A pendant motor is a flexible-shaft rotary tool in which the motor itself is mounted overhead, on a stand or wall bracket, and connected to the working handpiece by a flexible cable. The handpiece accepts a wide range of burs, separating discs, mandrels, and polishing wheels, and the motor delivers torque through the cable as the operator manipulates the handpiece freely with one or both hands. The geometry — heavy motor up high, light handpiece down at the work — is the reason the form has dominated bench-jewellery and stone-setting workshops for the better part of a century.

Form and major brands

The dominant bench-jewellery brand is Foredom, a Connecticut manufacturer whose Series SR and Series CC motors are the workshop standard across North America and much of the international trade. Foredom's foot rheostat, hanging motor, and quick-change handpiece together comprise the reference configuration. The Japanese manufacturer NSK produces a competing line, with the EMAX Evolution and Volvere systems aimed at higher-precision applications including watchmaking and dental laboratory work, where speeds above thirty thousand revolutions per minute and very low runout are required. European brands including Faro and Marathon round out the market.

Bench jewellers typically stock a pendant motor for general work and a separate micromotor — a small, high-speed handpiece with the motor in the handpiece itself — for the finest stone setting. The micromotor lacks the torque of a pendant motor but has lower vibration and finer balance for tasks where the operator's hand control is the limiting factor.

What it is used for

The pendant motor is the bench's general-purpose rotary tool. Stone setters use it with cup burs, hart burs, and seat burs to cut bezels, prong seats, and pavé pockets. Finishers use it with split mandrels, abrasive rubber wheels, and felt buffs to clean up casting flash, deburr edges, and bring up early polish. Polishers use it with bristle and chamois wheels charged with rouge for final lustre work, and lapidary technicians use it with diamond burs and small cup wheels for cabochon shaping and surface repair.

In the workshop

Pendant motors are referenced in IGS technical guides, in Lapidary Journal, and in the bench-jeweller texts including Alan Revere and Charles Lewton-Brain. A working setup includes the motor hung from a bench-mounted swing arm or wall bracket, the cable supported clear of the bench top so it does not catch on stones or work, the foot rheostat positioned for comfort, and a small caddy of frequently used burs and wheels within reach of the dominant hand. Maintenance is straightforward: cable lubrication every few hundred hours, brush inspection on brushed-motor models, and replacement of the cable when its inner shaft begins to rotate noticeably faster than the handpiece chuck.

Further reading

• International Gem Society — bench tools and equipment
• GIA Gems & Gemology — bench-practice articles
• International Gem Society — lapidary equipment