Moving in X,Y with deeper Z passes

My machine sat for at least a year. Ran some parts this week and noticed some slight stair stepping on one side of the parts but they were not too bad. Now it’s completely unusable. The first depth pass looks fine, but as it goes deeper it moves -X and +Y. Here’s what is supposed to be a 5/16" hole 0.27" deep and a test 1.5" square with a tab on each side, all with a 1/8" bit.

I can jog the Z up and down all day long against a square in any direction and it’s perfectly square. Certainly it isn’t out by .08" over .25". I have checked all the pulley set screws and they are tight. With the machine powered up the x/z carriage doesn’t move around if I push on it. I retensioned the x and y belts with no change. The z belt is definitely a bit loose but I don’t see how that could cause this. I checked the g code with camotics and there’s nothing wrong with the code.

There’re tight but is one of them positioned against the flat of the stepper motor shaft ?
It’s worth trying the marker trick (draw a line across the pulley and shaft, run that job which fails, come back and check is the mark is still aligned)

The other usual suspect (since you did not mention it?) is a loose v-wheel, go back and inspect every single one of them on X, Y and Z ?

Ah! It was a loose v wheel on the Y2 side. I failed Shapeoko debugging 101! The first pass always seeming to be fine got me fixated on other stuff. Thank you!


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