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A Rubik's cube with patterned faces distinguishable by touch, so it can be solved by a blind or blindfolded person.
It is fully 3D printable, requiring no screws or springs.
More detailed instructions and pictures here:
Parts to print:
UPDATE (22/07/2011): I put all the pieces together in 6 plates, so you can print one of each plate if you want ;)
1 corner with each pattern (8 in total; corners are printed at once)
1 edge outer part with each pattern (12 in total; each edge outer part will be glued to an edge inner part)
12 edge inner parts (all the same)
1 center outer part with each pattern (6 in total; each center outer part will be combined with a center inner part and a center core)
6 center inner parts (all the same)
6 center core parts (all the same)
The cube has the following 6 patterns on its faces: dots, stripes, plain, pyramid, circle and hole.
Start by printing the corners, they are already properly patterned, so just print one of each and you're done with the corners.
Then let's print the edges. Because of the patters, I couldn't find a way to print the edges at once like with the corners, so each edge is printed in two pieces. Print one of each edge outer piece, each one has 2 face patterns on them. Then print 12 edge inner parts. Now glue each inner and outer part, and you got your edges. (I suggest you sand with a rough sandpaper each surface which will be glued, so they adhere better)
At this point I placed all my edges and corners on my C4U's core to see if everything was ok. I checked the patterns and the way the pieces fit together. Now you'll want to sand the parts of the pieces that touch each other so you can make the cube move more smoothly. They probably won't get perfect, so be careful how much you are sanding or you might open holes on your pieces.
Now to the centers. Each center piece is printed in 3 parts - outer, inner and core. Only the outer has patterns, so each one of the 6 outer centers will be different. Then print 6 center_inners and 6 center_cores. Not to need screws, this cube rotates with a cone inside a chamber. the chamber is formed by the inner and outer parts. Before assembling the centers, sand the surfaces which will touch others, especially the inside walls of the hole on the inner part and the (head) of the core so they slide better against each other.
To put each center together, you will put the core through the inner part (it only enter right one way) and glue the outer part on top of the inner part trapping the core inside the chamber. Be careful not to glue the core to the other parts, or it won't rotate. If you did it for all 6 centers and they are rotating, you are almost there!
The core is simply a little cube where all 6 centers will be glued to. Be very careful with the core, it is tiny and the makerbot's resolution doesn't make a cube as even as desired (for me at least). You'll want it to be as even as possible, so your cube rotates well (mine was initially bent and one of the faces didn't rotate nicely). First, to check if everything is ok, glue two adjacent centers (make sure they go along the whole cube's pattern arrangement) to the core as in the picture and try to fit an edge through them. If it enters without effort and gets trapped by the center caps, your cube is doing well. Glue all the other centers to the core, being careful with the arrangement of the patterns (check the corners and edges for that, and make sure pyramid is the opposite to stripes, hole is the opposite to plain and circle is the opposite to dots).
Now you just assemble the cube like in a regular Rubik's cube. for those who don't know how to, you can easily find a quick tutorial on youtube.
And now you got your fully printed patterned cube!