Glass cutting
The method Denis describes is standard practice among optical workers for cutting holes in telescope mirrors, making lens blanks, etc. "Procedures in Experimental Physics" recommends iron or brass tubing, but copper will work also. The main criterion is that it not be hardened because grit embedment is desirable here. The idea is to have the grit stick on the cutter and grind the glass. Notches are normal practice. The book recommends 60 or 90 grit carborundum for thick glass and 120 for fine or fragile pieces, so 100 grit is just about right for this service. It also recommends water but says that you will cut faster with a mixture of one half liter of turpentine and 5 grams of camphor. My own experience is that the cutting edge will wear into a radius, leaving a sharp rim like a burr when it breaks through. The thinner the wall of the tube, the smaller the radius, making a cleaner part. In this case, I would stack several pieces together with the thinnest type of Super Glue, after dropping the glue on clamping them together quickly and firmly to minimize the thickness of the glue layer, and cut through the whole stack. Leaving the stack in acetone overnight should dissolve the Super Glue ( I think, I haven't tried it ). I have attached pictures of a "biscuit cutter" for 2 1/2" holes made from B1113. The spiral lines are just surface rust from the water.
Bill