I used 3/16" aluminum, but you can use 1/4". Mill the inner and outer contours with a 1/4" flat end mill. I used the 2F HSS upcut from Onsrud. Cut a small chamfer on the inner edge. Cut the 3D fillet profile on the outer edge with a ball end mill.
Estimated time: 60 minutes
To do the backside mill a pocket in the waste material to serve as a holding jig. Do a cleanup pass around the edge to remove the tabs. Cut a small chamfer on the inner edge. Route the 3D fillet profile on the outer edge. This removes the burr and makes the edge smooth.
Estimated time: 60 minutes
Install the button cell holders and bearing. Wire the positives and negatives in parallel. Solder the leds to the negative button cell lead. Put the tilt switch from positive to the led positives (I soldered it at a slight angle off horizontal, biased towards off). Spin!
If you don't need leds, 608 bearings will fit perfectly in the space for the button cell holders.