Interessante kost en het artikel uit FWW maakt het wel duidelijker voor mij. Je zou dit bij een stalen schaaf net zo goed kunnen doen lijkt me. Al lezende kwam ik vanmorgen meubelmaker John Reed Fox tegen, hij staat in een lijstje op de FWW site. En van hem ook een verhelderend artikel over de Japanse schaaf. Hier de
link naar het artikel en hieronder de hele tekst. Ik was inderdaad zoals David ergens zegt, "wat kort door de bocht" maar zie in deze configuratie eigenlijk alleen maar een manier om de wrijving van de schaaf te verminderen. Het is geen gemakkelijke schaaf om over je werkstuk te trekken, de chinese variant met een stok er door is wat beter vast te pakken.
jaap
Japanese jointer plane sole configuration
I’ve had the great good fortune to be co-author with Bob Rozaieski on an article for the Arts and Mysteries column in the April 2011 issue of Popular Woodworking Magazine about Japanese and western planes, and the differences and surprising similarities between the two. I’ve received some questions about the setup of a long Japanese plane tuned for jointing a board (naga-dai kanna), as there are some sources that state that there are at least three touch points on the sole of the naga-dai kanna: the front, the front of the mouth, and the rear. For this sole setup, the two most important points are at the very front and rear of the body, and in the article I only reference those two points. Because of the main thrust of the article, and due to space issues, I didn’t elaborate on the touch point at the front of the mouth.
Here’s the setup for a smoothing plane, that we all know and love. Touch points at the front and in front of the mouth, with the blade sticking down a bit below the touch points. Keep in mind that for this and all of the other figures, the gaps are exaggerated for clarity, and all of the hollows are on the order of less than 0.01”, and that what looks like a rectangular hollow is really a very shallow curve.
Here’s the setup for a naga-dai kanna, as described by Toshio Odate in his book and many other places. Touch points at the front, in front of the mouth, and the rear all in a line, with the blade sticking down a bit just like in a smoothing plane.
Now, if there is a rear touch point that is in line with the front two touch points, and the blade sticks down a bit below the line, there’s really no way for the plane to cut and to have all three touch points hitting the wood at the same time, especially considering the mechanics of pulling a Japanese plane. The rear touch point wouldn’t touch because the shaving would have been cut away from the surface of the wood, and would hover above the board by the thickness of the shaving.
In fact, this would be the same situation as a plane with a perfectly flat sole at the level of the touch points, which would be the situation in a western plane. And with the mechanics of pulling a Japanese plane, since downward hand pressure is applied at the front of the plane throughout the stroke, the most important touch points would be the front and front-of-the-mouth touch points, making the rear touch point unimportant, and arguably unnecessary, except for maybe the last few inches of the end of the board, when the front end of the plane comes off.
The thing is, I don’t think Japanese woodworkers would have gone to the trouble of making the third, rear touch point if it didn’t have something to contribute. Otherwise, they would have just used the topography of a smoothing plane for truing up a board.
So I asked Odate about this at Woodworking in America in 2009, and showed him his book where he describes this. This is when he told me that for a naga-dai kanna, the blade is set so that the edge is in line with the front and rear touch points, and the front of the mouth touch point has a very slight relief about the thickness of a shaving, which is not in his book. I’ve tried to show this in this picture, but if it isn’t clear, the tip of the blade is in line with the front and rear touch points, and the touch point in front of the mouth is very slightly relieved.
This makes sense to me. For truing up a board, more length is better, whether you use a Japanese or western plane. By relieving the touch point in front of the mouth, you allow the rear touch point to do its job, and you’ve increased the reference surface of a Japanese plane to the entire length of the plane, instead of just relying on the length of the plane from the front to the front of the mouth. And I’m sure that Japanese woodworkers would not engage in activities that wouldn’t help their plane perform better (read: make a touch point at the rear of the plane) if adding this touch point didn’t help with truing a board. And physics dictates that extra length helps.
Again, the fact that the front of the mouth of the plane does not touch the wood to the same degree as the front and rear touch points might compromise the surface, but that is why you’ll follow this up with a smoothing plane. Likewise, a western try plane is not expected to leave a finish ready surface — that’s what a coffin smoother/infill/#4 is for.
Finally, I’ve tried this setup with an old standard length kanna. The rear touch point does seem to help with truing, and the plane takes slightly thicker shavings than a smoother, about 0.003-0.005”, just like I would expect a western jointer plane to do. It won’t take gossamer thin smoothing plane shavings, but that’s not its job. So there is some empirical evidence to support what Odate told me.
Still, technique is important, just like with western planes, and all the setup won’t help with bad technique. I approach truing the edge of a board with Japanese planes like Bob Rozaieski does with western planes: start taking shavings from the middle, working outwards, and then take full length passes until you get a continuous shaving. If you kept going at this point, you could get a convex surface, but this is true for western and Japanese planes alike.
Now, this is really not the main thrust of Bob’s and my article in Popular Woodworking, other than that for truing boards, Japanese woodworkers were trying to take full advantage of the length of their planes, and that for this purpose, longer is better, and that Japanese and western woodworkers both knew this, despite there being almost no overlap between those two woodworking worlds in the 18th century.
Update: Frank Vucolo pointed me to this article by Toshio Odate in American Woodworker from 1993, where he explains this in more detail.
