This design is a slight modification of owens' support-free Menger sponge, with the base sliced off slightly to lie flat on the build platform. (Else a tiny corner sticks down in the center and prints on a tiny layer by itself, making the rest of the model too high off the build platform to be stable.) Used for a printer test of an Afinia H-Series printer with PLA, a MakerBot Mini, an Afinia H-Series printer with ABS, and a MakerBot Replicator 2, shown in that order in the figure above. MakerHome, Day 356: http://makerhome.blogspot.com/2014/08/day-356-menger-testing.html