When Symmetry Is Not Your Friend

When replacing the Z axis motor on the mill, two weird things seemed to break.

1. Z+ used to move the carriage up and Z- used to move the carriage down; now the opposite. 

2. The 8-32x3/8" SHCSs that used to lock the motor to the coupler mount no longer held the motor firmly in place.  It would rotate a few degrees.   Not enough to interfere with operation but still disconcerting. 

It turns out that the motor is almost symmetrical.   I had installed it upside down.  - and + were reversed.  The flanges on the motor that the SHCSs held down were not there so the screws were holding nothing down.  The shaft for the lead screw coupler and the handwheel are identical.  The setscrew in the coupler locks onto the flat where the handwheel is supposed to lock.