Stepper motors going in opposite directions after tool change

Hello all,
The weirdest thing just happened to me. I’ve had my Primo build for about 18 months now, and it gets used a couple of times a month. Recently it has started to get used more. For the most part what we do is basic cutting of parts. As such, we don’t have a lot of tool changes. For the most part the 1/8" endmill does was we need.
Tonight I decided to try something different – essentially try to make a small series of bowl shaped indentations into the piece. This involved a tool change for a ball ended bit.
The first part of the cut went as expected. I jogged the toolhead to where I wanted to start from. I started the cut, and after Z was probed, it went for it and started cutting.
Then comes the tool change. I’ve got a Dewalt 660, so the tool change isn’t super easy, but after the endmill cooled down, I got the tool changed. I resumed, which reprobed Z, and resumed again. The tool started and went to move to position.
As I was watching, something seemed off, the position wasn’t where it was supposed to be. Watching it for a few minutes longer, I could see that the 2 X stepper motors were turning in opposite directions. Not cool.
What’s really weird is why this happened after the tool change. And now it is persisting after a reboot.
Anyone have any thoughs?

I have a Primo with dual stepper motors on X and Y, powered by an SKR Turbo 1.4 with TMC2209 drivers, if any of that matters.
And here is the tool change GCode I have in Estlcam:

G0 Z35 F500 ; Raise Z axis 35mm
M107 ; PID, Stop spindle
M00 ; Wait for LCD button press
;Change tool: <n>
G28 Z ; Home Z w/ Z-probe
G92 Z0.5 ; Account for probe thickness (set your thickness)
G00 Z5.0000 F500 ; Raise Z probe off off of surface
M00 ; pause for LCD button press
;M03 S<s> ; PID, set spindle speed
M106 ; Start spindle

Could this be a bad stepper motor that is just wreaking havoc?

LOL - one of those shop gremlins must have appeared in the middle of the night and reversed the x axis driver connector on your MPCNC. Would suggest unplugging the x axis driver connector at the control board, rotate 180 degrees and plug it back in. Bastards!

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Are you sure they moved in opposite directions? If one side stopped working, then it might appear they were moving in opposite directions as one side slid back and forth and the opposite side just moved slightly. If one side stopped, look at the grub screws in the pulley for that stepper. An intermittent wiring issue could also cause one side to not work. Changing the bit might stress either the pulley or the wiring.


I’m 100% certain that this isn’t the issue because I watched the entire first part of the cut, and aside from the tool, nothing changed.

I am not in fact sure, now that you mention it. I’ll have a look at this this evening to see.

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Could it be the grub screw gremlin?


I finally made it back to this, and it’s still a bit of a mystery.

All of the grub screws are tight, and both steppers seem to be turning as they should, aside from the fact that Y2 is turning anti-clockwise when it should be turning clockwise.

I did turn around the Y2 connector at the board, and as one would expect, everything is working normally.

I just can’t figure out why Y2 decided to switch directions, and how I might prevent it from happening in the future.

Tomorrow (I hope), I’m going to grab a new piece of stock and try the same cut again just to see if the same thing happens again after the tool change.

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