How to Drill Glass and Gemstones Without Cracking Them

Diamond bits grind clean holes in glass and stone, but heat and pressure crack fragile pieces fast. Here is how to drill them safely.

Use the right bit

Diamond-coated bits grind hard, brittle material instead of cutting it. Match the size to your hole, and keep spares handy since the coating wears. Small 2mm and 3mm bits suit most jewelry work.

Always cool with water

Water is the single most important step. It cools the bit and washes away grit, preventing cracks and extending tool life. Drill in a shallow water bath or drip water on the spot as you go.

Start at an angle

Begin the hole tilted so the bit bites without skating. Once it grips, bring it upright. Starting flat lets the bit wander and scratch the surface before it cuts. A quality diamond bit set for glass and stone makes this easier with sharp, fresh tips.

Press lightly

Let the diamond do the work. Heavy pressure heats the piece and snaps it. Ease off near the far side, where material is thinnest and most likely to blow out.

Support the workpiece

Back the piece with a soft, firm surface and hold it steady. Movement chips the edges. A stable setup and a slow, patient pace give the cleanest holes.

The bottom line

Cool with water, start angled, press lightly, and support the piece. Patience beats speed when drilling glass and gemstones.