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Octahedron & spherical joints

Question asked by Valentine Kunin on Nov 17, 2014
Latest reply on Nov 19, 2014 by Kelef Man

Some materials' atomic structure consists of octahedra, sitting at vertices of simple cubic lattice. Moreover, these octahedra are capable of rotating with respect to each other(at least to some degree) - that is, in some sense they are connected with spherical joints.


I want to 3d print such structure - that is, I want to 3d print a number of octahedra, so that I could connect them to each other (like LEGO constructor), and which would still allow them to rotate with respect to each other (say, up to 15 degrees in any direction).


It doesn't look that difficult - I suppose I should just create an octahedron and to center a small solid ball at any of its vertices. Then I should center another ball at the opposite vertex, and to make it hollow - so that it's inner radius is the same (or slightly larger) as the radius of the first ball, and its outer radius is somewhat greater - say, by 20%. Then I should truncate the second ball by the plane, perpendicular to a line, connecting these two vertices (leaving about 60-65% of the ball). Now if I print two such octahedra I would be able to push one into another, creating a spherical joint:



Then I should repeat it for the rest four vertices (altogether, three solid balls and three hollow ones). I also want to make the octahedron itself hollow (just to save money on 3D printing ), but still rigid enough.


I'm not sure how thick the outer spherical shell should be, and how much it should be truncated, but I'm ready to find out experimentally. Typical size of each octahedron is about 1 cm.


I created a hollow regular octahedron and placed a sphere at one of its vertices (attached). Didn't manage to create the second part of a joint. Can someone please help me do it?