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Japanese oire nomi: a simple modification

I posted this photo 11 years ago of six Koyamaichi "dovetail" chisels.

The three on the left were vintage Koyamaichi (circa early 1980), I picked up about 10 years earlier. The three on the right had been custom ground for me by Koyamaichi (via Stu Tierney, who ran Tools from Japan). Apparently this was treated with raised eyebrows at the time since Japanese "dovetail chisels" do not have fine lands. This is simply a name given to one type of bench chisel (oire nomi).

The new chisels had the special minimal lands …

... while the older ones retained their thick lands …

They are not much different from many Western bevel edged chisels: the lands are generally quite significant, and one would not wish to use them to make dovetails with tight angles as they would almost certainly bruise the edges.

I've been thinking about the lands on chisels of late as I design a drawer to house the sets of Kiyohisa slicks and oire nomi. The one area that I feel lets these chisels down is the thick lands, since they are less suited than some for working into angled walls or sockets, which forms a relevant part of the work I use them for This does not prevent them being used for many other tasks) …

Anyway, it got me thinking about a really simple modification that could be made to chisels with thick lands. I have not seen this done elsewhere, but then what do I know? I would be surprised if others have not thought of this ... just that I have not seen it.

I decided to modify the Koyamaichi chisels .... and planning on modifying the Kiyohisa chisels.

No doubt the thick lands are believed to increase strength and rigidity in a chisel blade. All of the chisels have sides which are 90 degrees …

What if we re-ground tham to .. say .. 6:1 (9.5 degrees)? This would retain the strength of a high side wall, but create a chisel that could slip into a a wide range of dovetails. The entire side of a chisel does not have to be ground, just small section.

To do this, I made a simple fixture for my belt sander …

Grinding like this is quite safe. Heat is kept down, and the grinding begins above the land. It is straightforward (with care!) to remove steel along the edge down to the edge of the back.

Here is a Koyamaichi with the sides ground to create a narrow land. It lost 0.1mm, or less, from each side.

The bright steel was returned to black with this converter …

One would not know that the blades have been modified 

Part 2: Proof of concept

As much as I respect and revere Kiyohisa as a maker, and as much as I recognise that I could be destroying the value of this chisels for a collector (if new, these chisels are around $250 - $500 each!), I am a user and believe that the chisels could be better for the lands being relieved. I do not do this lightly or impulsively. It has been on my mind for a long time. Finally, I decided to take the step.

I chose to test my skills on a 30mm Kiyohisa oire nomi which I recently restored. The blade is shortish, and ground at 25 degrees - all-in-all, not ideal. I have since obtained a new one with a full length blade and 30 degree bevel.

Here is the original, square side …

Here it has been ground at 9.5 degrees (6:1 ratio) …

From the front, can you see a difference between the ground side (right) and the unground side (left)?

Here is the left side, ground and steel blackened. I dare anyone to say it was breathed on.

But now it can work on dovetails as well. 

Regards from Perth


April 2021