Wednesday, September 5, 2012

Shaped planes, part VI, and ulus

The time rapidly approaches -- indeed, it is already here -- when I start making gifts for the people in my life. So there will be some stuff here that is intended as a Christmas gift. Ah, but for whom? You don't know, do you? My two previous ulu recipients know they are not included. Or are they? You are not to know. So, cloaked in anonymity we proceed.

First of all we are making a shaped plane. In fact, we are rebuilding a hollower. The old hollower worked. It was my first shaped plane and I am fond of it. But we learn. The blade was not sufficiently rigid. So I made a new blade. I deconstructed a circular saw. I will have some more to say about this. You have met this blade in Part V. You have also met the body. Now the task is to grind the blade to some sort of edge.

You might be able to see that if you just held the edge to a grinder (of any kind) the grinder would eventually grind your edge flat, like a chisel. Not good for something like a hollower. It has to be ground on a radius. Now Superman (tm) can do this in his sleep. Me, I need a jig. So I devised one. It is a piece of aluminum bar.
The aluminum bar is bolted to one of the fixtures that came with my TSO (Tormek-Shaped Object). For those of you that don't know, Tormek is a Swedish firm that resurrected the old-fashioned wet grinder. And patented everything. But their patents are expiring rapidly, and the asiatic manufacturers are into the game. Better for me! My TSO cost about a quarter of the original article.

Affixed to the aluminum bar, about a buck at any hardware store for far more bar that what you need for this jig, , is a common brad. For the record it is 1.7mm in diameter. So I had to drill a corresponding hole for a tight fit, and super-glue the brad in place. Then I use my faithful angulometer to set the proper grind angle. For a plane, 25 deg. I am entirely sure that Tormek makes a precision jig for just this purpose. I am equally convinced that I do not have to spend $100 or so for it!

Next shot may be superflous. It shows the jig, the grinder, and the blader. It does help if you file a little cutout right at the center of the radius of curvature.
Now you turn the grinder on. Do not forget to put the water tank in place. Do not forget to take the water tank off when you are finished, else you will distort your wheel -- it will absorb water on the stationary part. As you grind, rotate the blade. You use your fingers for this. Be sure you keep the cutout in the blade (the center of curvature) pushed up against the pin. Since the pin is the center of curvature you will grind a very nice circle. I cannot call it perfect because if you use a micrometer you will see I am way out. But for practical purposes I am really, really good. At this point I go to hand sharpening.

This plane will be back in the next epoisode of the drama. But in the meantime it occured to me that I had also solved another problem, namely, how to grind an ulu. Now an ulu is an "eskimo" knife. We do not use that word in Alaska, preferring to call the natives by their tribe or group. I love ulus. They are marvellous cutting tools. See some previous posts.

What I did really was to cut up a circular saw blade for other purposes. But every time I do it i think, "hmm, an ulu!" So I reserved about half the blade for ulus. They are gifts. For whom,? I refuse to say. Eat your heart out. Anyway ulus must be ground. And so our grinding jig evolves.
There is really no difference between an ulu and a convex plane blade. Both circular contraptions. Set the grind angle with the angulometer, and rotate the things. This jig is a little different. I found it convenient to drill a hole in the blade. It will be covered anyway by the handle. It is not in the exact center of curvature. But the error is small. A toolmaker's clamp holds the pieces of the jig together; otherwise it is the same as the previous jig -- but this version clamps both top and bottom. You rotate the ulu. same as with the plane blade, by hand, and it does a really nice grind.

Well, it has been a long day. To quote Mr Boswell, "and so to bed."

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