This make a good case for dual independent encoders. motor
shaft/ballscrew, ballscrew/glass scale, steps/glass scale, etc.
Just for grins I tried the hand crank on my well used (Boeing then trade
school, the auction) defunct tracer mill converter by a Russian engineer
to cnc for the trade school. 1963 vntage cinci. Comparing the hand crank
on the X vs a accurite 5 um glass scale they were dead on (of course
only in one direction) ;-) The Y was a mess so I didn't try it.
It is relatively easy to clamp a glass scale to the bed, dial it in
parallel to the axis then tie it to the spindle with the spindle power
carefully disabled and proceed with measurements. Notice I did not say
much about a Chinese glass scale. Some are good some not so good. You
pays your money and takes your chances.
Dave
On 10/5/22 7:53 PM, Jon Elson wrote:
Wow, it gets deeper!
It is NOT the encoder, or anything in the encoder-reading process.
I marked the motor shaft, and the motor is returning to the exact same
position every cycle.
Well, I tried a different indicator and mount, and the problem was in
the indicator mount! I was using an old knock-off of an IndiCol that
clamps around the spindle nose or end mill holder and has several rods
with locking thumbnuts on them. These swivel joints were slipping
just a tiny bit each time the vise touched the indicator, even though
they were PRETTY tight! Ugh, 3 days of going around in circles trying
to tell where the issue was!
Jon
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