Downward drift Z

Stumped on this one. Any suggestions? Using Vcarve Aspire, exporting to correct machine type. Using Carbide Motion to run Shapeoko 5 Pro (2x4).

Simple pocket. Everything starts fine, but later in run, the Z-axis will begin to drift downward, cutting deeper than designed. See fine steps downward near outside edge of pocket.

No loose bolts. Z is zeroed correctly. This happened on several pieces initially, until I quit using Bitsetter. It stopped, now it is occurring again.

Been in CNC for five years and never happened on my old machine (Bob’s CNC).

Any suggestions greatly appreciated.

Which machine do you have? Which Z-axis?

Is there a retract? Could something be interfering mechanically when retracting?

Mark where the bit meets the collet, make sure the bit isn’t being pulled down out of the collet.

Could the wood be flexing or warping as you cut it?

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Have you lubricated your linear rails/bearings lately? The added friction of dry bearings can cause a lot of weird issues.

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