A flex shaft (also called a flexible shaft machine) is a motorised rotary tool system in which a ceiling- or bench-mounted motor transmits rotational power to a handheld working head through a long, torsionally flexible cable enclosed in a protective sheath. Unlike a rigid power tool, the motor never enters the craftsperson's hand; only the slim handpiece does, allowing it to be held and manoeuvred with the precision of a writing instrument. The result is a tool capable of driving grinding burs, diamond-coated points, polishing wheels, drill bits, and engraving cutters with fine control across stone, metal, and shell. In lapidary studios and jewellery workshops worldwide, the flex shaft has been a standard fixture since the mid-twentieth century, and the American brand Foredom remains so closely identified with the category that the two names are often used interchangeably in the trade.

Mechanical Principles

The motor unit — typically rated between one-sixth and one-third horsepower — is suspended from a ceiling hook or a dedicated stand so that its weight is entirely removed from the operator's hand. A braided or wound steel inner cable rotates inside a flexible outer casing, transmitting torque along a path that can curve and flex as the operator moves. Variable-speed foot pedals or electronic controllers allow the shaft to be run anywhere from a few hundred revolutions per minute up to approximately 30,000 rpm, giving the craftsperson the ability to match speed precisely to the task: slow for controlled stone drilling, fast for metal polishing or aggressive grinding. The handpiece accepts interchangeable collets — most commonly in 3.17 mm (one-eighth inch) and 2.35 mm sizes — that grip a wide variety of rotary accessories.

Applications in Lapidary and Stone Work

In lapidary practice, the flex shaft excels at operations that demand localised, controlled material removal rather than the broad surface work performed by a flat lap or a cabbing wheel. Typical applications include:

• Drilling through rough or finished stones using sintered or electroplated diamond core drills, with water or a water-soluble coolant introduced at the drill point.
• Carving and sculpting soft to medium-hard materials — coral, turquoise, malachite, amber, jet — with ball-end or flame-shaped diamond burs.
• Undercutting and channel-cleaning in stone-set jewellery, where a diamond bur removes material from a seat to achieve precise bearing contact with a gemstone's girdle.
• Pre-polishing and final polishing of carved or engraved surfaces using felt, rubber, or muslin wheels charged with diamond paste or oxide polishing compounds.
• Inlay work, where cavities are routed into a host material to accept contrasting stone or shell.

The tool is equally at home in the metalsmith's bench, where it drives gravers for stone setting, abrasive points for wax and metal finishing, and wire brushes for surface texturing — functions that place it at the intersection of lapidary and jewellery-making disciplines.

Historical Context

Before motorised flexible shaft tools became widely available in the mid-twentieth century, many of the same operations were accomplished with hand-held bow drills, push drills, or small bench-mounted drill presses that offered far less manoeuvrability. The adoption of the flex shaft — and particularly the proliferation of affordable, reliable machines from manufacturers such as Foredom Electric Company (founded in Bethel, Connecticut) — effectively industrialised fine detail work in small studios, reducing the time and physical effort required for drilling, carving, and setting without sacrificing the hand-guided precision that distinguishes craft from mass production. John Sinkankas, in his foundational lapidary technical literature, documented the flex shaft as an essential studio instrument, a status it has retained without serious challenge.

Selecting and Using a Flex Shaft

For most lapidary and jewellery applications, a motor in the one-quarter to one-third horsepower range with electronic variable-speed control offers the most versatility. Key practical considerations include:

• Handpiece type: Quick-change handpieces that accept collets without a separate wrench are preferred for production work; standard screw-collet handpieces are adequate for occasional use.
• Shaft length: A longer shaft — typically around 100 cm — gives the operator freedom of movement without the motor intruding into the work area.
• Coolant management: When drilling or grinding stone, water cooling is essential both to extend tool life and to suppress silica-bearing dust, which poses a respiratory hazard. A small recirculating water bath or a drip feed directed at the bur point is standard practice.
• Speed matching: Diamond burs in stone generally perform best at moderate speeds with light pressure; excessive speed without adequate coolant causes rapid bur wear and thermal fracturing of the stone.

Further Reading

• International Gem Society — Lapidary Tools Overview