How to Drill Holes in Resin Without Cracking It

Resin drills cleanly when it’s fully cured and you go slow. It cracks when you rush, use the wrong bit, or skip the lubrication. The crack usually happens at the entry point — a small spider fracture that ruins a piece you’ve otherwise finished perfectly.

The good news: there’s a reliable technique that works almost every time, and the equipment is inexpensive.

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Wait for full cure

This is the step people skip. Soft or partially cured resin doesn’t drill — it tears. The bit grabs the material instead of cutting it, generates heat faster, and flexes the piece, which is exactly what causes cracking.

Most casting epoxies reach demolding hardness in 18–24 hours but full cure in 48–72 hours. Drill after full cure. If you’re not sure, press your fingernail into a flat area — if it leaves a mark, wait longer.

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The right tools

Pin vise: A small hand-held chuck that spins a bit by hand. For 1–2 mm holes in resin jewelry, this is the safest option. You have complete control over speed and pressure. A good pin vise costs $10–15 and lasts forever.

Rotary tool (Dremel or similar): Works well at low speed (5,000–10,000 RPM). High speed generates heat faster than the resin can dissipate, which softens the material around the hole and causes microfractures. If you’re using a rotary tool, go low and slow.

Drill press: For larger work, a small benchtop drill press gives perfectly perpendicular holes and consistent depth. Overkill for small jewelry but ideal for production work.

Bits: Use a standard twist drill bit in HSS (high-speed steel). For resin specifically, a fresh sharp bit is more important than bit type — a dull bit drags instead of cuts and causes far more heat and tearing. Sizes:
– 1 mm: fine for ear wires and small jump rings
– 1.5 mm: most common for pendant jump rings
– 2 mm: larger jump rings, bails

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Lubrication

Dry drilling generates heat. Heat softens resin, which causes the bit to grab and the piece to crack.

A drop of water at the drill site is enough. Some people use a bit of beeswax on the bit. Either works — the point is keeping the bit and the resin cool and letting the chips clear out of the flute. Stop every few seconds, lift the bit, let heat dissipate, add another drop of water if needed.

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The actual technique

1. Mark your hole location with a pencil or marker dot. For pendants, check the hang point first — hold the piece from the intended drill spot to see if it hangs level before you commit.

2. Place the piece on a firm surface — a scrap of wood works, or hold it in a clamp. Don’t hold resin jewelry pieces freehand while drilling; if the bit catches, it can crack or spin the piece into your fingers.

3. Start with very light pressure. Let the bit find its bite before applying any downward pressure. A wandering bit that skids across the surface scratches the piece.

4. Drill slowly. For a pin vise, steady manual rotation. For a rotary tool, low speed (5,000 RPM or below). Keep the bit perpendicular to the surface.

5. Add a drop of water. Drill a few turns. Lift. Repeat. For a 2 mm hole through 6 mm of resin, this takes maybe 30–60 seconds total. Not a fast process.

6. When you break through the back, ease off pressure completely — breakthrough cracking happens when you’re pushing hard and suddenly there’s no resistance.

7. Remove burrs around the hole with a toothpick or a larger bit run backward by hand.

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When it cracks anyway

Usually one of three things: the piece wasn’t fully cured, the drill speed was too high, or the hole is too close to the edge.

Keep holes at least 3–4 mm from any edge. Thin edges have no material to absorb the bit’s force, so they crack. If you have a cracked piece that’s otherwise intact, a drop of UV resin into the crack and 60 seconds under a lamp will bond it back — not invisible, but workable.

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Alternatives to drilling

Not every piece needs a drilled hole. Options:

Embedded bail: Pour a tube bail into the resin during cure. No drilling required. Covered in the findings guide.

Glue-on bail: Adhered to the back with two-part epoxy after curing. Works for pendants that will have predictable, light-to-moderate wear.

Wire wrapping: Wrap fine-gauge wire (24–26 gauge) around the cured piece to create a frame with an attached loop. Decorative and no drilling required. Common in boho and artisan jewelry styles.

Drilling is the most versatile option, but it’s not always necessary. For most of my standard pendant shapes, I drill — I like the clean look of a jump ring through a hole versus a glue-on bail. But for small detailed pieces where drilling near the edge is risky, glue-on bails are the call.

Browse bmmold.com molds for pendants and earrings.

What size hole do you need, and for what kind of piece? That changes the tool recommendation a bit.

— Nikolai