I built my Hypercube 300 with a quarter-inch slab of aluminum tooling plate for a bed, but without provision for leveling.  I figured I'd compensate for it with unified bed leveling, but over time, I've ended up with a 1.9 mm difference between the lowest and highest points of the bed.

This is an attempt to correct for that and level out the bed as much as possible so UBL doesn't have to do as much.  It should also improve first-layer quality at the edges.

To assemble, you'll need the following:

• M4x25 screw 
• 4-mm M4 heat-set insert
• M5x8 screw
• M5 T-nut

The bracket has a recess for the M5 screw to hold it to the frame.  The heat-set insert goes into the other hole from what will be the top side (facing the bed).

Since parts of this leveler are in contact or close proximity to the bed, they should be printed in ABS or some other heat-tolerant polymer.  PETG is probably too flexible, and PLA will soften and warp the first time you use it (even if you only print PLA, as the bed temperature will most likely be above PLA's glass-transition temperature).  With a textured PEI print surface and an 8-mm brim, my AM8 was able to print these without warping, even though it's not enclosed.  Setting 5 perimeters will also give the insert something to bite into.  A higher-than-usual infill setting (such as 50%) might also not be a bad idea for a weight-bearing part.

Printed on my AM8 in MG Chemicals red ABS.