I know your question was about z, but maybe this is a small encouragement: I’ve seen a definite improvement from using manually measured x/y anchor positions instead of the result of the automatic calibration. I then also had to adjust belt tension by scaling the frame measurements very slightly. If you are in for a long read, go ahead, but be aware that it’s still work in progress and I feel like not knowing anything: Feedback on calibration and resulting dimensional accuracy
Oh, and about that Faro scanner: Get rid of it. Throw it my way. (Okay, I admit I’m just a little bit jealous … I can’t even count how often during my home renovation I wished I had such a tool!!!)