Japanese chisels — 鑿, nomi — occupy a special place in traditional Japanese toolmaking. At first glance, two chisels may appear almost identical: the same forged steel blade, the same wooden handle, the same bevel at the back… Yet, a few millimeters and a few metal facets can significantly alter their behavior in wood.

Among the terms most often encountered when looking into Japanese nomi are Kanto, Kansai, mentori (面取り), and kakuuchi (角打ち).

But what do these terms really mean? And above all, which shape should you choose for your woodworking?

The Japanese nomi: a tool with a unique construction

Before comparing the different shapes, let's quickly recap what makes a Japanese nomi unique.

The traditional Japanese chisel is generally composed of a thin layer of hard steel welded to a body of softer steel. This construction allows for a very hard and very fine cutting edge while maintaining a certain capacity for shock absorption.

This is one of the reasons why Japanese nomi can be used with a mallet for mortising and joinery work.

The term nomi (鑿) simply means "chisel." There are many, many families of nomi: oiirenomi, atsunomi, usunomi, tsukinomi, mukomachinomi, etc.

In this article, we are primarily interested in the exterior geometry of the blade, and in particular two shapes found on oirenomi (追入鑿): the mentori and the kakuuchi.

Mentori: the Japanese chisel with chamfered edges

面取り — mentori literally means something like "to create a chamfer" or "to break an edge."

On a mentori oiirenomi, the four longitudinal edges of the blade do not remain at perfect right angles. They are slightly chamfered.

Visually, this gives the chisel a more elegant and slender silhouette.

This geometry is extremely common on Japanese oire nomi today. In fact, the mentori oire nomi is the most popular form among modern oire nomi.

Why chamfer the sides?

The chamfer has several consequences.

First, it reduces the amount of metal present at the corners of the blade. The chisel appears lighter and more slender.

But above all, the side edges are less likely to rub against the walls of the wood when working in a mortise or a joint.

This can make the chisel particularly pleasant for finishing work and precise joinery.

The flip side is that manufacturing requires more work: after forging and shaping the blade, the blacksmith must also create these additional facets.

Kakuuchi: the square-section nomi

At the opposite end, we find the 角打ち — kakuuchi.

The term can be translated literally as something like "box shape," and describes the geometry of the blade here: the exterior edges remain much closer to a right angle.

The kakuuchi oire nomi is an older form. Its section is essentially rectangular, with four relatively square exterior angles. The difference becomes particularly obvious when placing a mentori and a kakuuchi side by side.

Mentori:

chamfered edges → more elegant and streamlined section.

Kakuuchi:

retained edges → more massive and square section.

Kakuuchi or mentori: which is more efficient?

There is no real "best" choice. Both geometries prioritize slightly different qualities.

The kakuuchi is more massive and rigid. Its relatively square edges can help keep the blade well-aligned in a mortise, especially when working in difficult wood or against the grain. Covington & Sons specifically highlights this advantage for mortising work.

The mentori, conversely, offers a more streamlined and refined feel. The chamfers reduce the surfaces susceptible to coming into contact with the walls of the mortise.

This is also one of the reasons why the mentori has become the most widespread form.

In summary

The kakuuchi is not just "a cheaper model"

It would be tempting to view the kakuuchi as a simplified or budget version of the mentori.

However, that would be reductive.

Manufacturing a kakuuchi does indeed require fewer finishing operations since the additional chamfers do not need to be made. But this geometry also has its own distinct qualities.

Its mass and its sharper edges give the chisel a sense of solidity and stability that some artisans specifically look for.

The kakuuchi can therefore be chosen for its own characteristics, not solely for its price.

A Japanese source dedicated to terms used by carpenters also describes the kakuuchi as simpler to produce and potentially interesting for rough work, while noting that the mentori offers a better feeling of penetration.

And what about Kanto and Kansai?

This is where things get more interesting — and a bit more complex.

The terms Kanto (関東) and Kansai (関西) refer, in their primary sense, to the Eastern and Western regions of Japan. These regional distinctions are found in many traditional Japanese tools and objects.

However, unlike mentori and kakuuchi, which quite directly describe a geometric characteristic of the tool, the terms Kanto and Kansai can be used less uniformly depending on the manufacturers, regions, and families of tools.

Therefore, one should avoid presenting "Kanto" and "Kansai" as two universal standards for the Japanese nomi.

In the Japanese tradition, regional differences can concern shape, proportions, manufacturing habits, or even the way the tool is used, rather than a single characteristic easily summarized in one definition.

This is an important point when choosing Japanese tools: the name of a shape does not always tell the whole story of the chisel.

A question of geometry… but also of feel

For a Western woodworker accustomed to European chisels, the difference between two Japanese nomi may seem minimal on paper.

But in the hand, it can become very perceptible.

The weight of the blade, its rigidity, the shape of the sides, the width of the neck, the thickness behind the cutting edge, and even the way the handle is fitted all contribute to the feel of the tool.

This is why two nomi of the same width can have very different behaviors. And this is also why Japanese artisans have developed such a large range of specialized shapes.

The principle is simple:

the right tool is not necessarily the one that does everything, but the one that is specifically adapted to the work one is currently performing.

Which nomi to choose?

For someone wishing to start with Japanese chisels, the mentori generally constitutes a very versatile choice.

It is particularly well-suited for:

• traditional joinery;
• mortising;
• hand work;
• finishing joints;
• general cabinetmaking and carpentry work.

The kakuuchi, on the other hand, will appeal more to those who appreciate:

• a more massive feel;
• a very rigid blade;
• stability in mortises;
• a traditional geometry;
• the historical character of old Japanese tools.

So it is not a question of choosing between a "good" and a "bad" shape.

It is rather a matter of choosing between two geometric philosophies.

Kakuuchi or mentori: two expressions of the same tradition

What makes Japanese nomi particularly fascinating is precisely this ability to evolve a tool without abandoning its fundamental principles.

The kakuuchi represents an older, robust, square form that is very present in the history of Japanese toolmaking.

The mentori represents an evolution toward a more worked, finer geometry that is now extremely widespread.

The kakuuchi was the standard shape for Japanese chisels until approximately the second half of the 20th century, before the mentori shape became much more popular.

And perhaps that is one of the best ways to understand the difference:

the kakuuchi and the mentori are not two competing tools. They are two different responses to the same question: how to build a Japanese chisel that is robust enough for striking, precise enough for joinery, and fine enough to cut wood cleanly?

Key takeaways

鑿 Nomi
The general term for a Japanese chisel.

追入鑿 Oiirenomi
The versatile joinery chisel, very common in Japanese workshops.

面取り Mentori
A geometry with chamfered longitudinal edges. Finer and very widespread today.

角打ち Kakuuchi
A more square, more massive, and historically older geometry, particularly appreciated for its rigidity and stability.

Kanto / Kansai
Regional appellations whose meaning should be interpreted with caution depending on the manufacturer and the type of tool.

To learn more

At Outinomi, we believe that understanding the geometry of a tool is just as important as knowing its steel or the name of its blacksmith. A good Japanese chisel is not just a piece of extremely hard steel: it is a coherent ensemble of geometry, forging, tempering, balance, and craftsmanship.

It is this understanding that allows one to choose the nomi adapted to their work — and above all, to understand why two chisels that seem almost identical can behave in very different ways in wood.