The Japanese plane / Kanna, a rudimentary yet subtle tool.

The Japanese plane / Kanna must be properly adjusted.

Japanese planes, called kanna, are rudimentary tools, yet subtle in their adjustments. They consist of a wooden block—most commonly Japanese white oak or, more rarely, red oak—a laminated high-carbon steel blade, and sometimes a chip breaker. Since the chip breaker is a more recent addition in Japan, there are many kannas that function without one.

A new Japanese plane requires a short series of adjustments before being put into service. First, the block (dai) must acclimate to the humidity of your workshop. Therefore, it can be left for a few weeks in a cardboard box (for premium kanna).

One must take the time to observe the geometry of the blade. It is much more complex than it first appears. Note its thickness, which tapers toward the bevel; its sides, which narrow; and its hollows, both front and back.

The different points for adjusting your Japanese plane / Kanna.

You can start by preparing what I will call the blade bed. This is the area where the back of the blade is in contact with the dai. It is essential to adjust this area to your blade, as the geometry of kanna blades is very sophisticated. Indeed, the back of the blade is concave, and its sides are not parallel but slightly beveled. This allows for more stability and enables the blade to be inserted with force for fine adjustments. To adapt the block to the blade, there is a simple technique consisting of applying a drop of oil and some graphite (using a pencil) to the back and sides of the blade. You then insert the blade with a mallet, and the graphite will deposit itself at the points of strong contact, including within the grooves. You will need to lightly scrape these areas using a file or a chisel with a burr.

The idea is to leave enough room for the blade to descend to within 10mm of the mouth. These last few millimeters are essential for finely adjusting the blade protrusion; if the blade is loose in its housing, this will be much more complicated. So, tight but not too tight—that is the balance to find.

The Japanese plane's chip breaker, a small part with a big result.

You must, of course, sharpen the blade and the chip breaker; I will come back to this in another blog post. However, you should know that the cutting edge of the blade must match the width of the mouth. Not the entire width precisely, but the width that allows the shaving to be ejected and which corresponds to the width of the chip breaker.

The sole of the Japanese plane and its adjustments.

There is one last point essential to the proper functioning of hira kanna: the adjustment of the sole. There are different types of adjustments for the sole, but two are primarily worth noting. One for rough jointing or making rather coarse shavings, and one for finishing pieces and making extra-fine shavings.

For the first, two contact points are needed. These both correspond to a 10mm strip at the front of the dai and in front of the mouth. The rest of the sole behind the mouth will remain out of contact, no more than 0.4mm from the plane of the sole. Between the two contact strips, you must create a recessed half-moon of approximately -0.3mm. This hollow can be shaped with a dai naoshi-kanna (a Japanese scraper also called tachi kanna), using the Tsunesaburo scraper available in our online shop, or with a stiff (thick) European scraper.

For the second type of adjustment for wood finishing, three contact points are required: the first two as mentioned above, and the last one aligned with the rear of the dai. In this case, you will create an oblique recession of -0.3mm leading up to the back of the mouth.

These hollows help to absorb imperfections in the wood and prevent excessive friction, while ensuring minimal contact surface when the sole is re-flattened. Yes, it is necessary to check the flatness of these contact points, as wood will always move over time.

Advantages of the Japanese plane / Kanna over the European plane.

So, what is the advantage of using a kanna instead of a European plane? There are many differences between these two planes, but hira kanna offer many benefits. We use them by pulling, which allows for greater control of the trajectory. The quality of the blades is undeniably better; the ura—the hollow at the back—allows for more efficient and faster sharpening. The high-carbon steel, or hagane, allows for such hardness that it is much easier to sharpen on water stones. All these characteristics make these Japanese planes an extremely effective and pleasant tool to use when one knows how to use them correctly.