Over in the RCM group I asked about the feasbility of using a master
slave relationship in a CNC lathe so a part could be machined on one
end and then switched from one chuck to another while spinning so the
back half of the part could be machined. Below is the post I made to
RCM with the first test results.

After the long discussion about one spindle following another and
using a Gecko 320 servo drive I have the first test results. The servo
motor has a 500 line encoder mounted on it and the Gecko Drive reads
it in quadrature for a resolution of 2000 counts per revolution. I'm
using another of the same model encoder mounted to another motor
powered by a PWM power supply. This motor is the master and the motor
controlled by the Gecko is the slave. The master encoder is connected
to an LS7184 quadrature clock converter. The LS7184 accepts the
encoder signals and outputs step and direction signals which are fed
to the Gecko 320. As the speed of the master motor is varied the slave
follows PERFECTLY! There is no perceptible (to me) lag or overshoot.
And when spinning the master encoder at approximately 1 rpm the slave
follows perfectly with NO cogging. When the slave is commanded to move
only one step it does so without jumping as would a stepper when
operated with just switches or by just touching the wires to a power
source. Obviously the Gecko ramps up to speed to make movement as
smooth as possible. In fact, even though the Gecko is fed only
discreet step by step motion signals and position feedback is only in
steps it acts like the whole system is analog, when the motor is the
only analog device in the system. It looks like I can now grab a
spinning part with two chucks at the same time without the worry of
scuffing the part.
Eric