When I do the 3-axis thing in UGS, then click the ‘Return to Zero’ button. The Z axis lowers until the bit is actually BELOW the top surface of the material and then moves to X/Y zeros as it calculated it using the touch plate. It then drags the bit across the surface on the way to X/Y zero. Arg!!
Why would it lower it further than necessary? Before you ask, YES I have measured my touch plate thickness with calipers multiple times and ensured the numbers are in the script properly.