How to sharpen Japanese Chisels
What's special about Japanese Chisels?
The Japanese make their chisels with two layers of steel - one hard layer, to provide the blade, and a second, softer, springier one to carry it. The face of the chisel is hollow-ground, to make it easier to hone. The blade is angled slightly, so that it is possible to take out deeper holes than would appear from the short length of the blade. The steel being so much harder than we are used to in Europe, the blades are also more fragile than ours. Take care not to use them roughly or as levers.
A Japanese chisel (OIRE NOMI) is traditionally supplied ex-works neither sharpened nor fixed tight in its ferrule. It has always fallen to the user to convert it into a usable tool and thus make it his or her own. Nowadays the manufacturers have come round to supplying the chisels ready sharpened to a fine keenness with a resulting gain in time for the purchaser eager to use them.
How to fix the steel ferrule
Note: today most makers supply their chisels with this work already done!
The steel ring or ferrule which holds the wooden handle together under the blows of the hammer or mallet, has only been loosely attached. You should push it in far enough for it to allow about 1 - 2 mm of the tip of the handle to appear at the other end. It will usually have been supplied too tight and you will have to file or plane the wooden helve a little, to be able to push it on. If it is only a tiny bit too tight, you can also use a hammer to pound the wood on an anvil.
When it is over the end of the handle you can move it back down again a little by hammering. Then work on the edges of the protruding wood with a hammer so that they wrap around the ferrule like the cap of a mushroom and thus fix it permanently. The task will be make easier for you if you plunge the tip of the handle into water for several minutes once the ferrule is on, before you start hammering it.
Do not worry about using a metal hammer on the OIRE NOMI - that's what they do in Japan! What is important is that there is enough wood protruding above to prevent the clash of steel on steel. Some manufacturers supply now Japanese chisels who have the steel ring of these chisels already fixed. In this case you can skip this job.
To sharpen the blade
On no account use a dry-running grinding machine. Even wet-running grinders are little suited to this tool, as the bevel they make is hollow and will weaken the cutting edge. The best thing to use is a Japanese waterstone.
Flatten the face of the chisel first - always an absolute necessity for new chisels. Rest the blade with the face of the chisel flat on the grinding surface (either an absolutely flat stone or a steel plate with silicon carbon powder scattered on it), and move the blade over this surface until you can be sure you have taken a little off the entire cutting area. Do not grind to much of the face of the chisel away, or the hollow will be too much reduced and later honing made more difficult.
The next thing is to grind the bevel on a waterstone (grain size 800 to 1200). For Japanese blades, the correct angle is lightly less acute than for European ones. Take about 30° for soft woods and even up to 35° for hard woods.
Hold the chisel in your right hand. Push several fingers of your left hand (depending on the breadth of the tool) onto its face, right down by the bevel, so that its surface is pressed close and firm against the grinding stone. It is then possible to use your thumb to give the tool support from underneath. The best cutting edge is obtained by running the blade along the stone at either 90° or 30° to the direction of grinding. However, very narrow chisels (with cutting edge shorter than the length of the bevel) are an exception to this rule. Hold such tools in your right hand, as far back as possible on the handle, and while sharpening push them with the blade backwards and forwards. Using a grinding feed is perfectly legitimate - and is strongly recommended for beginners. Continue the sharpening process until a fine burr is produced on the edge.
Now - but not before - you can start actually to hone the blade. Take a stone with a grain size between 3000 and 8000, and grind the bevel and the flat face of the chisel alternately, several times, exactly as described above. The burr will fall away; the bevel and the face of the chisel will shine ever brighter as they become sharper and sharper.
Take care to dry the tool thoroughly after sharpening and, if then storing it, to oil it lightly so that corrosion does not set inch You will long have pleasure in your valuable tool.