I have a 380-oz-in-nema-23-stepper-motor (380 oz-in NEMA 23 Stepper Motor, 1/4" Shaft | CNCRouterParts) that I use as an A axis motor. I have it slaved and reversed with the Y stepper to control the Y axis. The A axis stepper has a grinding noise as it starts and stops. It also gets hotter than the other two. I've tried adjusting in Mach3's motor control and also on the G540 controller. I also noticed when the G540's ready light switches to red and everything shuts down, it's this stepper that causes the problem. Any suggestions or just a bad stepper?
Do a bit of motor swapping and that'll tell you if it's the motor or something prior like the wiring or the driver. You might also check the resistor at the end of the cable.
The resistors are built into the cables. Ref: CNC Motor Cable | CNCRouterParts The reason I asked is because this sounds similar to something discussed about 2 1/2 years ago. Added Resistors the Z. Sounds like a power issue so time to isolate where it's happening.
