If you have a pet hamster, you know that they like to run in their exercise wheel - a LOT, at NIGHT and often the wheel SQUEAKS. Here is a design for a (hopefully) squeakless hamster wheel that uses a 608 bearing. I don't (yet) have a 3-d printer, so no photos. I made sure there were not non-manifold points.Makerbot - print 4 Quarter Wheel pieces, plain or with ventillation holes. Lay sections to form an entire wheel. Hot glue along the edges. Shove a 608 bearing in the middle hole. Use 4 short m4 bolts and 8 washers to secure 608 bearing into the wheel. Thread m8 bolt through the middle hole (use those washers), through the bars of the cage and fasten with the m8 nut. Use washers as needed to keep the wheel turning freely.Mendel/reprap - print entire wheel at once and continue as above.You can add more holes for ventilation or decoration. I wonder if you could mount tiny, powerfull magnets on the back side of the wheel and try to generate a current through an external wire winding. I think it should be able to light an LED or two...