A diamond bit — also called a diamond drill — is a rotary cutting tool whose working surface is charged with industrial diamond particles, enabling it to bore through gemstone materials that would rapidly destroy conventional steel tooling. Because diamond is the hardest known natural substance (Mohs 10), bits incorporating it can penetrate quartz (Mohs 7), corundum (Mohs 9), beryl (Mohs 7.5–8), jade, and virtually every other lapidary material encountered in a gem workshop. Diamond bits are indispensable for bead drilling, pendant-hole work, earring fittings, channel and inlay preparation, and any application requiring a clean, dimensionally accurate hole in hard stone.

Construction and Types

Two principal manufacturing methods define the performance characteristics of diamond bits available to the lapidary trade.

• Electroplated bits. A single layer of diamond grit is bonded to a steel shank by an electrodeposited metal coating, typically nickel. Because the diamonds are exposed at maximum projection from the outset, electroplated bits cut aggressively and are well suited to short production runs or delicate work where precise control is required. Their limitation is longevity: once the single layer of abrasive wears away, the bit is spent and cannot be redressed.
• Sintered bits. Diamond particles are distributed throughout a powdered-metal matrix — commonly bronze, cobalt, or steel alloy — and the mixture is pressed and fired (sintered) to form a homogeneous cutting segment. As the outer diamond layer wears, fresh particles are continuously exposed from below, giving sintered bits a substantially longer service life. They are the preferred choice for production bead drilling and repetitive industrial work, though they typically require a brief break-in period to open the matrix and expose the initial cutting layer.

Geometry and Sizing

Diamond bits for gemstone work are manufactured in a wide range of diameters, from under 0.5 mm for fine bead drilling to 25 mm or more for core-drilling cabochon blanks or inlay recesses. The most common profiles are the core drill (a hollow tube that removes a cylindrical plug, reducing heat and material stress) and the solid twist drill (suited to smaller diameters where a hollow form is impractical). Twist-style bits benefit from fluted shanks that help evacuate slurry during drilling. Shank dimensions are standardised to fit Dremel-type rotary tools, flex-shaft handpieces, drill presses, and dedicated bead-drilling machines.

Technique and Coolant

Continuous water cooling is not optional — it is fundamental to successful diamond-bit drilling. Heat generated at the cutting interface can fracture thermally sensitive stones such as opal, tanzanite, or fluorite, and will rapidly destroy the bond matrix of any bit if allowed to build unchecked. In practice, the workpiece is submerged in a shallow water bath, or a small plasticine dam is built around the drill site and kept filled with water. Feed pressure should be light and rhythmic: excessive downward force glazes the cutting surface and accelerates wear without improving penetration rate. Periodic withdrawal of the bit — a technique sometimes called pecking — clears swarf and allows fresh coolant to reach the tip.

Applications in the Gem Workshop

The most common lapidary applications for diamond bits include:

• Drilling suspension holes in cabochons and tumbled stones for pendant or earring fittings.
• Producing stringing holes in gemstone beads, particularly in harder materials such as rock crystal, amethyst, carnelian, and nephrite jade.
• Creating recesses for flush or bezel inlay work in hardstone panels and decorative objects.
• Core-drilling rough material to extract oriented test cylinders for optical or spectroscopic examination.
• Enlarging or cleaning existing drill holes in antique beads where the original drilling tool left an irregular bore.

Selection and Care

Matching bit type to task is the primary selection criterion. Electroplated bits in fine grits (600–1200 mesh equivalent) are appropriate for finishing passes and fragile materials; coarser electroplated or sintered bits (100–400 mesh) suit rapid stock removal in robust stones. Bits should be stored dry and protected from contact with other metal tools, which can chip the exposed diamond layer. A sintered bit that appears to have stopped cutting can often be restored by briefly drilling into a soft abrasive block — such as a piece of aluminium oxide dressing stick — to re-expose fresh diamond from the matrix.