Can you address whether shinogi oi ire nomi are "dovetail chisels" as they have been called in the West? My earlier teacher hated that name, and thought they were completely unsuitable for that task. Were dovetails for casework traditionally chopped and pared with these tools?
Excellent question. I would differ from your earlier teacher's assessment that the shinogi form chisels are "completely unsuitable" and prefer to say they are not perfectly suited for the task out of the box, so to speak.
Dovetails may be chopped and pared with either
shinogi-form or
umeki-form chisels. When you receive a
shinogi-form chisel from a blacksmith, the cross section looks like this:
- chisel cross section for dovetail.jpg (23.64 KiB) Viewed 6219 times
Note the part marked with the arrow, termed
koba '
小端'. You can see that the intersection between the side of the chisel and the
ura is not a crisp corner. A chisel side is made this way because (and just like the tip of the chisel), if the side arris were sharp after forming to shape, then the process of tempering would disproportionately affect the sharp arris, making it too hot. This would later result in a chisel which has a crumbly side edge. That arris needs to therefore be left blunt for the heat treatment phase. When chisels are formed, the tip is left blunt for the same reason, then shaped to a sharp point after the heat treatment process is complete.
After heat treatment, the smith does not similarly grind the side of the chisel to a sharp point for the reason that, in most usages, it makes for a tool which will readily slice the side of your finger open - the same side of your finger you may use to guide the tool when paring. For most usages, you wouldn't want the side arris to be razor sharp. However, if you want to cut dovetails or similarly acute inner corners, then grinding the edge of the tool into a sharp arris would be the thing to do:
- chisel cross-section change.jpg (38.37 KiB) Viewed 6219 times
(images from Mandara-ya's site).
Generally speaking, if you had a set of 10 chisels, you would only need to modify a couple of them with sharp arrises specifically for the task of cutting dovetails.
This is the thing with Japanese tools that makes them a harder sell in the west. The come a bit as a kit, and the user can modify them to suit requirements. It's normal for Japanese carpenters and woodworkers to make their own plane
dai and customize their tools in various ways, whereas in the west there is far more an expectation that the tool come out of the box ready to go. I think a large part of this seeming difference in expectation arises from the fact that the chisel buyer in Japan is generally a profession who works full time with the tool, while in the west the typical buyer is a hobby woodworker, new to things, and reading magazines which always tout some new and easier way to do stuff.
If you wanted to order chisels with the arris formed to a sharp corner, you could do so, however this option is generally only available by working with a retailer who is able to communicate your particular requirements to the smith.