You'll use a fair amount of grinding powder for even a small cut. You need some way to hold the piece of glass firmly in place, and to mount it securely to the table of the drill-press. I made mine from a few scraps of aluminium screwed to a plywood base. The base is held to the table with a G-clamp. I was cutting 1-inch diameter filters from 50mm square Schott filter glass.
Experimentation is the key to success.
The drill press needs to go quite slowly - a few hundred RPM or so. Mine would only slow down to 450 RPM but was still fine for this small cut. I guess the rule is the larger the hole, the slower the speed. Once the board is in place and aligned with the cutter, I set the stop on the drill-press so that it will stop a little above breaking through the glass. Make a dam around the piece so that you can hold a little water around the cutter.