Projectus stallis

I’m working on another comparator, because I just love things that measure and this will help me learn how to make things that move precisely and repeatably. And it ain’t easy. I’ve got a head unit that works (ie the horizontal movement) but the I’m a bit stumped on the vertical component.

Here is where I’m at:

The interesting bits are: a 40tpi screw (same as on micrometers), an adjustable dovetail (with a piece of plastic for a gib as the steel/brass combo isn’t as smooth as I’d like), a sort of interesting way of attaching the sliding part (ie nut) to the screw (see if you can figure it out – the other end is the prototype) and an interesting and easy way to do simple engraving.


For the thimble, just to figure out how to do it, I wanted graduations.  I picked 2½ thousandths (of an inch) because that is an even divisor of a circle (one full turn is 0.025″, 0.005″ is 72°==360/5, 0.0025″ is 36°). I could then mount the thimble in the spindexer and engrave the lines. I don’t have a graver so I hit on the idea of using a center drill as a small endmill, worked fine, leaving a fat shallow groove).

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