Downward drift Z

[Jonathon]

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.

[Jonathon]

[WillAdams (William Adams (Carbide 3D))]

Which machine do you have? Which Z-axis?

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

[mhotchin (Michael Hotchin)]

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?

[SLCJedi (Josh Tenny)]

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