Step 3: Build the magnetic top
b) put the neodymium magnet on the cork slice, with the pen trace the internal circle of the magnet on the slice;
c) drill the center of the cork slice with the 5.5mm drill bit. You can do it by hand, the cork is very soft;
d) cut the slice on the line tracked at point b);
e) glue the lateral surface of the slice and then insert it inside the neodymium magnet;
f) shorten the plastic screw (remove both top and tail of the screw with the saw). The final length should be 30mm;
g) reduce the weigth of the screw to 0.7g (use the sandpaper and the saw for that), now youhave all the components;
h) put the screw inside the hole previously made. Finally you have the magnetic top.
i) As I told you in the intro the weight is crucial. At the end of the previous steps the weight of the top should be 15g (more or less). That weight is smaller than you need, for this reason you need to glue one or more washers to the magnetic top. The right number of washers and their weight is well explained in the "Levitation step"