By sawing out a round board, laying it flat on a sheet of glass and running your glass cutter around the edge of the pattern you can cut out an approximately round disk of glass.
Fig. 86. A Circular Glass Cutter
But to cut out a perfectly round disk you must have a circular glass cutter 93 as shown in Fig. 86. It has an adjustable cutter head mounted on a square rod so that the head can be turned on it. The rod is mounted on a hardwood base so that it can revolve around the latter.
After the cutter head is set on the rod for the size of the circle you intend to cut hold it down on the glass by the thumb-piece. The cutter head is then moved round in a circle and a clean cut is made after which the edge of the disk can be smoothed up.
This circular glass cutter, which is called the Little Beauty, will cut a circle 20 inches in diameter and costs about 50 cents. If you are making a fric-tional electric machine this is the tool you need to cut the glass plates with.