Looking at a link provided here about steel belts for driving the
encoder shaft eventually led me to look a several web sites of
companies that produce stainless steel belts, or drive bands. It seems
that all the applications where a timing element, such as a toothed
pulley, are not used, belt creep occurs. This happens because the belt
is only moving at the same speed as the pulley for a small part of
rotation. On one side of the pulley the belt is stretched. On the
other it's compressed. A miniscule amount. But .0001" is also
miniscule. This is probably where the "backlash" comes from that I'm
seeing. Or, maybe belt creep and belt stretch. If I can get a little
free time I can find out what is really going on. I'll keep the group
posted.
Eric