Hi,
My understanding when i bought them was that they were not a true servo but a stepper motor with encoder feedback into the driver.
That is essentially correct. You don't need, or indeed want, any other encoder. The PMDX-416 only has five inputs. You do not
have spare inputs for things like encoders, in fact you don't really have enough for home and limit switches as is. You will also
need an Estop and a probe, so there is two of the five available gone.
You may want to consider the PMDX-416's bigger brother like the PMDX-424 as it has a few more inputs or if you want
more still inputs an ESS, or UC300, or 57CNC.
The important point is that Mach and the PMDX-416 will issue pulses to the stepper drive to travel 1 inch say, and
the stepper drive will ensure, barring overload or other fault, that the axis gets there. You can program the drive such that
should the stepper fail to stay in sync with Machs planned trajectory the drive will issue a 'following error' fault.
To do lathe threading you will need an index signal on the spindle..
Craig