. Demolition…Oh joy (not).

What is High-speed Steel?

So just what is high-speed steel (HSS), and why bother with it?

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 HSS?

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 and grit. 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 Oiirenomi excels at overcoming is working 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, glu-lams, 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 Oiirenomo 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 400 year-old rafters in a restoration project located in Budapest, 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 this Beloved Customer’s set of our HSS Atsunomi chisels (identical to the HSS Oiirenomi chisels which are the subject of this article only much bigger at 300 (12″) overall length) made it possible for him to cut and fit the timber splices while working on the steeply-slanted roof four-stories above a cobble-stone road without chipping the blade and without frequent resharpenings, as professional timber framing work frequently demands. 

Oiirenomi are much handier than Atsunomi, for remodeling work and installation work, a job that requires one to 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 Oiirenomi are far more durable than standard chisels with high-carbon steel blades for these jobs.

Jigane

The jigane Usui-san uses for his HSS Oiirenomi is a harder version of the standard low-carbon steel he uses for his other chisels. 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 prescribed 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. You may want to increase the angle to 35° if you will be routinely cutting through hard materials to reduce denting.

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 edge 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.

Before I tried my first HSS oiirenomi, I kept a couple of old plastic-handled steel-cap Stanley chisels in my toolkit as “beaters” for cutting gritty, abrasive materials. They were soft and instantly dulled, but their edges would dent instead of chipping and were easily repaired. Poor things; some days they ended up looking more like rounded-over wide-blade screwdrivers than wood chisels. HSS chisels are just the ticket for this kind of brutal work.

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

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

A 10-pc set of Sukemaru’s HSS Oiirenomi with Japanese Red Oak handles in a presentation box.

Standard widths for high-speed steel oiirenomi are 3mm, 6mm, 9mm, 12mm, 15mm, 18mm, 21mm, 24mm, 30mm, 36mm, and 42mm.

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

YMHOS

Links to Other Posts in this Series

If you have private 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.” Your information will remain confidential (we’re not evil Google or incompetent facebook).


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