A cabbing machine — also called a cab machine or cabochon machine — is a multi-wheel lapidary arbor designed to carry a stone through the complete sequence of operations required to produce a finished cabochon: rough shaping, fine grinding, sanding, and final polish. It is the central piece of equipment in any workshop oriented towards cabochon cutting, and its design has remained fundamentally stable for decades while individual components have been refined considerably.

Construction and layout

The machine consists of a horizontal steel shaft, or arbor, driven by an electric motor and carrying a series of wheels mounted side by side. A typical unit accommodates four to eight wheels, each dedicated to a specific stage of the cutting sequence. Water is delivered continuously to each wheel — either by drip feed or by a splash tray — to cool the stone, flush away swarf, and prolong wheel life. The entire assembly is usually enclosed in a splash hood with individual water ports above each wheel position.

Wheel diameters most commonly run at six or eight inches (approximately 150–200 mm), though compact hobby machines may use smaller diameters. Motor ratings range from a fraction of a horsepower on entry-level units to one horsepower or more on professional models; variable-speed motors allow the operator to reduce surface speed when working delicate or heat-sensitive material.

Wheel sequence

The wheel set progresses from aggressive material removal to fine finishing. A typical sequence is as follows:

• Coarse grinding wheel — usually a metal-bonded or resin-bonded diamond wheel, commonly 80 or 100 grit, used to rough-shape the preform and establish the dome profile.
• Fine grinding wheel — diamond-bonded, typically 220 or 260 grit, refining the shape and removing scratches left by the coarse stage.
• Sanding wheels — one or more wheels at 600, 1200, or 3000 grit, often constructed of rubber, cork, or resin-impregnated cloth, further smoothing the surface.
• Polishing wheel — felt, leather, or a specialised composite pad charged with a polishing compound such as cerium oxide, aluminium oxide, or tin oxide, depending on the material being worked.

Some operators insert an additional pre-polish stage — a worn or very-fine sanding wheel — between the last sanding step and the polishing wheel, particularly when working hard or optically demanding stones such as chrysoberyl or sapphire.

Operation

Before cutting, the rough stone is attached to a short wooden or aluminium rod called a dop stick using dopping wax or a two-part epoxy adhesive. The dop provides a handle that keeps the operator's fingers clear of the rotating wheel while allowing precise control of the stone's angle and orientation. The lapidary presses the dopped stone against the face of each wheel in turn, rotating and tilting it continuously to develop an even, symmetrical dome. Skill lies in maintaining consistent pressure and angle, reading the surface under reflected light, and recognising when each stage is complete before advancing to the next.

Manufacturers and market

Three American manufacturers have dominated the English-language market for several decades. Covington Engineering (Redlands, California) produces a range of machines from compact units to heavy-duty professional models and is particularly noted for robust construction. Lortone (Mukilteo, Washington) is widely used in educational and club settings for its accessible price point. Diamond Pacific Tool Corporation (Barstow, California) manufactures the well-regarded Genie series, which introduced a tilting splash hood and individual water controls for each wheel position and has become a benchmark for mid-to-professional-grade cabbing. Comparable machines are produced by manufacturers in Germany, Japan, and China for their respective regional markets.

Materials suited to cabbing

The cabbing machine is appropriate for virtually any opaque, translucent, or phenomenal gemstone material that displays its optical character best as a smooth dome rather than a faceted form. Common subjects include chalcedony, agate, jasper, turquoise, malachite, labradorite, moonstone, star sapphire, star ruby, cat's-eye chrysoberyl, opal, and nephrite jade. Transparent materials are occasionally cabbed — particularly when asterism, chatoyancy, or colour zoning makes a flat table desirable — but faceting machines are generally preferred for transparent rough intended to display brilliance.

Maintenance

Diamond wheels require periodic cleaning with a dressing stick to unclog the bond matrix and restore cutting action. Polishing wheels must be kept free of contamination from coarser grit stages, as a single misplaced abrasive particle can introduce deep scratches at the polishing step that are difficult to remove. Water quality matters: hard water deposits can accumulate on wheel surfaces and in the splash tray, and many lapidaries use filtered or softened water to reduce maintenance frequency.