That is great. I got the issue on mine corrected as well. The depth started good but got deeper as it went. I watched it until I figured out the collet on the lead screw was slipping just a little z axis. Got new collet pretty much the same thing. I even flipped the lead screw same thing. The collet just would not hold it without slipping.
I did two things to fix it, which seem to be doing great. The collet was not slipping on the motor shaft just the lead screw end. I could with a pretty good tug pull collet and lead screw apart with the little screw as tight as it would tighten. I took some super glue on the end of the lead screw as pushed it into the collet until bottomed out. Second thing I did,, because the collet and z plate are so close together, tiny gap. I took some electrical tape and wrapped the outside face of the collet, 3 or 4 times around tight. I think it maybe was slipping a little and got worst with time until it just would not hold steady at all. Running like a champ now,

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I hopefully am going to attempt some 3d craving like I see most all of you doing very soon. I was given a load of red oak wood, huge pieces, 5 pieces split in half top to bottom making 10 pieces swats my F-250.

I will cut them all into maybe 3" blocks and let them dry out, plane and shape them up, to carve into them.
You all have a great weekend ,
Ray