A double-cone bur — also known as a bicone bur — is a rotary cutting tool used in jewellery setting to mill a precise V-shaped seat, or bearing, into a metal mount. Its defining characteristic is a pair of conical cutting surfaces that meet at a central ridge, producing a symmetrical bicone profile. When rotated at speed in a pendant drill or flex-shaft handpiece, this profile cuts a clean, angled groove into which a stone's girdle or pavilion edge can rest securely. The double-cone bur is a standard instrument in the professional setter's toolkit, valued for the geometric control it affords when preparing prong, bezel, and channel settings.

Form and Function

The tool's two opposing cones share a common axis and meet at their widest point — the central ridge — which acts as the cutting apex. As the bur is pressed into metal, the upper cone opens the entry of the seat while the lower cone defines the undercut angle. The resulting V-groove conforms closely to the profile of a faceted stone's girdle, distributing bearing pressure evenly around the circumference rather than concentrating it at a single point. This even distribution reduces the risk of chipping brittle stones and prevents the rocking or tilting that can occur when a seat is cut too shallowly or at an imprecise angle.

Double-cone burs are manufactured in a range of diameters — typically from under one millimetre to several millimetres — to correspond with the full spectrum of stone sizes encountered in production and bespoke jewellery work. The cone angle itself varies by manufacturer and intended application; steeper angles suit stones with a more acute pavilion, while shallower angles accommodate flatter profiles. Burs intended for precious-metal work are commonly made from high-speed steel (HSS), while those designed for harder alloys such as platinum or white gold are often carbide-tipped for extended cutting life.

Use in Setting Practice

In prong setting, the double-cone bur is used to cut a notch into each prong at the height at which the stone is to sit. The setter selects a bur whose diameter matches or very slightly exceeds the stone's girdle thickness, then cuts each prong to the same depth, ensuring that the stone seats level and at a consistent height around its circumference. Consistency across all prongs is critical: an uneven bearing causes the stone to tilt, stresses individual prongs unevenly, and can compromise long-term security.

In bezel and channel settings, the bur may be used to refine the interior ledge or to open a bearing groove along the inner wall of the setting. Here the bicone geometry helps the setter establish the correct angle relative to the stone's pavilion slope, so that when the bezel or channel wall is pushed over, it contacts the stone at the girdle rather than bearing down on the crown or table.

Proper technique requires that the bur be run at an appropriate speed — generally moderate, with light, controlled pressure — to avoid overheating the metal or the tool itself, either of which can dull the cutting edges prematurely. Lubrication with a small amount of cutting wax or bur lubricant extends tool life and produces a cleaner seat surface.

Relationship to Other Setting Burs

The double-cone bur belongs to a broader family of setting burs that includes the ball bur, the hart (or hart-shaped) bur, the bearing bur, and the cup bur, each suited to a different stage of the setting process or a different seat geometry. Where the ball bur is used to open a round recess and the hart bur to cut a bearing for a flat-bottomed stone, the double-cone bur is specifically chosen when a V-profile seat is required — most commonly for round brilliant, oval, and other faceted stones whose girdles benefit from a symmetrical angular cradle. In many workshops the double-cone bur is used in combination with other burs: a ball bur to rough out the initial recess, followed by the double-cone to refine the bearing angle to the precise geometry required.

In the Trade

Double-cone burs are supplied by specialist jewellery tool manufacturers and distributors worldwide and are considered consumable items, replaced as their cutting edges wear. They are sold individually by diameter and, in professional supply catalogues, are often listed under the alternative designation bicone bur. Quality varies considerably between manufacturers; carbide versions command a higher price but offer meaningfully longer service life when working in hard alloys. For bench setters working at volume, maintaining a well-organised selection of double-cone burs in graduated sizes is as fundamental as any other aspect of tool management.