Over the next several posts here I'll put up pictures and files of the objects in the set of polyhedral models I made for the Makerbot Academy Math Manipulative Challenge. Back on Day 63 I tried to make a folding net for a tetrahedron with hinges in a center-cylinder-surrounded-by-open-cylinder design. The cylinder design turned out to be unreliable and finicky so I made new hinges based on cones and cone-shaped holes, and added some snaps to the border edges. Here's the new hinged tetrahedron:
STL file: http://www.geekhaus.com/makerhome/day80_tetrahedron.jpg
Tinkercad link: https://tinkercad.com/things/40G0KzRmvFC-hinged-tetrahedron
Thingiverse link: http://www.thingiverse.com/thing:185859
Settings: Makerware .3mm/low in 35 minutes on a Replicator 2. The entire model prints in one flat hinged piece with no raft or supports, ready to fold up and snap together as soon as you remove it from the build platform.
Technical notes: It took a lot of fiddling to get the snaps to be the correct size. If you want to change them to be tighter or looser, you can edit the model on Tinkercad before printing. The simple tetrahedron does a good job of staying together regardless of how loose the snaps are, but for more complicated objects with wider angles, the snap width becomes crucial.
Special thanks: Alexis Stevens came up with the idea of making polyhedral nets for K-12 educational models and helped with hinge/construction discussions that led to the way that these models were constructed. Thank you Alexis!