An electroplated diamond bit is a rotary cutting tool in which a single layer of diamond abrasive particles is bonded to a metal substrate — typically steel — by means of an electrodeposited nickel matrix. Because the diamond grains are held in a thin metallic film rather than embedded throughout a sintered body, they protrude aggressively from the working surface, delivering fast, efficient material removal in hard substances including gemstones, glass, and ceramics. The trade-off for that cutting speed is a finite working life: once the single layer of diamond is consumed or dislodged, the bit is spent and cannot be redressed.

Construction and bonding method

In manufacture, a steel blank of the desired profile is first cleaned and prepared, then coated in a slurry containing diamond grit of a specified particle size. The assembly is submerged in a nickel-sulphamate or nickel-sulphate electrolytic bath; an applied electrical current causes nickel ions to plate out over the substrate, encapsulating the base of each diamond crystal and locking it in place. The resulting bond layer is typically 30–50 per cent of the diamond grit diameter in depth, leaving the upper portion of each crystal fully exposed and free to cut. Grit sizes used in lapidary applications commonly range from approximately 60 mesh (coarse, for rapid stock removal) to 600 mesh (fine, for delicate or thin-walled work).

Profiles and configurations

Electroplated bits are manufactured in a wide variety of profiles to suit different drilling tasks:

• Core drill (tube drill): A hollow cylinder that cuts an annular kerf, leaving a core of material intact. The standard choice for drilling through-holes in beads and cabochons.
• Ball-end and sphere bits: Used to initiate curved recesses or to enlarge and shape existing holes.
• Cylinder (straight-wall) bits: Suited to flat-bottomed blind holes and channel work.
• Cone and taper bits: Employed for countersinking or for enlarging holes progressively.

Shank diameters follow standard collet sizes (most commonly 2.35 mm for pendant drills and flexible-shaft machines, or 3.175 mm for larger rotary tools), making electroplated bits broadly compatible with equipment already found in most lapidary workshops.

Use in lapidary work

In gemstone drilling — whether producing the axial holes of drilled beads, the suspension holes of pendants, or the setting recesses of inlay work — electroplated bits are the most widely used category of diamond tooling, valued for their low unit cost and immediate cutting aggression. They perform well in quartz-family materials, feldspar, calcite, malachite, turquoise, and softer organic gem materials such as coral and shell. For harder, tougher species such as corundum (hardness 9 on the Mohs scale) or jadeite, electroplated bits remain serviceable but wear more rapidly; sintered or metal-bond bits may prove more economical for sustained production drilling in such materials.

Continuous water cooling is not merely advisable but essential. Water serves three simultaneous functions: it dissipates frictional heat that would otherwise carbonise the diamond surfaces and anneal the nickel bond; it flushes swarf from the cutting zone, preventing clogging; and it reduces micro-fracturing of the workpiece caused by thermal shock. A simple water bath — with the workpiece submerged to a depth that keeps the bit tip flooded — is the standard workshop arrangement. Intermittent pecking (lifting the bit periodically to allow fresh coolant to flood the hole) is recommended for deep drilling.

Comparison with sintered and metal-bond bits

Sintered diamond bits distribute diamond particles throughout the full depth of the bond matrix; as the outer surface wears, fresh diamond is continuously exposed, giving a self-sharpening characteristic and a substantially longer service life. Metal-bond (brazed) bits offer similarly extended longevity. Electroplated bits sacrifice longevity for a lower purchase price and a more aggressive initial cut. For small-scale or intermittent lapidary use — drilling occasional beads or cabochons — the economics favour electroplated tooling. For production environments or for drilling very hard gem materials in quantity, the higher initial outlay for sintered bits is generally recovered through reduced replacement frequency.

Care and practical notes

Because the bond layer is thin, electroplated bits are vulnerable to lateral loading: side pressure, wobble from an unbalanced spindle, or forcing the bit into a workpiece at an angle can strip the diamond layer prematurely. A drill press or purpose-built lapidary drilling jig is strongly preferable to freehand operation. Running speeds for gemstone drilling typically fall in the range of 1,000–3,000 rpm depending on bit diameter; larger-diameter bits require lower speeds to maintain an appropriate surface velocity at the cutting edge without generating excessive heat.