Saturday, July 13, 2013

Sundials, and milling wood on a lathe

About a year ago I was into (as current argot has it) sundials. I made quite a few. Alas, one of them broke. It dropped on the floor, and the bottom portion of the dial itself broke. Sigh. Although the material cost on these things is zero, I have usually put in quite a bit of time carving the numerals and marking out the dials. The one that broke was an equatorial, too. Easiest to mark out,  hardest to get the inclination just right. The stylus (the pointy thing that casts the shadow) must be exactly parallel to the polar axis of the earth. That is, it must tilt at an angle equal to your latitude (62 deg in my case). Well, I decided to repair it. So the bottom part of the semicircle that forms the dial had broken off. I built a replacement piece out of scrap wood, and then I cut a groove in it with my tiny Lee Valley rabbet plane. Now I had to make the dial fit into the groove. So I set it up on the Taig lathe with a milling attachment.

The real problem with machine tools is not the machining itself. It is holding the blasted piece down while you machine it. The forces exerted by the machine are enormous, and will slew, jiggle, or skew your workpiece out from under you. As you see, I have an end mill held in the chuck of the lathe. Poor practice, by the way, but I have no collet big enough to hold the end mill. Bolted to the milling attachment on the lathe is the invaluable milling vise I got for Christmas. Thank you, my children. But to hold the dial still, I clamped a scrap board in the vise. This gives support to the dial. It is also clamped by the vise. There is a piece of paper under the vise. It miraculously keeps things from slipping, don't ask me why. Thanks a million to myfordboy for the tip. In the foreground, the slottted piece I must fit. Later I will cut it to shape. And to the scrap board I have attached a pair of very small C-clamps which (by serendipity) I found at a flea market a couple weeks ago. Very small clamps are hard to find. Now the dial is stable and I can mill it down to fit the groove in the slotted piece. I am actually routing on the lathe. Only we call it milling!

In the end it does not look so bad.

The stlylus now needs to be lengthened, or a new stylus made, because the shadow it casts is too short. Haven't decided yet what to do. But it was interesting, if not high-tech. And I didn't have to carve a new dial, which takes forever (art, not science).

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