Magic/Rubik's Cube

There are tons of models for Magic/Rubik's Cube on the net. I was interested in trying to model one that is printable with a simple one-color/material printer, can be assembled without glue or additional hardware, and still has decent mechanical behavior.

After having created an initial model I learned a lot of things that you could do wrong. In fact, my first model had tolerances of 0.2mm between the individual pieces since I thought this would improve mechanics but I found that those tolerances add up to so much extra space that the result was way too loose. That combined with some other design faults in the original model led to the situation that while it still worked it could just fall apart while playing with it. As a result, I never published the initial model.

This new model is designed with absolutely no extra tolerances and I found that when printing with PETG this just leads to exactly the right tension in the cube to get a good playing experience. As such this also serves as a good test for the accuracy of your printer. I strongly recommend printing with PETG since the model includes a snapping mechanism for which PLA probably is too brittle. But in the end I didn't try this, so feel free to try it if you like.

My print was done with the PrusaSlicer default settings for 0.2mm layer height (QUALITY) on my MK3S+, meaning 2 perimeters and 15% infill. With similar settings, you should expect good results on other printers as well. Note that the snapping mechanism is designed in a way that the slicer will increase infill on the mechanically critical part automatically without special settings needed in the slicer.

Note that the included pegs for assembling the pieces are very tight and might require players to insert them properly. If you feel this is too cumbersome you might replace them with smaller pegs and compensate for the missing friction by using glue. By doing so you obviously give up one of my purity goals but this decision is up to you.

To get a full cube you simply have to print the included model 6 times, obviously with different colors.

Assembly instructions:

1. Take all the sphere parts and snap them together using the pegs. make sure to assemble the different colors in the orientation you want to have the colors arranged later on the cube. Since the pegs are very tight I found using a screw clamp very useful to press the individual pieces together. At this point refrain from attaching the middle pieces already since you will likely be unable to remove them again without destroying them since the snapping mechanism is very strong.
2. Take three corner pieces and snap them together using the pegs. Make sure to combine the right colors to form a cube with consistent colors. You may use the already assembled center sphere as an orientation. Repeat for each corner of the cube.
3. Take two edge pieces and snap them together using the pegs. Again make sure to combine the right colors. Repeat for each edge.
4. Now start pressing in 5 of the middle pieces into the center sphere. Each middle piece has to go into the hole with the same color. Do not press in the 6th and last middle piece since otherwise, you will be unable to fully assemble the complete puzzle. Again I found it useful to use a screw clamp for pressing the middle pieces in given the strong snapping mechanism. You should take care though not to press it in too deep. You can avoid this by holding an edge piece in the gap since the latch of the edge piece will prevent you from pressing in the middle piece too deep.
5. Insert all the edge and corner pieces starting from the bottom to the top, where the top is the side of the cube with the still missing middle part. Refer to my pictures for reference. The precise order suggested is:
   1. Edge pieces of the bottom layer.
   2. Corner pieces of the bottom layer.
   3. Edge prices of the middle layer. (Note, there are no corner pieces in the middle layer.)
   4. Corner pieces of the top layer.
   5. Edge pieces of the top layer.
6. At this point I suggest testing all the mechanics since this is likely the last point in time you can still correct things without destroying the cube.
7. Finally, press in the last middle part.

I plan to add the OpenSCAD sources to the model later but first need to clean up the code from my experiments a bit. For now, you already get the STL file. Note that for some reason, that I did not yet debug down, OpenSCAD created some non-manifold faces in the model. They do not seem to confuse the slicers though.