Part 4 of a British Introduction to Japanese Planes
Fitting the blade and back iron to the body is a fiddle, but not difficult. What you need is a good bench light and a graphite pencil or graphite stick. The essence is of this is DO NOT CHANGE THE GEOMETRY of the plane body. So as the blade fits into the two side channels, do not pare the upper surface; this is the surface that beds the blade at 41° effective pitch.
Remove the bar under which the back iron fits. You will find that this is just a round wire nail sharpened on one end. Fit the blade by rubbing graphite on the sides and on the back of the blade.
Tap the blade in using a small hammer, tap it out by hitting the top back corner of the wooden body with the hammer, there is a chamfer planed on that corner to allow you hit JUST THERE. Not on the end like European tap-and-try planes.
Pare away the area where the graphite has left an imprint on the plane body and repeat the process. You will find yourself fitting the width first, then paring to allow the back of the blade to sit further down in body of the plane. Allow a nice couple of hours to do this well. If you rush this, the blade will not sit tight and you will not get the polish you want.
Remember that plane bodies expand and contract in width and blades do not, so open the side channels enough to allow for this expansion and contraction. You see so many cracked Kanna where this has not been done correctly.
Getting a good fit for the back iron is difficult as it is hard to see right down by the cutting edge. You will need a narrow chisel to work the slots on either side and a broad chisel for the land between.
The mouth is pretty well determined by the Kanna’s maker; a good maker will set up the mouth so that the blade trims its own mouth and you can then open it a shaving or two. I have a Kanna that did not have such a good mouth so I have fitted a rosewood dovetailed key in front of the blade.
Next we will look at the sole of the plane and taking a shaving or two!
— David Savage, http://www.finefurnituremaker.com