Z-Axis Stepper Motor Giving Me Fits

Mostly Printed CNC - MPCNC Troubleshooting
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So, I’m in the home stretch of my build, and it’s now all down to the final wiring and testing of my board. While I would have loved to springed for the RAMBO board, my wallet chose the old reliable RAMPS setup, and after a bunch of debugging, I’ve arrived at a crux with the Z-axis. In the firmware, I’ve set up the machine for my T8 leadscrew, with a 2mm pitch, and my NEMA 17 motor with its 1.8 degrees of step angle. With my A4988 steppers, based on many calculators I’ve checked with, that puts my Steps Per MM at 1600 - but when actually applied to the board and tested, I get zero movement from the motor (but when using my standard X/Y setting of 100 SPMM, movement is achieved).

I’m probably overlooking something basic and silly, but it’s late and I’ve probably sniffed a little too much solder today. :wink: Anyone else run into this?

BTW - I absolutely LOVE this thing!!!

Thanks In Advance!

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Most lead screws for this purpose are 2mm pitch but 4 starts, so 8 mm advance per revolution of the leadscrew. With 1/16 microstepping you have 16 microsteps * 200 steps per revolution = 8 mm advance, or 400 steps per mm, not 1600.

If your lead screw has only one start, then your number is correct, and in that case the next most likely problem is z speeds too high. The motor can only turn so fast amd you have to keep the z speeds way down (even lower than normal) if you have only one start on your lead screw.

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