[ninefinger]

I have an EMCO Compact 5 that I'm converting to modern CNC controls with new stepper motors and drives. At the same time I'd like to take control of the spindle with the CNC controller as well. The original machine has a spindle on/off switch (white rocker switch in photos) and a variable pot to control the speed with a slotted disk and optical sensor updating a display with the spindle speed (ie there is no closed loop feedback, just the display for the operator to react to).

I am planing on changing out the rocker switch with a SSR - that is the easy one.
My big question is how can I replace the variable potentiometer with something controlled by the CNC controller (Machinekit or LinuxCNC)?
Do I just use a MOSFET and pulse width modulate it? Is there a better way?
The pot is 50K and is seeing 7.6 VDC in (seems to be a linear pot).
I feel like I need to somehow isolate the DC motor control voltage from the PC...
Other potentially useful info - I'm using 24 VDC (ie have available) to drive the steppers (Nema 23 for X and Z and a Nema 17 for the tool changer).

Note - I really want to reuse the existing motor and motor power supply as they are there, working fine and designed for the machine so suggestions to replace with a VFD, treadmill motor / controller etc are not what I'm looking for at this time.

Help is appreciated - electronics are not my strong suit but I get by...

Thanks,
Mike


finally the whole machine as it sits today..

[CS900]

https://cnc4pc.com/c6-variable-speed-control-board.html

that should do you. and it already has forward and reverse relays built in.

awesome little lathe BTW. I'm very jealous of the little tool changer!

[ninefinger]

Thanks for the link, I didn't realize that the analog output could replace a pot, I always thought they were just for input to a VFD. I'll check and see if the $10 BOB I have that outputs 0-10V will work, if not I might end up buying that.
Mike