The completed cheap disk drive
Here's a photo of the disk drive. A six-inch ruler is in the bottom right corner to give an idea of the scale. The compass is held in place by two nylon screws (don't use any magnetic material near the compass; use brass, aluminum, or nylon or some other non-magnetic material). The diameter of the drive is dictated by the diameter of the Lazy Susan bearing, which you can see peeking out at the lower edge of the plywood circle. If you look carefully, you might be able to see the nylon screw at the top left corner of the compass (there is also one on the top right corner but it doesn't show up as well).
Nails don't have much magnetic retention. I usually stroke them right before giving the talk. The compass is only approximately pointing to the nail because I magnetized it two months ago, and I didn't notice the magnetism had worn off until I pasted this photo into the Web page.
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Copyright © 1999 The Joseph M. Newcomer Co.
Last modified: March 20, 2003