Drive Stepper (4th axis) off of PWM Spindle Control Ouput
June 4, 2013
Sorry 'bout this one, I am just sorta "thinking aloud" here, feel free to brainstorm with me, there is no real specific question here.
I want to use the 4th axis (horizontal rotary axis) as a lathe on my CNC. The X,Y,Z would operate normally, the only difference would be that they would be grinding away at a chunk of something spinning, as aposed to sheet-goods clamped down to the table.
This requires me to spin the 4th axis as a "motor" --with no regard to an "indexed" zero-point nor the total number of steps completed. I need set it and forget it, and just keep it spinning. Mach3 has no provision for this.
I occured to me today that the PWM frequency used for the spindle speed control might be what I need to keep my stepper stepping. --I mean, a pulse is a pulse, right? It would just be a matter of putting a scope on the stepper, jogging it as fast as it will go, and taking a look at the pulse rate coming out of Mach. From there, I could do the math required to adjust the PWM frequency and duty cycle to match. -Both of these are very adjustable via Mach3.
Now, for the life of me, I can not figure out why this won't work, but before I start un-wiring things and scoping etc., does anyone have any thoughts?