Thursday, May 1, 2014

CNC Mill - demise of another Rotary Tool

Tool Ready for Salvage

Frozen Bearing
In my last post I left off stating that my stepper motors were heating up, squealing and missing steps (what I found was that all this was happening during "Seeking:" movements - fast movements above the surface of the board).

All of this began after I swapped out a few of my stepper motors with ones I purchased for building a 3D Printer (I'll be documenting that build soon).  The newer steppers are also NEMA 17 but are a bit longer - my rational for swapping out the motors was that the new ones should be stronger and better able to handle the weight of the heavier spindle (compared to the weights that a 3D Printer has to deal with - much less).

I approached the issue systematically, looking at possible causes for motor heating, squealing and missed steps:
  • initially thought it must be driver failure
    • testing the the drivers on other motors as well as swapping drivers between steppers in current setup - all drivers seemed fine.
  • poor connections
    • between driver board and arduino - couldn't find any
    • between driver board and motor - nothing
    • between drivers and motor power supply - nothing
  • amperage to high
    • adjusting the current limiting on driver boards
      • this did decrease noise
      • also decreased stepper motor heat
      • Did Not – prevent steppers from freezing up during movements or missing steps
  • step pulse (GRBL firmware settings)
    • I put off testing this until I could look closer at the datasheets for the driver
  • default speeds (GRBL firmware settings)
    • decreasing seek speed seems to have fixed issue
      • decreased to 300 than increased up to 400 and no problems
    • lower current limit seems to be keeping motors (and driver boards) cool
      • 1/8th to ¼ turn clockwise for all motors
    • Other possible answers
      • could be max acceleration instead of max speed