Servo motor following error video?

To anyone interested in making machines with servos:
This fellow I know does ornamental wood turning. One way of milling
helical grooves on a wooden cylinder works like this:
A lathe has a sprocket attached to the back end of the spindle. A
chain is draped over this sproket. One end of the chain is weighted,
the other end is attached to a cable. Said cable is run over various
pulleys and is attached to the lathe carriage. A spinning cutter is
mounted to the carriage. As the carriage moves back and forth the
spindle turns and the cutter, engaging the cylinder, milling a helical
groove. The pitch of the helix is changed by changing the sproket. So
this fellow was explaining this to me and mentioned that he wanted to
do this electronically. Use an encoder on the carriage to send pulses
to a servo or stepper driver which then controls the motor that spins
the spindle. He spoke with an engineer who told him that following
error would be so great that he couldn't move back and forth like he
could with the sproket arrangement. I didn't believe it so I built a
demo model with the signal generating encoder connected through a
precision differential to the motor shaft. Spinning the encoder one
direction causes the motor to spin in the opposite direction. If there
is no following error the the center section of the differential would
remain stationary. Any movement left or right would show following
error. Well, the center section does swing left or right. About two or
three encoder counts. At high count settings the amount of following
error, in degrees of rotation, is so small that it doesn't matter, and
is probably less than the windup in the mechanical version.  Using
encoders with switchable counts shows more movement of the diff with
the lower count settings. So, after that long explanation, would
anybody like me to try to post a video online demonstrating this?
Eric