KOMI — The connection between the blade and the wooden handle of the Japanese chisel

Since Japanese chisels are sold with wooden handles installed, in the first few years of using Japanese chisels, I largely ignored the importance of the invisible part of the Japanese chisel,  the connection(Komi) between the chisel body and the wooden handle.

The Komi part(The Miki area in Japan is called "Nagago") of a Japanese chisel. This part is not visible when the chisel is fitted with a wooden handle.

As far as I know, in East Asia, the chisel has developed into a composite tool with a metal part and a wooden handle in the Shang Dynasty in China. The connection structure used is similar to the mortise and tenon joint, with a mortise made on the chisel and a tenon made on the wooden handle for connection.

"Most of the chisels unearthed from the Shang Dynasty have trapezoidal straight mortise holes, which were used to attach the wooden handles. At that time, people had already realized the elastic adjustment function of the wooden handles." - Li Zhen, "Traditional Chinese Architectural Woodworking Tools", 2004, p177

When I was learning to make Ming-style furniture, I bought chisels made by rural blacksmiths in China, and these chisels were connected using the above method. As far as I know, handmade chisels in China are still connected in this way. In relevant Chinese literature, the mortise  on chisels have a special term "銎/qióng". In Japan, this type of chisel is called "袋鑿/fukuro nomi" by carpenters.

Nowadays, the cross-section of the chisel's mortise is almost circular. However, due to the limitations of processing technology in the Shang Dynasty, the cross-section of the chisel mortise was mostly trapezoidal or quadrilateral, and it was not until the Warring States Period that it developed into a circular or oval shape.

"The cross-sections of the mortise and the chisel are both trapezoidal, indicating that the manufacturing capacity of the mortise at that time was still somewhat limited. ... Trapezoidal mortise was not used until the Warring States Period, and was replaced by round or oval mortise. However, in some places such as Henan, it was still used until the Jin Dynasty, and the shape of the utensils showed a tenacious inheritance of characteristics." - Li Zhen, "Traditional Chinese Architectural Woodworking Tools", 2004, p177

A bronze chisel from the late Shang Dynasty unearthed in Dasikong Village, Anyang County, Henan Province. Image from: Institute of History and Philology, Academia Sinica, Open Museum - 「https://openmuseum.tw/muse/digi_object/3e172be9643a45dcfa2a35d5f12043cd#202131」

In the years I have used Chinese chisels with this traditional connection to make furniture, although they have performed quite well in most of the work processes, it is inevitable that the wooden handle will come off or loosen from the chisel's mortise, and this often happens on chisels that need to be hammered frequently. Similarly, the Japanese "fukuro nomi" with the same connection structure has the same disadvantages ー

"That is, the handle is easy to come off or loosen. The handle is struck with a hammer or wooden hammer, a mortise hole is dug, and the chisel is hammered into the wood, and then it is pried back and forth and rocked. Therefore, the wooden part of the cone that is inserted into the hollow part (mortise) of the chisel cone will become loose, no matter how tightly it is joined." -- Noboru Tsuchida, "The Shape of Carpentry Tools - About Chisels ①", Knife Magazine, 2008 No. 12, p47

A Japanese "fukuro nomi" from the Edo period by unknown smith, the round mortise are made very finely.

For this reason, Japan developed a chisel that also uses a mortise and tenon structure, but the connection structure between the chisel and the wooden handle is opposite to the previous "Fukuro nomi" -  a mortise hole is made on the wooden handle, and a tenon (komi) is made on the chisel body to connect. This structure greatly improved the shortcomings of the "Fukuro nomi".

After the Edo period, the "Fukuro nomi" became increasingly rare, and was replaced by a komi-style chisel with a wooden handle that is not easy to loosen or come off.

It is difficult to determine the time when the Japanese komi-style chisel appeared. However, from the surviving komi-style chisels made by skilled chisel blacksmiths at the end of the Edo period, which are both beautiful and functional, it can be seen that the chisel blacksmiths before the end of the Edo period had already had considerable production practice and technical accumulation for this type of komi chisel for a long time.

Komi can be roughly divided into three shapes as shown in the figure below: quadrangular pyramid(left), obelisk(center) and cannonball(right).

Among them, the quadrangular pyramid-shaped komi appeared the earliest and is the easiest to make. However, the quadrangular pyramid-shaped komi is still not ideal in terms of connection strength. In the late Edo period, skilled blacksmiths improved the quadrangular pyramid-shaped into an obelisk shape, which improved the connection strength. But the most ideal is the cannonball-shaped komi. This kind of komi with a curvature on the top fits more evenly with the mortise of the wooden handle, and the wooden handle has a higher bite force on the komi.

・Quadrangular pyramid shape komi. This chisel from the Edo period was made of Japanese iron and Tamahagene.

・Cannonball shape komi. This chisel from the Meiji period.

From my experience removing wooden handles from chisels, the quadrangular pyramid-shaped komi is easiest to remove, followed by the obelisk shape, and the most difficult to remove is the cannonball shape.

In addition, I will share two poorly made komi. The first komi was crooked, which caused the wooden handle of the chisel to be out of line with the chisel blade.

The second tenon was made too thin. Although this made it easier to attach the wooden handle, the connection was weak and more likely to break.