My latest fun Z experience was a loose M5 bolt that holds the stationary pulley that drives the Z plate up and down. The symptom was you could move the router up and down by hand with the motor fixed in place.
Anyway, whilst apply my liberal amount of thread lock I noticed that there was no set screw in the pulley. I didn’t put one in since in my humble opinion (was comp.sci. not ME) it wouldn’t help.
Anybody thinking there should be a set screw there? My thinking is if the bolt is loose the set screw isn’t going to do much. Any of you mechanical folks disagree?