Hi,
I have a speed sensor on the lathe already for threading. Does Mach 3 read this speed input and then decide what output to send to the motor controller?
That depends on your motion controller. Mach's parallel port, despite being run in the same PC as the Mach application, is
a motion controller, and can vary its PWM under certain circumstances. There are other external controllers where that is not
the case. Indeed Mach3 always, historically, used to be an 'open loop controller', that is without feedback control.
The attached pic is from Config/Ports and Pins/Spindle Setup. I have never used this particular feature of Mach3, in fact I use
Mach4 now and wont be going back either, but I understand that Machs parallel port requires an index signal from the
spindle, that is one pulse per revolution. The PID control then adjusts the PWM signal to suit the commanded spindle speed.
Note that the control loop is pretty slow, it cannot accommodate rapid excursions in speed but is none the less an advance
on open loop control.
The Chinese motor controller has the three connections for a 10k pot for the speed control. Its plausible I can plumb my PWM converter into these connections to control the speed?
Yes it is plausible but it is not a slam dunk either. Some US made KB DC controllers can and do work that way, but not all.
The DC motor has CW written on it. I thought all DC motors were reversible? Wondering if this one is reversible or is there something mechanical that would make it unhappy going in the other direction
You are correct most DC motors are reversible. It depends on the phasing of the brushes on the commutator.
If the brushes are neutrally phased then the motor can run either way. If however you set the brushes a few degrees off neutral
then the motor will work much better one way than the other. It will still run backwards probably but you will likely
reduce the life of the brushes and/or wreck the commutator. It might be that you can adjust the position of the brushes
inside the motor. I personally am not familiar with the process. I have fiddled with and old school DC generator that had
adjustable brushes and you could tell it had a 'sweet spot', not very scientific but it worked.
Craig