@Rorgaard I'm glad you got it working. I have a few comments:
@Rorgaard said in CoreXY sometimes homes correctly, sometimes does its own thing:
I lowered the acceleration by a factor of 10. I may increase it again later but for now things are working.
Recent versions of RRF have a command M201.1 which allows you to set a lower than normal acceleration for stall homing moves and Z prove moves. This helps to avoid getting a stall when the homing move starts, caused by extra load as the motor accelerates the mass of the print head.
@Rorgaard said in CoreXY sometimes homes correctly, sometimes does its own thing:
I increased the x/y homing speed to F6000. at 3600 it kept grinding on the stop.
There is a minimum speed at which stall detection is activated, set by the M915 H parameter, because stall detection at low speeds is not reliable. See https://docs.duet3d.com/en/User_manual/Reference/Gcodes#m915-configure-motor-stall-detection. At F3600 you may have been below that speed.
@Rorgaard said in CoreXY sometimes homes correctly, sometimes does its own thing:
I got rid of the repeat of the home. Once is good enough anyway, no need to do it twice.
That's fine if it reliably detects a stall when the physical endstop is reached and not before. Bear in mind that when the motor is hot, stall detection sensitivity increases.