The Challenge of Drilling Stone

You have spent the afternoon combing the beach and found the perfect, perfectly smooth pebble. Or perhaps you just spent hours cutting a lovely agate teardrop cabochon. Now, you want to turn it into a pendant, which means it needs a hole for a leather cord or a silver bail.

Drilling stone requires an entirely different approach than drilling wood, plastic, or metal. Wood is drilled by slicing away material with sharp steel edges. Stone is drilled by grinding away material using friction.

If you try to force a drill through a rock the way you would through a 2x4, you will destroy your bit, shatter the stone, and potentially injure yourself. Here is the master guide to drilling stone safely.

1. The Right Tools: Diamond Core Bits

Put your standard steel drill bits away. They are useless here. You must use diamond-coated drill bits.

There are two main types of diamond bits used in lapidary:

  1. Solid Diamond Burrs: Good for carving and widening existing holes, but terrible for drilling straight through a stone, as the solid flat tip has nowhere for the rock dust to escape.
  2. Diamond Core Drills: These are tiny, hollow cylinders coated in diamond grit. As they drill, they remove a tiny "core" of stone, creating much less friction and allowing water to flow inside to cool the bit. This is what you should use.

2. The Submerged Method (Water is Mandatory)

Heat and friction kill diamond bits instantly. You absolutely cannot drill stone dry. Not only will the bit burn up in seconds, but the localized heat expansion will cause your stone to crack (thermal shock).

Furthermore, drilling dry produces silica dust, which is incredibly dangerous to inhale.

The Setup

  1. Find a shallow plastic dish or Tupperware container.
  2. Place a small piece of scrap wood or stiff rubber at the bottom.
  3. Place your stone on top of the wood.
  4. Fill the dish with water until the stone is submerged by roughly a quarter-inch.

3. The 45-Degree Start

One of the most frustrating things for beginners is trying to start the hole. A diamond core bit is hollow and has no "center point" to anchor it. If you try to drill straight down (at a 90-degree angle), the bit will violently skate across the surface of the wet stone, scratching it horribly.

The Solution:

  1. Turn your Dremel, Foredom, or drill press on to a medium-high speed.
  2. Bring the drill bit down at a 45-degree angle.
  3. Gently touch the edge of the spinning bit to the stone until it grinds a small, crescent-shaped notch.
  4. Once the notch is established (which acts as a guide), slowly stand the drill up to a 90-degree vertical position.

4. Pumping and Flushing

Do not apply heavy downward pressure. Let the weight of the tool and the diamond grit do the cutting. If you press hard, the stone will crack.

As you drill, you must pump the bit up and down continuously (e.g., drill for 2 seconds, lift the bit out for 1 second, repeat). This "pumping" action allows the water to rush into the hole, flushing out the heavy rock mud and cooling the tip of the bit. If you don't pump, the mud will pack into the hole, causing the bit to overheat and burn out.

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Safety Warning: You are operating an electric tool near a pool of water. Ensure your rotary tool is plugged into a GFCI (Ground-Fault Circuit Interrupter) outlet, and make sure your hands and the body of the tool remain dry.

5. Preventing Blowout (The Flip Method)

You are 95% of the way through the stone. You get excited, press a little harder, and suddenly—POP. A massive, jagged chunk blows out the back of your stone, ruining the pendant.

This is called "blowout." As the drill breaches the back wall of the stone, there is no longer any material supporting the pressure, and the stone shears off.

How to avoid blowout:

  1. Drill exactly halfway through the stone.
  2. Stop, take the stone out, and flip it over.
  3. Carefully align your drill on the exact opposite side (you can mark it with a sharpie beforehand or hold it up to a strong light to see the shadow of the hole).
  4. Drill from the back until the two holes meet perfectly in the middle.

This method ensures a clean, perfectly chamfered hole on both sides of the stone, ready for your wire-wrapping or silver bail!