Design for magical spherical dice (3D printed)

I designed a die. It’s special because it’s a sphere pretending to have six sides: each roll will end with one to six dots facing up. It’s also special because you can print a copy. The trick is a weight that falls into one of six pockets under each of the numbers. “Spherical dice” sounds better than “spherical die,” so print two.

Some assembly is required: You just have to drop in the weight and jam in the plug. According to the colleague that helped me, Nobuyuki Umetani, fishing stores are the best place to get lead. For the plug, you can use your thumb. Most of the plug will still be sticking out post-jam and you’ll have to snap off the rest. The way many printers print makes them snap clean along the path of the printer head. So score the plug by drawing a knife around it’s diameter where it meets the sphere, steady it (with a vice or on the edge of a table), and give it a good whack.

Notes

  • The roll has satisfying action. Video at bottom.
  • The plug is tapered so as to jam well. It functions as the number one.
  • With this design, the strength of the jam may influence the fairness of the die. Probably not a real concern (since the ball’s mid-air choice of pockets will have a bigger influence on the outcome), but this is an imperfection in the design. Someone will have to do a few thousand or so rolls to make sure.
  • The density of the fill and the weight of the missing dots could also influence a die’s fairness, but if you care that much then you know not to bet six with any dice that didn’t come through a casino.
  • You can fill the dots in if you want them to stand out. Nail polish will do. Just be careful: the plastic doesn’t forgive mistakes because its layers act like capillaries and suck up liquidy paint (or nail polish removered nail polish)
  • You want the diameter of the lead weight to leave some wiggle in the pockets. If your weight is a snug fit into the die, get a smaller weight (or scale up the size of the model).
  • I’ve oriented the model at an angle so that it’ll print correctly (without any support material on the inside) if your printer can handle printing a 45° overhang. It probably can? I don’t know how common that is, but the machine I used can.
  • The original design subtracted an octahedron from the center of the sphere, but it was a little too sensitive, and also harder to make fair, so I redesigned it to subtract three mutually orthogonal boxes.
  • Workflow was 123D (for the orthogonal part) to Meshmixer (to sculpt out the dots) to MakerWare (staging and path planning) to a second generation Replicator.
  • I got the idea from someone who did the same thing in wood. I saw it for sale at a store call Aha.

And, this is how I roll: