Understanding Japanese Planes

Monday 9 July 2018

The Japanese love timber surfaces and the preparation of them is an important part of their woodworking culture. Finished objects often have exposed surfaces straight from the tool, similar to our Arts and Crafts aesthetic. The plane kanna that produces such surfaces is obviously key. In case you are confused between kanna and ganna, the letter k mutates to a letter g when a prefix is added as will be seen below.

Historians believe that the first planes were introduced to Japan from China and Korea and that these planes had no chipbreakers. These would have been harder to use than those with chipbreakers but some single-iron planes still exist and are used. All these planes have wooden bodies, known as dai, made of hard, carefully selected stable oak and morticed with a mouth across which a bar is fitted to retain the blade and chipbreaker.

One other vital point to mention at this stage is that Japanese planes are pulled towards you. This may sound cumbersome but I can assure you that it works.

Preparing planes for use

When a kanna arrives from the supplier it needs conditioning. Being a timber dai it may have shrunk and the sole might not be flat.

Setting blade

The first thing to do is to make the blade fit. The bed on which the blade sits is the omote-najimi, to either side of which is a groove to take the blade. This is the osaemizo. This groove determines the blade angle.

Setting the blade requires the osaemizo to be eased to give a hairs breadth clearance either side of the blade. Check that the blade sits snugly on the omote-najimi over its entire surface. Rubbing the back of the blade with a lead pencil before inserting the blade will leave pencil marks where the blade is tight. Ease these spots gently with a chisel. Do not force the blade into the body. It may take an hour or so to set the blade.

Once the blade and chipbreaker can be fitted against the metal bar known as the chipbreaker-holding pin or uraganedome, the sole can be checked. Turn the plane upside down and ensure that the irons are secure and also do not project above the sole. This test is done with the irons in place rather than with them removed because when fitted they will exert pressure on the sole and change its profile.

When you want to remove the irons tap on alternate sides of the front end at the same angle as the blade, with your index finger exerting a little pressure on the chipbreaker to stop it popping out.

Checking sole

The sole is then checked with a straightedge, longwise, across and diagonally, much as one would do to a western plane.

I have seen in a book that the sole can be rubbed over a sheet of abrasive mounted onto plate glass. The resulting scratches will show the high spots. I am sure this technique would work as well. The high spots are then scraped until the sole is flat.

I think the wooden-bodied plane allows you to use a handmade thick laminated blade which comes from a world-class tradition of blade makers and the wooden body polishes the surface being planed.

For those who value traditional blacksmithing as I do, there are blades available from famous blacksmiths on specialist websites. For details of the smith's spiritual approach see www.japantool-iida.com

Blade preparation

Start by lapping the back. On a good blade hardly any lapping should be necessary.

Then touch up the front on a fine stone. Again only a few strokes should be necessary, perhaps 30 strokes but each blade will vary.

Lap again to remove the wire edge. Learn not to keep transferring a wire edge from the back to the front and vice-versa. Stop as soon as the polish is balanced on the front and the back.

Chipbreaker adjustment

Now check that the chipbreaker lies flat. The soft corners of the chipbreaker are turned down when forged and can be adjusted to make the chipbreaker sit flat on the main blade so that no shavings ride up between the chipbreaker and the iron.

The kanna is now reassembled. To advance the blade tap it gently. To move it laterally tap it at the side. To reduce the projection, tap the dai once as if you were removing the blade, but this time tap the dai centrally. Each single tap will draw the blade back a fraction. After adjusting the blade push the chipbreaker down with your finger to make it wedge tightly.

Using the plane

As I have said above Japanese planes are pulled not pushed. Given that a western plane can be used in the pull fashion on a western bench, it is possible to use a Japanese plane in the same fashion.

You do not have to use a planing beam as Japanese carpenters do, but you could use one if you wanted to. For reasons of space, I use my normal bench. See pictures of various Japanese-style working positions adopted by American woodworkers in The Workbench Book by Scott Landis.

The grip is a little unusual so I show it in detail. This also shows some of the preparation of the timbers needed to make the small table, see right.