Yes, you can drill a hole in glass at home without cracking it — but only if you use the correct equipment, take your time, and keep the glass cool throughout the process. Rush it or use the wrong bit, and you'll almost certainly end up with a crack or a shattered pane. Here's what you need to know before you start.
What Type of Glass Can You Drill?
Not all glass is safe — or even possible — to drill through at home.
- Annealed (float) glass — standard window glass — can be drilled carefully by a confident DIYer.
- Laminated glass can sometimes be drilled, but it's tricky and the interlayer can cause problems.
- Tempered (toughened) or heat-strengthened glass — cannot be drilled. Attempting to drill tempered glass will cause it to shatter instantly into small pieces. Tempered glass is used in shower screens, sliding doors, some oven doors, and safety-glazed windows. If you're unsure what type of glass you have, check with a qualified glazier before attempting anything.
Under the NZ Building Code, safety glazing requirements mean certain locations must use tempered or laminated glass — check the relevant Building Code clause with your council or a qualified glazier. Never assume — always check first.
Tools and Materials You'll Need
- Diamond-tipped or carbide-tipped glass drill bit (not a standard twist bit — these will crack the glass)
- A variable-speed power drill or drill press
- Masking tape
- Plasticine, putty, or a purpose-made water dam (to hold cooling water)
- Cold water
- Safety glasses and gloves
- A stable, padded work surface (old carpet or foam works well)
Diamond-tipped core bits give the cleanest results and are available at Bunnings or Mitre 10 in a range of sizes. Choose a bit that matches your required hole diameter.
Step-by-Step: How to Drill Glass Safely
1. Prepare Your Work Surface
Lay the glass flat on a padded, stable surface. Never try to drill glass that is vertical or unsupported — vibration will cause cracking.
2. Mark and Tape the Spot
Apply a piece of masking tape over the drill location. Mark your centre point on the tape with a marker. The tape helps prevent the bit from skating across the surface when you start.
3. Build a Water Dam
Roll a small ring of plasticine or putty around the drill point to create a shallow well. Fill it with cold water. This is critical — heat is the enemy of glass drilling. Without cooling water, friction will cause the glass to crack.
4. Set Your Drill Speed
Use a low speed — generally no more than 400–600 RPM for smaller holes. High speed generates heat and vibration, both of which cause cracking. If your drill has a speed dial, start at the lowest setting.
5. Start Drilling at an Angle
Begin drilling at a slight angle (around 45°) to create a small notch, then gradually bring the drill upright to vertical. This stops the bit from skating. Apply gentle, consistent pressure — let the bit do the work. Never force it.
6. Keep It Wet and Go Slowly
Top up the water dam regularly. Drill in short bursts of 10–15 seconds, lifting the bit to let water flow back under it. You'll see a fine glass slurry forming — that's normal.
7. Ease Off Near the Breakthrough
As you get close to breaking through, reduce pressure significantly. The final breakthrough is where most chips and cracks occur. Some tradespeople flip the glass and drill from the other side for the last few millimetres to get a cleaner edge on both faces.
8. Clean Up Carefully
Glass slurry and dust are hazardous. Rinse the area thoroughly, and dispose of waste carefully. WorkSafe NZ recommends treating glass dust as a respiratory hazard — wear a dust mask if dry grinding or sanding edges afterwards.
Common Mistakes to Avoid
| Mistake | Why It Causes Problems |
|---|---|
| Using a standard twist bit | Wrong geometry — will crack or chip glass immediately |
| Drilling at high speed | Generates heat, causes thermal cracking |
| No cooling water | Friction heat builds up and shatters the glass |
| Too much pressure | Vibration and stress fractures |
| Drilling tempered glass | Glass will shatter — no exceptions |
| Drilling unsupported glass | Flexing causes cracks |
Safety First
Always wear safety glasses and cut-resistant gloves when working with glass. Even a small chip can cause a serious eye injury. Keep bystanders — especially children — well clear of your work area. If the glass does crack during drilling, stop immediately and assess whether it's safe to continue or whether the pane needs replacing.
When to Call a Professional
There are situations where drilling glass yourself isn't the right call:
- You're unsure whether the glass is tempered or laminated
- The glass is in a safety-glazing location (shower screens, doors, low-level windows) — incorrect handling could breach the NZ Building Code
- You need a large hole (over 50 mm) or multiple holes close together
- The glass is expensive, antique, or irreplaceable
- You need a perfectly clean, polished edge for a professional finish
A qualified glazier has the tools, experience, and knowledge to drill glass cleanly and safely — and can advise you on whether your glass type is even suitable. You can find a trusted local glazier on tradedirectory.co.nz.
Window & Glass Association
