鉋 Kanna
The Japanese Plane
At first glance the Kanna resembles the western plane, the earlier version with a body made of wood. The most obvious difference however is that the Japanese carpenter is pulling the plane towards him, rather than pushing it away, and is often working sitting down.
How did these differences arise? Try pulling a western jack plane towards you and it will soon dig itself into the wood. The Kanna will cut through the wood because its blade is much sharper.
The blade is made using similar techniques to the manufacture of the Japanese sword, combining a blade of hard steel, which is brittle and would easily shatter in use, with a softer steel that absorbs impacts on the sharp blade. The steel is heated and hammered, split and folded, and re-welded many times, resulting in more even distribution of carbon and less risk of failure due to voids or impurities.
The timber used in Japanese construction is often huge compared to western buildings, so the carpenter often has to sit astride it to work on it, and uses his body weight to pull the plane towards him.
The contemporary western plane uses three steel parts, blade, chip-breaker and lever cap, which allow the blade to be adjusted for depth and angle by a rotary control and a lever, and a cast-iron body for greater durability. The Kanna blade consists of two steel parts, the blade and a curved chip-breaker, which also functions as a wedge, so its adjustment is done by striking the wooden body with a small hammer. The body is made of harder wood and while the western plane has a flat base the Kanna is often shaped with subtle curvatures, to improve sharpness and control.
The result is that the Japanese carpenter can achieve greater accuracy in woodwork with the Kanna, the wood surface becomes smoother and is more impervious to water, and he can work while sitting on the tatami, or astride a giant beam.