I printed at 2mm layer height w/25% fill and 3 shells: the post needs to be strong enough to endure sanding and dropping off of tables and such to the floor. To assemble get some silly putty and a nickel. Sand the bottom of the spherical piece and the post really smooth. These are the parts that the top spins on and too much friction inhibits a good spin. Sand away the imperfections on the outside of the cylinder and the inside of the spherical piece that it slots into. Does not have to be smooth, rough works best, but enough so that the cylinder will slot into the sphere. Don't slot it in until the top is weighted /w the nickel. After sanding press the putty flat (I use a plastic lid) and use the spherical piece to cut out a disc of putty. Press the nickel into the disc. Drop the putty/nickel, putty side down into the spherical piece. Press on the nickel firmly. Slide the cylindrical piece into the spherical piece. Spin it like a standard top. If you get a good spin on a smooth surface it should tip over and spin on the post. Then read about physics to figure out how it works. The stl file contains both pieces of the top. My practice is to do a print whenever I switch colors until I get three and then make 3 2-color tops. Video of two tippy tops tipping: https://www.facebook.com/video.php?v=989043771108304&pnref=story