Drilling into tempered glass requires special diamond drill bits in order to cut through the dense glass. The procedure can be long depending on the thickness of the glass, and the drill bit needs constant lubrication in order to make it through the glass. Certain glass and drill bits require different drill speeds in the drilling technique.
Loosen the grip on the drill for the diamond bit installation. Insert the diamond bit into the opening. Tighten the grip on the diamond bit. Adjust the speed on the drill: 800rpm if the bit is half an inch long, 500rpm if the bit is an inch long, 250rpm if the bit is 2 inches long, 160rpm if the bit is 3 inches long and 125rpm if the bit is 4 inches long.
Clamp the glass down with the C-clamps. Buffer the area between the glass and the clamp with the rubber. Position the glass under the drill or position the drill on the glass where you want to drill. Double check the speed of the drill.
Make a thick border of clay an inch away from, and completely surrounding, the drill area. Begin drilling. Keep the area you are drilling into moist at all times with water to lubricate the drilling. Spray water with a squirt bottle into the dammed-in area; if you keep the bit well lubricated you prevent fracturing the glass or reducing the life of the bit.