How to Drill Glass: Bottles, Mirrors and Glass Sheets

Drill ordinary glass with a diamond core bit or a carbide spear-point glass bit, at slow speed with light pressure and with water on the hole the whole time. Support the glass fully from underneath, start the hole at a slight angle or through a guide so the bit does not skate, and ease off as it breaks through. This only works on annealed glass: tempered glass can’t be drilled because it shatters.

Which bit for glass?

Bit	Best for	Notes
Carbide spear-point	Thin glass, small holes, mirrors	Cheaper, slower, can chip the exit side
Diamond core bit (hollow)	Bottles, thick glass, larger holes	Cleanest result, always used wet
Diamond-tipped solid bit	Small holes in glass and tile	Used wet, light pressure

For thin glass and small holes a spear-point bit is enough. For thick glass, bottles or holes bigger than about 1/4 in (6 mm), a diamond bit is the safer choice. The same diamond bits are used for porcelain tile.

How to drill a hole in glass

1. Check the glass. Tempered glass often has a small etched mark in one corner. If you can’t tell, treat it as tempered and don’t drill it.
2. Lay the glass flat on a firm surface, such as a sheet of plywood or a folded towel on a bench, so no part hangs unsupported.
3. Mark the hole on a piece of masking tape. The tape keeps the bit from skating.
4. Build a dam of plumber’s putty or modeling clay around the mark and fill it with water. A drip bottle or spray bottle also works.
5. Start with the drill tilted a little so the edge of a core bit cuts a crescent, then bring it upright. A drilling guide with a hole in it holds the bit in place without tilting.
6. Drill at the slowest speed that keeps the bit turning, with hammer mode off. Use light pressure and lift the bit now and then so water gets underneath.
7. On thick glass, drill from one side until the hole is about halfway, then turn the glass over and finish from the other face. On thin glass, ease off as the bit breaks through.

Drilling a bottle or a mirror

A bottle must be fully supported and kept wet, because heat and uneven support crack it. Drill it while it sits in a shallow container of water, or build a putty dam on its surface. A mirror is drilled from the glass side, not the silvered back, so the coating does not tear. Go slowly and keep the hole wet.

Mistakes that crack glass

• Dry drilling. Heat builds up and cracks the glass.
• Too much speed or pressure, particularly at breakthrough.
• Drilling too close to an edge or another hole.
• Using hammer mode.
• Drilling tempered glass without knowing it. Glass in shower doors, side windows of cars and many table tops is usually tempered.

Safety

Wear safety glasses and gloves, and a dust mask if the ground glass dries into powder. Clean up splinters with a damp cloth, not bare hands.