In article ,
Dave Martindale wrote:
I recently bought a used micrometer of a design I've never seen
before. The only manufacturer's identification on it is the Greek

[ ... ]

The micrometer has both the usual scales on the thimble and a
mechanical digital counter display. The thimble reads in mm, the
mechanical display is in inches. The mechanical display is driven by a
V-groove cut into the spindle, like the Mitutoyo mechanical digital
mikes. However, this V-groove is *not* a simple groove parallel to the
spindle axis; it is a slight helix! Does anyone have the comparable

[ ... ]

The V-groove is effectively a helical cam that provides a very small
rotational motion, just enough to compensate for the error in the gear
ratio chosen. It works, but it must be more complex to machine than a
straight groove parallel to the spindle axis. Does anyone else do this?
Why not use 63:32 ratio gears instead?

I don't know for micrometers, but I have seen a Gertner (sp?)
travelling microscope (a microscope mounted on a carriage for a
lathe-bed style optical bench) with a long horizontal travel with a
micrometer leadscrew. But the nut is captive end-to-end, but free to
rotate, except for a radial rod which engages a groove in a bronze bar.
That bar has fine setscrews to adjust the angle relative to the axis of
the leadscrew so it introduces very small corrections into the pitch of
the leadscrew. All in all, a very precise bit of metalworking -- and
*very* expensive. :-)

Enjoy,
DoN.
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