All the analogue (±10vdc) drives I currently use recommend the torque (current) mode of operation for CNC application.
A few decades ago velocity drives were common, and required a tach back to the drive, the encoder went back to the controller.
With these drives the velocity or inner loop (drive) had to be tuned first and then the outer (PID) loop in the controller was tuned.
It is claimed the velocity drive has looser control around the zero speed point.
I believe the main reason for the switch to trans-conductance or torque amps was due partly to the higher encoder frequency possibility and the sophistication of current DSP's etc?
With these Drives, the motor current is proportional to the ±10vdc signal in.
The switch is reflected in the fact it is very hard to obtain a DC motor with a Tach now, unless ordered as an option.
Going this route has worked out very well for me so far.
If you have the option of both with tach's in place you could do a compare.
If eventually going the Torque mode route you would disconnect the tachs, I usually also remove the tach brushes to avoid possible mechanical complications later.
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.