Takenaka Carpentry Tools Museum

The kanna is a tool used for shaving away surfaces of timber. The rectangular kanna that we see today was introduced in Japan around the mid-Muromachi era. Until then, a spear-shaped plane (yari-ganna) with a blade resembling a bamboo leaf is believed to have been the only plane employed to pare and finish timber. Japanese kannas are unique in that they function by being pulled, in contrast to the large majority of planes from around the world that function by being pushed.

The kanna is another tool that presents a wide variety of shapes and styles. In the case of the most widely used smoothing plane (hira-ganna), several different types of it such as the oni-arashiko-ganna, arashiko-ganna, muratori-ganna, chushiko-ganna, jyoshiko-ganna and the shiage-ganna are employed according to the different stages in finishing a surface. The choice of kanna also depends on the part of the timber that needs to be worked on, and here too the choice abounds: the most representative kanna types with different functionalities are the hira-ganna, shakuri-ganna, kiwa-ganna and the mentori-ganna, respectively used for smoothing, carving grooves, carving internal angles, and carving curved surfaces (all of these will be described in subsequent pages).

The kanna primarily consists of a metal blade (kanna-ba) and a wooden base or plane stock (kanna-dai). The base is sometimes produced by the carpenters¡Ç own hands but this is becoming increasingly rare and most are now produced by specialized carpenters. Oak (kashi) is the preferred material for making the base due to its hardness but this is subject to the personal preference of the user.

In general the blade that is used is an awase-kanna: a blade that is laminated with a second blade that suppresses surface irregularities created by shaving against the wood grain (osae-ba). The wide adoption of this kind of laminated blade is due to the difficulty at correctly using, cleaning and adjusting a kanna: highly skilled carpenters can create a smooth finishing without the aid of such a blade, but those who are less skilled are prone to producing irregular surfaces even using the awase-kanna blade.

Carpenters are highly sensitive about the sharpness of the kanna blade, as it directly influences operational efficiency. This perhaps accounts for the fact that many of the highly regarded blacksmiths are kanna producers. The tension between the performance of the blacksmith and the expectation of the carpenter may have helped to constantly improve the quality of kanna blades.