Checked 22 September 2026
Gem drilling machines and diamond drill bits
A gem drill makes a hole in a stone held steady and kept wet. The drill tip sets the hole size; the other end must fit the machine's grip, called a chuck. Check both sizes before buying a bit.
Control the feed and hold the stone
A bench gem drill guides the bit along a set path. A carving handpiece offers freer movement for recesses and details, but the operator must keep it aligned by hand. For a through-hole in a bead or pendant, check how the stone is held and how the drill advances before comparing motor ratings.
Covington's current 605 Manual Gem Drill uses a lever with a ¾-inch stroke, a foot-controlled variable-speed motor and a water pan. Its listed ¼-inch Jacobs chuck describes the maximum shank it can grip; it does not mean the finished hole is ¼ inch. The maker describes it as a light-duty machine for medium to soft gem material or glass.
Record the cut, shank and depth separately
For a solid diamond drill, record cutting diameter, usable length and shank size. For a hollow core drill, add the inside diameter of the core it leaves. Confirm that the chuck or collet accepts the shank and that the bit maker permits the machine's speed and feed. A photograph of a tiny cutting tip does not show the mounting dimensions.
The diamond-drill section compares solid, Triple Ripple and core-drill dimensions. Covington lists bits and a bead vise alongside its drills. Crystalite's current drill table, printed page 17, gives only cutting sizes for its solid drills, so check their shanks separately; for core drills it lists outside, inside and shank diameters.
Keep the bit and stone cool
Covington's 605 instructions keep the work submerged and use a press-and-release motion so coolant reaches the cut. They also say to secure the drill to a level bench. Follow the instructions for the exact machine and bit, including guards, speed and electrical protection. Do not dry-drill stone or press hard enough to stall or overheat the bit.
Use a bead vise or another fixture that holds the piece without putting fingers in the bit path. The work must stay stable as the bit enters and exits. A container and backing block must withstand the bit if it passes through; Covington's instructions put a small piece of wood under the stone so the bit cannot pierce the dish.
Identify an old drill by its controls
Covington's two rotary gem drills are the 605, which it still sells, and the 600 Automatic Gem Drill, which it no longer lists. The 605 has a hand lever. The 600 has no lever: its motor raises and lowers the chuck ¼ inch by itself. Covington's 2023 listing for the 600 gives a 1/50-horsepower motor turning at 3,000 rpm and a ¼-inch Jacobs chuck, and says the light automatic feed spares diamond bits but drills slowly.
Covington still hosts the 600 instructions. They cover diamond bits and the cheaper alternative: drill tubes fed with boron-carbide grit. Check the motor plate, feed mechanism, chuck, pan and included vise before ordering bits or repairs.