Re spindle rpm

If that is all you want, mount and drive a change gear in your chuck
and strobe it with a flourescent light. Divide the number of gear
teeth into 7200 and you know the RPM of the spindle. (like we did it
on the old phonographs, remember?) Make sure the speed is adusted
from the 0 side and that the gear teeth observed at strobe are the
same size as the real gear teeth so as to avoid reading a harmonic.

Most lathes have a gear already mounted on the left end and can be
used without any fuss. My lathe has a 45 tooth gear attached to the
spindle and that works out to 160 RPM, a good number to use as a
standard.

You can then use the years old trick of driving a small dc PM
motor/generator with a potentiometer connected across the terminals.
Using the method in the example above and the spindle running at 160
RPM, adjust the pot to make a voltmeter connected between one pot end
and the center pot terminal read 160 on a suitable scale
and it will correctly read any spindle RPM you will encounter. (
unless you screw up the pot setting). A suitable motor is available
from Radioshack at a few bucks. Richard