There are a number of methods to avoid chipping out the back of the glass when drilling:
- Placing a piece of scrap glass under your good glass will help avoid chipping on the backside. By pressing firmly but gently on the glass (not the bit) the bit will go through the upper piece of glass without chipping the back. This can be a difficult process to keep stable when both the pieces of glass are wet.
- Another method is to put duct tape under the glass to help minimise chip out.
Drill from both sides to avoid chip out as the bit breaks through. Go slowly toward the bottom of the hole. When the hole is almost through, turn the glass over and drill back to front.
- Sometimes the glass is curved and drilling from the back is not easy. This is when the drill press mechanism to stop the bit comes into its own. Before switching the drill on, lower it to the surface supporting the glass. You can adjust the mechanism to stop the press just as it reaches the support surface. Then place the glass under the press and the turn the drill on to begin the drilling.
- Don't push hard as you come to the end. Don't push down any harder on the drill press levers than you comfortably can with the tips of your fingers throughout the process. Keep it steady. Listen for the sound of diamond grinding glass.
All these things will help to avoid chipping out the glass at the bottom of the hole.
Keeping things wet
Using a drill press
Drilling with a Flushing Head
Drilling holes with copper tube and grit
Drilling glass without a drill press
Drilling speeds for diamond bits