A Pythagorean cup (also known as a Pythagoras cup, a Greedy Cup or a Tantalus cup) is a form of drinking cup which forces its user to imbibe only in moderation. Credited to Pythagoras of Samos, it allows the user to fill the cup with wine up to a certain level. If the user fills the cup only up to that level he may enjoy his drink in peace. If he exhibits gluttony, however, the cup spills its contents out the bottom (the intention being: onto the lap of the immodest drinker).

As you may already know, I wanted a D20 that had "20" on each side. Shamelessly abusing my power as a blogger for MakerBot, I asked the citizens of Thingiverse to create one for me. ( makerbot.com/blog/2011/09/29/openscad-challenge-regular-icosahedron/ ) Polymaker was the first to post a solution and win the prize. ( makerbot.com/blog/2011/09/30/polymaker-dont-mess-with-him-that-dude-rolls-20s/ ) (Though, really prize might be overstating the value...)

I tried printing several icosahedrons at different sizes and resolutions, but none of them seemed to come out very well. Most of the time the extruder would snag the die and pull it off the build platform. Finally I adjusted the design a little in OpenSCAD and printed the D20.

Here's what I did:
1. I used OpenSCAD to scale the D20 down to about 30mm in diameter.
2. I added a thin, 1mm circular disc, 30mm in diameter, underneath the D20.
3. I positioned the die so that it was hovering 0.25mm above the surface of the disc.
4. I printed with support structures on. (But this may not have been necessary)

The big flat disc allowed the die to maintain contact with the build surface and it never came off. And, being placed 0.25mm above the disc allowed the die to pop right off very easily without any sanding or stray threads.

This is a remake of something that my Dad made when I was a kid. His version was made of wood. Its cool because it makes the belt look like it is defeating gravity!