Setting bur
Setting bur
Rotary cutter for preparing stone seats in metal
A setting bur is a small rotary cutting tool used at the jeweller's bench to prepare seats in metal that receive gemstones during setting. The bur is mounted in a flexible-shaft handpiece or a pendant drill and is rotated against the metal to cut a precisely shaped recess — typically conical, hemispherical, or cup-shaped — that supports the pavilion of the stone and locates it correctly relative to the surrounding setting structure. Setting burs are produced in graduated sizes corresponding to standard stone-girdle diameters and form one of the core consumable tools of bench setting alongside gravers, setting punches, and finishing burs.
Forms and profiles
The principal setting-bur profiles are the hart bur (round bur with cup-shaped tip, used for round-stone seats), the setting bur proper (a slightly tapered cup profile sized to match standard round-brilliant girdle diameters), the bearing cutter (with a flat tip and a cylindrical body, used for under-cutting bezels and creating bearing seats), the inverted-cone bur (used for cleanup and for cutting sharp internal angles), and various specialised forms for fancy-cut stones. Each profile produces a specific seat geometry: round burs produce hemispherical seats suited to round brilliants, while flat-tipped bearing cutters produce flat-bottomed seats with cylindrical sides.
Bur sizes are calibrated in tenths of a millimetre across the cutting head; common diameters run from approximately 0.5 mm for melée settings to over 5 mm for large-stone work. Setting burs are typically supplied as graded sets covering the principal diameter range; specialist bench workers maintain extensive bur drawers with hundreds of sizes and profiles to address the full range of work.
Materials
Setting burs are produced in high-speed steel, tungsten carbide, and (for finishing burs) diamond-coated steel. High-speed steel is the standard for most bench setting and offers a workable balance of cutting performance, cost, and tool life. Tungsten carbide burs offer materially longer life on hard alloys (platinum, hard gold solders) at higher cost. Diamond burs are used for cutting and shaping stones rather than for seat preparation, and operate by abrasion rather than the cutting-edge action of steel and carbide burs. Setting burs are consumables; even well-maintained burs require periodic replacement as the cutting edges dull or chip with use.
Technique
The bur is held in the handpiece and run at moderate speed (typically 5,000 to 15,000 rpm depending on the specific work) while being applied to the metal. Cutting fluid — usually a setter's lubricant or beeswax — is applied to extend bur life and produce a cleaner cut. The setter advances the bur slowly into the metal, watching seat depth and angle through magnification, and stops when the seat is correctly sized for the stone to seat at the right height. Common errors include cutting the seat too deep (which leaves the stone sitting low in the metal), too shallow (the stone sits high), off-axis (the stone tilts), or with chatter (the bur produces an uneven cut that compromises stone security).
In the trade
Setting burs are routine consumables for any bench operation engaged in stone setting. The standard suppliers — Otto Frei, Rio Grande, GRS, Stuller, and the European specialists — distribute burs across the full range of profiles and sizes. Quality varies materially: cheap burs from secondary suppliers cut acceptably for a small number of seats but dull rapidly, while premium burs from established makers maintain cutting edges across hundreds of seats. For production environments and high-end bench work, the economics favour the premium tools; for occasional use, lower-cost alternatives are workable.