When trying to synchronize Z Axis motors, using a set screw on the lead screw can be difficult to obtain a precise set location.
By using this pulley and hub:
The hub can be first fixed to the lead screw using 3 embedded M3 Nuts and grub screws.
The two Z axis motors can be manually moved to level the Y Carriage in its move across the bed.
Power is applied to the motors to get them to lock into detent positions.
The 3 M4 bolts then clamp the adjustable pulley to the hub ensuring an accurate synchronization between the two motors.
Place 2Dshapes.scad and fudge.scad in your library folder.
explains how to use libraries.