Beam Compass

I made the locking rings (part 3) and the adjusting ring (part 8) from 1 inch diameter aluminium turned down to 22mm diameter for a length of at least 40mm to make all four rings.

- Stewart Hart

These rings would normally be knurled but instead of knurling I decided to mill 12 finger grips along the length of the bar with a ¼ inch bull nosed slot drill using the spin indexer. The bar was then loaded back into the lathe, the smaller M3 hole for the adjusting ring drilled and tapped first, some neat chamfers added and then parted off to length. Then I drilled and tapped the locking rings ½ inch x 32ME, chamfered them and parted them off to length (photos 9 and 10).

Here’s another little trick for putting the chamfers on the rings. Make yourself a form tool, use it to chamfer the front then, before you part off, chamfer the back. At the same time, you will be chamfering the front of the next ring this way you won’t have the problem of trying to chuck the thin part for chamfering the back (photo 11).

You can make the beams (part 5) any length. I made mine 300mm and, when they are screwed together, I can draw 1m diameter circles, although I doubt very much I’ll ever need to draw a circle that size. All you have to do is turn and thread one end M5 and drill and tap the other M5. The second beam only needs the male thread (photo 12).