Micromill - Z Axis Not Holding Offset

[Benny]

Customer writes – Each morning when trying to make the 1st cut of the day, the mill makes twice the depth of cut. It sounds like the bit is going to break. Then, I re-home the machine and try to make another cut and the bit doesn’t touch the plastic. Usually after, I re-home the machine about 4-5 times it makes the proper cut. I think the Z is just not holding offsets until re-homing several times. Any suggestions?

[Benny]

Possible binding in Z axis. The spindle head may be binding when it goes up on the Z axis. Check spindle head for tightness and lubricate with a light grease (NOT WD -40). Lightly lube the slide ways and the lead screw with a light grease (Moly Grease is fine).
Check the gib strip, that it is not set too tight. It should be snug enough to take out any side-to-side play in the spindle head/column assembly, but not so tight that the stepper motor stalls when bringing the spindle head back up the column.
Check the Z home switch. Check for any loose connections or cracked wires at the switch. Clean the switch, vacuum out around the switch and blow it out with compressed air. Check the bolts holding the switch and the pushrod on the spindle head that pushes up against the switch, make sure everything is tight.
Another related article on the forum:
viewtopic.php?t=1192&highlight=micromill+2000++axis