The octohedron is one of the 5 Platonic solids, which are the 3D shapes that have the exact same shape for each surface.1) Print 12 copies of the file. 2) Glue or acetone the ends together.Step 2 can be a little tricky.I sanded the edges to get them nice and flush. Lots of acetone really helps. If you get the surfaces nice and mushy then small errors in the geometry of your sanding technique won't matter so much. It might help to have a second pair of hands to hold the piece while the acetone is evaporating, but I managed to build this without assistance. The acetone method is pretty forgiving. Don't breathe it in.