Hi Jim,

Yes, I know I shouldn't have done it, but the surface was very smooth...
(hangs head in shame).

I agree, it seems a bit strange to be able to measure (and visually
interpolate below) 1 micron with a workshop tool (after all, the
wavelength of light is abour 0.6 microns), but there you go. The body
divisions are 1 and 0.5 mm, the 50 thimble divisions are a decent size,
and the physical movement to get from one vernier division to the next
is enough that I can interpolate to 0.2/0.3 (under a mag-lamp). I don't
know what Mitutoyo claim for absolute accuracy, but it's very repeatable
and certainly makes for close comparisons.

No, I most certainly didn't even touch the chuck key.

Roger

jim rozen wrote:
In article , rlincolnh says...


a little I use my Mitutoyo 0.001mm vernier micrometer to measure the
work - ok, the absolute value is a little out, no surprise, but the
diameter is constant to within a small fraction of 1 micron i.e. approx
0.0002/0.0003mm along the length of the 50mm cut.


Not really what you were getting at, but I'm a bit suprised you can
read a vernier caliper to within one micron. Are you postive
you are interpreting the readings correctly?



Then, just for the hell of
it, I mounted a DTI (0.01mm per division) on the carriage and rotated
the chuck by hand. Shock and horror - I see just under 1 division (~
0.008/0.009mm) fluctuation per rev. It's totally consistent, and if I
move the carriage along the length of the 50mm the DTI behaviour remains
identical. I ran the lathe at the lowest speed (70rpm), and the DTI
response is exactly the same, right along the 50mm length.


Hmm. First off don't run the dial indicator on the workpiece
under power. That's bad for it.

Did you remove the workpiece from the chuck, and then replace it
there before performing this test?

Jim