The Varieties of Japanese Chisels Part 15 – Ootsuki Nomi 大突き鑿

All times are good for those who know how to work and have the tools to do so.

Carlos Slim

The Ootsuki nomi is the largest of the Japanese chisels. It is essentially a scaled-up tsukinomi paring chisel, equivalent to what is called a “slick” in the West.

Definitions

The name is written 大突鑿 using Chinese characters. The first character 大 means “large,” or “ big.” Besides “Oo “ this character can also be pronounced “dai.” You may notice it looks like a man with his legs spread and arms extended, as if he is describing to his buddies the size of the fish that got away. At least that’s how I remembered the meaning when I was a young man in Japan many moons ago.

The second character 突 means to “push against.” And the last character 鑿 , pronounced “nomi” means chisel. It is a very complicated character the origin of which is a mystery to me and everyone I have asked.

So the name translates directly to “large push chisel.”

Applications

If you have never done timber framing, a brief explanation may be helpful. 

When doing production work (versus hobby stuff) one cuts the pieces and parts of most open joints using electrical circular saws. Chainsaws kinda work too, but with much less precision.

Handsaws are also necessary for some cuts, but for most situations a circular saw is much quicker and less tiring. There’s a lot of wood that needs cutting after all and only so many hours of daylight.

Mortises are typically cut with portable electric hollow-chisel machines. There are other options such as portable chainsaw mortisers, stationary router machines, or the amazing German Hundegger machines. http://hundeggerusa.com

I once worked for a Japanese company that cut entire structural frames using CAD driven CNC machines in a factory. In that situation however, the CNC machinery, while very precise and very quick, was so expensive and so inflexible that the building had to be designed around the repertoire of joints and sizes the machinery could cut rather than the joints required to make the best building. And it could not handle significant dimensional irregularities in the timbers used, so only machined glulams were suitable. A very limiting endeavor indeed. I left that job after 2 years.

Sharp tools guided by human hands, controlled by human minds with years of experience are more flexible.

Paring a saddle
Paring a splice joint with a 48mm chisel
Paring a housed semi-half-lap notch where two beams will cross over and under each other

Indeed, handtools like axes, adzes, chisels and handsaws are necessary especially when doing “ round work” in logs or when the design calls for irregular-shaped timbers. Paring chisels are also needed to achieve the relatively precise tolerances and smooth surfaces such work demands.

Ootsuki nomi are relatively heavier than other Japanese paring chisel with larger diameter and longer handles. They are  built to resist the large bending moment forces created by a large man gripping the handle with both hands and pushing like a plow horse to pare wood. This is the task this chisel excels at.

Most Japanese carpenters that use this tool buy them in sets of two: a wide 48~54mm wide one for paring open joints and the sides of mortises, and a narrower 24mm chisel, although other sizes are available. I have owned a custom 2-pc set hand-forged for me by Mr. Shimamura (Kiyotada) many years ago, one with a 60mm blade and an extra-large handle intended for working especially large North American  timbers. 

The 24mm chisel is used for paring standard rectangular mortise, dovetail mortises and dovetail tenons, besides a hundred other tasks. In cross section, it is essentially a large shinogi usunomi chisel to help it get into tight places.

A carpenter paring the end walls of a mortise with a 24mm ootsukinomi chisel

Mitsuura

When paring large surfaces with the wider ootuskinomi chisel the hollow ground ura may allow bumps to slide in the hollow-ground ura unseen escaping paring requiring multiple passes to knock them down. This sneaky behavior is easy to overcome with practice, but some people prefer an ura with not a single, but multiple grinds with lands between each hollow-ground area to help index the blade and shave these bumps the first time.

I believe this is one of the few situations where these multiple ura, called mistuura or “triple-ura” are useful.

Kensaki (swordpoint) Ura by Sukemaru. A very unique style of mitsuura cut with EDM equipment. Pretty cool, huh. Sadly, Mr. Usui no longer does this detail no many how hard I beg him to.

Some people like the unusual appearance of mitsuura. I must admit they look sexy in wide blades, but they have some downsides. The first downside is that, because there is more hard steel in contact with the stone, mitsuura blades can take a little longer to sharpen.

Second, they can be a little harder to keep flat. Neither of these are difficult problems to overcome. But the third downside is more problematic. 

A worn-out mitsuura oiirenomi

Because the three hollow-ground areas are shallower and have less total volume than a single ura, they tend to wear out and disappear sooner. This is not a serious deficiency unless you use and sharpen a mitsuura chisel a lot, or have a heavy hand when sharpening the ura. The negative impacts are minor in most cases.

Beloved Customers need to be aware of these peculiarities and to be gentle when sharpening mitsuura blades.

C&S’s 24mm Ootsukinomi. Notice the shinogi shape

These are not chisels most people will ever have need of but as long as humans are doing timber framing, there will always be a demand for this unique tool.

C&S’s 24mm Ootsukinomi (face)
C&S’s 24mm Ootsukinomi (side)
C&S’s 24mm Ootsukinomi (Ura)
C&S’s 48mm Ootsukinomi (mitsuura)
C&S’s 48mm Ootsukinomi (side)

YMHOS

Links to Previous Posts in this Series

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2 thoughts on “The Varieties of Japanese Chisels Part 15 – Ootsuki Nomi 大突き鑿

  1. I like seeing the photos of the japanese carpenters using these style of chisels. Both hands on the handle or one on the handle and one around the ferrule. I feel a lot of people may be more likely to want to have a hand up near the shoulder or close to the blade. When I started using japanese chisels, especially for paring tasks I used to get slices on my index finger from where I was using my finger as a support for the chisel. I’ve changed my hand placement and no more cuts for my index fingers! 🙂

    Like

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