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 sunlight in a day.

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 wooden 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.

In any case, hand-operated powertools tend to be less-precise than large CNC machines, leaving rougher surfaces and tolerances that often need fine adjustment without messing around. This is where the ootsukinomi excels because, with the combination of its sharp blade, long handle, and the power of the user’s back and legs, it can quickly gouge out large swaths of wood when cutting joints. But make no mistake, for it is not a brutish tool like an axe or adze, but can deftly pare fine shavings to achieve precise dimensions for tight fitting joints and smooth finished surfaces due to the angular control the longer blade, neck and handle afford the accomplished craftsman.

Sharp tools guided by human hands, controlled by human minds with years of experience are indispensable in the final analysis.

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 in shinogi profile for paring the housed dovetail joints to house beams and purlins commonly used in Japan, 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. 

As mentioned above, 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.

Mitsuura

When paring large surfaces with the wider ootuskinomi chisel the hollow ground ura may allow bumps in the wood to slide up into 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.

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. 

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.

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.

YMHOS

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Links to Previous Posts in this Series

• The Varieties of Japanese Chisels Part 1 – The Main Categories
• The Varieties of Japanese Chisels Part 2 – The Mentori Oiirenomi (面取追入鑿）
• The Varieties of Japanese Chisels Part 3 – The Shinogi Oiirenomi (鎬追入鑿）
• The Varieties of Japanese Chisels Part 4 – Kakuuchi Oiirenomi (角打追入鑿）
• The Varieties of Japanese Chisels Part 5 – High-Speed Steel Oiirenomi (HSS 追入鑿）
• The Varieties of Japanese Chisels Part 6 – The Mortise Chisel (Mukomachi Nomi 向待鑿)
• The Varieties of Japanese Chisels Part 7 – The Nihon Mukomachi Nomi (二本向待鑿)
• The Varieties of Japanese Chisels Part 8 – The Atsunomi （厚鑿）
• The Varieties of Japanese Chisels Part 9 – The Uchimaru Nomi Gouge （内丸鑿）
• The Varieties of Japanese Chisels Part 10 – The Sotomaru Nomi Incannel Gouge （外丸鑿)
• The Varieties of Japanese Chisels Part 11 – The Tsuba Nomi Guard Chisel (鍔鑿）
• The Varieties of Japanese Chisels Part 12 – The Usunomi Paring Chisel (薄鑿)
• The Varieties of Japanese Chisels Part 14 – Kote Nomi (鏝鑿Trowel Chisel)
• The Varieties of Japanese Chisels Part 15 – Ootsuki Nomi 大突き鑿
• The Varieties of Japanese Chisels Part 16 – High-speed Steel Atsunomi
• The Varieties of Japanese Chisels Part 17 – Sokozarai Chisel
• The Varieties of Japanese Chisels Part 18 – The Hantataki Chisel