Slave axis not in sync with primary axis

Problem: After a long XY cut the slave (A axis) is out of sync with the primary Y axis. Primary axis returns to the 6 o’clock position where slave axis is 1 to 2 revolutions CCW from 6 o’clock position. This skews the Y axis.

Method: center cutter in work and mark the position of the both stepper pulleys (sharpie at 6 o’clock) then return to start position after the cut. The cut is about 10 min long. Inaccuracy grows over time.

Machine: two stepper Y axis. G540 UC100. Mach4 on win10 pc. Stepper belt drives an acme lead screw.

Other: Due to two dead inputs on the G540 I cannot home the machine. I square machine (X and A same distance from home) and zero DRO’s. Motor setting are identical Y & A.

I swapped the motor leads Y to A and the problem follows. I.E. the inaccuracy now shows up in the new slave axis. So the issue is not in mechanicals, pulleys, stepper leads, steppers, G540 channel, and UC100.

Any thoughts?


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It sounds like you need to fix your G540; Gecko is usually pretty good about doing that.