Hi I was wondering if MACh3 supports using a stepper or servo motor as a spindle motor?
My current need is for using it to cut threads on a Sherline Lathe.

do you need to purchase any plugins for this or is it built in?

Thank you for your time.

Have a Sherline here and have cut threads on it using Sherline's spindle motor, threading accuracy was not good enough for myself ( backlash even with the anti backlash nuts installed), good to about 1/4-20.
You will get spindle slow down but the thread cycle reasonably adjusts for it.

I would not recomend a stepper for the motor as it has no torque at higher rpm's and is rpm limited.
Servo should be fine if adequate.

Threading is built into Mach3 Turn, but, the thread cycle will not work if it is unlicensed / trial version.

RICH

How is Spindle speed controlled? PWM ? or some other mechanism?

The true rpm is read and if necessary the feedrate is varied accordingly on the next cycle to adjust the threading.
You set the rpm manualy, so on the Sherline, you turn the rpm adjusting pot to get a desired rpm.
The wizard will generate the required gcode and also check that your velocity and acceleration is adequate for the chosen rpm.

RICH