"R. O'Brian" wrote in message
news:JBy0f.407$784.353@lakeread08...
next. However, I think the problem is hysteresis in the rubber belt
driving the encoder from the carriage. We'll see.
Eric

You probably need a metal belt, a thin flat endless ribbon of stainless
steel or some such alloy. Dimensional stability is excellent at constant
temp. See
http://www.machinedesign.com/BDE/mec...emech1_20.html

Or phosphor bronze... I can see that working for partial turns, but not
multiple turns as Eric is looking for. Two opposing straps wound not quite
the full circumference, fixed firmly at the ends, will track like a worm and
rack.

It would be instructive to disassemble a dial indicator and look inside.
Mebbe I would just find a way to mount the encoder to the de-faced
indicator, rather than mess with mirrors, lasers, belts, oscilloscopes,
quadrature waveforms, ... unless the idea is to mess, to reinvent, rather
than measure.