This variant of my Z-axis threaded rod locking bearing bracket is coded in OpenSCAD and has captive nut holes in the "top" so it can be mounted upside-down, under the top panel and save you some grief when tightening the retaining bolts.

No wrenches required!

Revision controlled source can be found at: https://github.com/clothbot/makerbot/blob/master/upgrades/z_bracket_simple_nuts.scad

1. Print the calibration part and check the nut hole width, bolt hole width and bearing diameter. Either adjust the OpenSCAD model and re-export the STL or adjust your slicing settings to get your tolerances just right.

2. Print four (4) locking bearing brackets.

3. Insert four M3 nuts in the top. Use an M3 bolt to pull them into their friction-fit position.

2.5 (Optional) Temporarily anchor in position under each corner of the Cupcake's Top and thru the side-wall bolt holes, mark the inside panels. Drill access holes for what will be the hidden set screws.

1. Insert four M3 nuts in the side walls. Use an M3 bolt to pull them into their friction-fit position.

2. Slip a 608 bearing in position and thread four M3 set screws into position on each bracket. Make contact with the bearing surface but don't tighten them until later.

3. Position the bearing brackets under the top panel and thread bolts thru from the top and tighten them up.

4. Slide in the rods and tighten up the nuts that hold them to the 608 bearings.

5. Tighten all the M3 set screws you can access so the bearings don't slide out.