I'm exploring the possibility of using a dc servo motor for my lathe spindle, I have the dc servo drive and the dc servo motor, as far as i know the motor does not have an encoder although i have the option of adding one to it from the manufacturer.

My question is, if my spindle allready has a 200 hole index pulse plate on the spindle plate currently used for the rpm / speed readout in mach3, why would I need an encoder on the dc servo motor?.

and i'm a little confused as to how mach3 connects and picks up information from the encoder as i thought the dc servo drive and motor was a standalone cell and all mach does is put signals 'out' to the servo drive.... wether they are step & direction or PWM.

The servo drive can also use tachy feedback from the motor, what is this?