This is a modified version of a six piece star cube. The original used 6 identical pieces but one that I remembered from my childhood had three different kinds of pieces. My version interlocks much more tightly than the original six identical piece version.
Print one copy of "part 1". Print two copies of "part 2". Print three copies of "part 3".
My part 3 is identical to the original six identical piece version. My parts 1 and 2 were modified from part 3 using Blender 3D.
Visit my blog at http://tech.cyborg5.com/?p=1027 for details on how to assemble if you can't figure it out on your own.