The Varieties of Japanese Chisels Part 4 – Kakuuchi Oiirenomi (角打追入鑿)

Kakuuchi Oiirenomi by Hidari no Ichihiro (Hyotan mark)

“Do not wait; the time will never be “just right.” Start where you stand, and work with whatever tools you may have at your command, and better tools will be found as you go along.”

George Herbert

The oldest style of oiirenomi currently available nowadays is called ” kakuuchi oiirenomi” (角打追い入れ鑿)which means ”square-forged oiirenomi,” refering to the squarish shape. In cross section, the blade is rectangular with 4 more-or-less square outside corners. Other than this cross-sectional detail, it is identical in appearance to the mentori oiirenomi we discussed in my earlier post here.

DESCRIPTION

Where the Shinogi Oiirenomi in the previous post is thin and light, the Kakuuchi Oiirenomi is bulkier and heavier. They are also stiffer in the blade and even in the neck, which can be an advantage in narrower widths.

This added stiffness is not due to the extra mass of metal alone, but also to the fact that the steel layer is wrapped further up the blade’s sides than is possible for the thinner beveled sides of the mentori oiirenomi, as you can see in the photos above. Wrapping the high-carbon steel cutting layer up the blade’s softer low-carbon steel sides in this way creates in effect a hardened steel “U” channel with an increased moment of inertia, which makes the blade much stiffer. The thicker the chisel’s sides, and the deeper the U channel, the stiffer the blade will be.

The U-channel construction of Japanese chisels is a clever but subtle structural detail unique in the universe of chisels and one most people are not aware of.

Carving chisels do not have this U-channel detail and therefore are not as stiff or as tough as chisels that do. When you are considering buying a chisel, this is an important feature to confirm.

This style of chisel is better suited to cutting mortises than mentori oiirenomi (beveled oiirenomi), not simply because they are stronger, but because the squarer side edges tend to keep the blade better aligned in the mortise hole leading to a cleaner cut with a little less effort, especially in contrary wood.

The following are some pictures of two of our Kakuuchi Oirenomi by Nagamitsu, hand-forged, of course, from Hitachi Yasuki Shirogami No.1 Steel (aka “White Steel).

36mm Kakuuchi Oiirenomi by Nagamitsu (Face)
36mm Kakuuchi Oiirenomi by Nagamitsu (Side)
12mm Kakuuchi Oiirenomi by Nagamitsu (Ura)
36mm Kakuuchi Oiirenomi by Nagamitsu (face)
36mm Kakuuchi Oiirenomi by Nagamitsu (Side)
36mm Kakuuchi Oiirenomi by Nagamitsu (ura)

Kakuuchi chisels take less time for a blacksmith to shape than the mentori oiirenomi we discussed in Part 2 of this series. The difference in shaping these two styles of chisels is the added step of grinding the extra bevels that make the mentori oiirenomi sleeker.

Indeed, most styles of Japanese chisels can be obtained with a kakuuchi cross section, including the oiirenomi version shown in my previous post, as well as atsunomi and usunomi, chisels we will examine in future posts.

Kakuuchi-style chisels take a little more effort to sharpen because the area of the bevel is larger, and more significantly, the area of the hard steel layer is greater, but on the other hand, they feel more stable on the stones.

More than a preference for greater weight, stiffness and stability, I suspect most individuals who prefer this old-fashioned chisel are making a fashion statement, something like “brogues not oxfords,” if I can adapt a movie quote.

In my opinion, they are not as elegant in appearance nor as handy as either the mentori oiirenomi or shinogi oiirenomi referenced in previous posts, but they do have undeniable dignity and presence.

What do you think?

YMHOS

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2 thoughts on “The Varieties of Japanese Chisels Part 4 – Kakuuchi Oiirenomi (角打追入鑿)

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