@AlexW good advice, thanks. I did take it apart, and I found two issues with the lead screw. Appreciate it if you and others can chime in and say if they have seen different or similar things on their machines.
- There is interference between the plastic collar on the anti backlash nut on the Z axis lead screw and the spindle mount. See picture below. This interference is putting a bend on the lead screw. Seems possible this is the cause of my original issue, documented here.
- In free air, attached to nothing, the anti backlash nut is so tight on the Z axis lead screw that I can’t even turn it by hand.