Print, de-fuzz. Place the perforated tab of each spring into the respective slot on the main body. Retain with an M4x40 bolt and nut (no washer). The two semi-circular rail guides face away from the nut trap.

The interface assembly opposite the motor will require pulleys to guide the belt. In each of the two solid corners, fit an M4x40 with washer and captive M4 nut. Fit two wide M4 washers, 6 narrow M4 washers, one more wide M4 washer and an M4 nylok nut to form the pulleys.Do not fully tighten the nut; allow the washers to rotate freely.

For assemblies on either end of the X axis fit screws to the clamps. In the two remaining holes insert an M4x40 screw with washer and a retained nut. Do not fully tighten until it is on the X axis rails. Ensure the threaded rod and smooth rod on the Z axes are as parallel as possible to reduce friction.

Before threading the assembly onto the Z axis drive rod (rail guides facing the rail) pinch two M8 nuts into the nut trap so that the plastic springs therein are lightly compressed to provide anti-backlash.

When first used, the threaded rods will be relatively stiff to move. This is particularly true of zinc-plated threads. Add a little oil and run the Z axis up and down a few times first to wear it in. Worst case, you may have to point a fan at the Z axis motor to cool it down during the wearing in period.

The mendel_misc.inc file is found here:
thingiverse.com/thing:2192