how to cut glass circles
Start with a sheet of glass as close to the size of the circle you want to make as possible. The less extra glass you have to remove (to a point, at least), the simpler the process will be.
Draw a circle pattern on paper by using a compass or tracing a circular object. Cut the circle out and use rubber cement to attach it to your glass sheet.
Trace right around your pattern, using a glass cutter
to score a circle into the glass.
Score several gently curving lines connecting portions of the circle to the edges of your glass sheet. Another way to think about this step is scoring around the extra pieces of glass that you must remove one by one.
Use the running pliers to squeeze the edge of the glass where one of these score lines ends. Squeeze gradually until you hear a crack, which should be along the scored line. If no glass comes off, repeat with the other scores. Repeat until almost all the extra glass has been removed, making additional score lines if necessary.
Use the grozing pliers to trim small rough edges from your final piece, forming cut glass circles that are close to perfect.
Clean up the glass circle, removing the paper and rubber cement and grinding the cut edges smooth if you like.