7U end cheeks for Tiptop Audio Z-Rails

Requires 3 pairs of Tiptop Audio Z-Rails and twelve M4 screws with washers (O.D. ≤ 9.5mm).  The 1U row is Intellijel format.

Recommended assembly method:

1. Remove support material from each screw recess.  (The recesses allow the show surfaces to have a build plate texture.)
2. Awkwardly screw all six Z-Rails into one end, not fully tightened.
3. Place that end down on a table and screw the other end into the rails from above.
4. Insert a few modules (preferably with 4 screws and wide, factory-made panels) to align the rails accurately.  Do this at/near the ends to avoid parallelogram-ization.
5. Tighten the end screws.  Don't deform the plastic by over-tightening.  The washers will help prevent this.
6. Always pick your assembled rack up by both ends.  I'm not sure if these are strong enough to pick up by one back corner, and you also don't want to pick it up partially by a module's exposed circuit board.

Tested with PLA silk filament and works.

Module depth limit:  40mm ("skiff-friendly" modules) in the top and bottom rows, and 70mm for the middle row.

Since the case has no back or bottom as shown, modules may end up sitting on cables run behind the panel.