Stepper motor as spindle in CNC mode

  • Hello,

    is it possible to control a stepper motor as spindle in cnc mode instead of a servo drive?

    My goal is to control the stepper velocity instead of its position (as it is in normal 3d printer mode).
    E.g.: Move (endlessly until the next command) clockwise at 200 rotations per minute -> Move (endlessly until the next command) counterclockwise at 10 rotations per minute etc.

    Kind regards

  • administrators

    There is currently no firmware support for that.

    I think it would be difficult to get the speed and torque needed for a CNC spindle from a stepper motor.

  • That and it could take a chunk out of your max step rate for the other motors

  • AT 200 RPM you should be ok with the stepper, but I'd question the torque even if the firwmare was able (which its not as dc42 points out)

    I'd hook an external diver up to an arduino/esp32 and drive the stepper with either reading the pwm and direction from the duet or by sending uart commands to the paneldue port.

    What you planning on "spindling" and what stepper motor you got in mind?

  • I was playing with this for a lathe and did not find a proper solution with stepper

    • using a stepper shown to be crap for the spindle, I even tried large nema34 16A ones... the torque & speed are just not acceptable, even with FPGA stepper (mesa card and linuxcnc, so I was easily stepping at 2MHz but it's just not something stepper deals with)
    • using encoder and servo worked great on linuxcnc + mesa but I never managed to reproduce this on any of the 32bit boards (rrf, redeem, smoothie..), especially as there's no way to push encoder data back into them... also stepping speed on all of them is too slow for high precision encoder on the servo ..

    I do have a small mill where I use smoothieware (RRF would work even better maybe) where I control the spindle by SPI, I have a small pic that listen to SPI and it gets the speed for the spindle from SPI from the firmware and then it converts it to 1-10V input for the VFD ... (I lost that firmware for the pic 😞 but it's a 30min job to write for any mcu, I need to write it again I need another one for a bit different mini mill I have)

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