This is just something I felt like doing with the bottoms of the Aluminium Red Bull cans I used to make my RedBull Extra 330s Instructable;
For this instructable you will need:
A Red Bull can or just can bottom
Tin Snips or Scissors
Pliers (Preferably long-nosed pliers)
Like 3 minutes...
Step 1: Cut the bottom end off of a can
To cut cans, I use tin snips and basically start cutting from the hole in the top of the can, down the side in front of it, then across around the bottom outer rim. To trim this "cap" to the right size and shape use the same cutting tool to gradually reduce the "lip" to about 3mm from where the bottom-most rim of the can is to the edge.
Further trim this edge so that the circle is even all the way round. This will keep the disk balanced.