A flame bur is a rotary cutting tool used in jewellery manufacture and stone setting, characterised by its elongated, tapering profile that narrows to a pointed tip — broadly resembling the shape of a candle flame. Mounted in a flexible-shaft handpiece or pendant drill, it allows the setter to carve, refine, and undercut metal seats with a degree of control that broader burs cannot achieve in confined spaces. Alongside the ball bur and the hart bur, the flame bur is one of the core cutting tools in a professional setter's kit.

Form and Construction

Flame burs are manufactured in a graduated range of sizes, typically expressed in tenths of a millimetre or in numbered increments, allowing the setter to match the tool closely to the diameter of the stone being set. The cutting head is formed with longitudinal flutes that remove metal as the bur rotates, while the tapered geometry concentrates cutting action at the tip and along the lower flanks of the tool. Most flame burs available in the trade are produced from high-speed steel (HSS) or tungsten carbide. Carbide versions hold a sharper edge for longer and are preferred when working in harder alloys such as white gold or platinum, where HSS burs dull relatively quickly. Both types are available with standard shafts sized to fit the collets of flexible-shaft machines and micromotor handpieces.

Function in Stone Setting

The primary application of the flame bur is the creation and refinement of the seat — the precise recess into which a gemstone's girdle and pavilion rest. After an initial hole is drilled or a pilot seat is opened with a ball bur, the flame bur is used to deepen and shape the seat to the correct angle and depth, ensuring the stone sits level, at the intended height above the metal surface, and without rocking.

The pointed tip is particularly valuable for forming undercuts: shallow lateral recesses cut beneath the girdle line of the stone that allow prong tips or bead raisings to be pushed over and grip the girdle securely. In pavé and bead setting, where multiple small stones are set in close proximity and the geometry of each seat directly determines whether the finished surface appears flat and even, the flame bur gives the setter fine positional control that a ball bur alone cannot provide. In prong setting, the tool is used to notch the inner face of each prong at the correct height so that the stone drops to a consistent level before the prongs are pushed over.

The tapered profile also allows the bur to reach into tight areas between existing settings or within channel walls without the shoulder of the tool contacting and damaging adjacent metalwork — an advantage that broader cutting tools do not share.

Use and Care

Flame burs are used at moderate rotational speeds; excessive speed generates heat that can anneal the cutting edges of HSS burs prematurely and risks burning lubricant residues into the metal surface. A light cutting oil or bur lubricant is commonly applied to extend tool life and improve the quality of the cut. Because the tip of the flame bur is the most delicate part of the tool, lateral pressure should be applied carefully: forcing the tip sideways rather than allowing it to cut on its flutes is the most common cause of tip breakage, particularly with carbide burs, which are harder but more brittle than HSS. Worn or chipped burs should be replaced rather than used on fine work, as an irregular cutting edge produces an uneven seat that compromises stone security.

In the Trade

Flame burs are stocked by all major jewellery tool suppliers and are considered consumable items in production workshops. They are sold individually and in assorted sets. The distinction between the flame bur and the closely related hart bur (which has a more pronounced V-shaped cross-section) is sometimes blurred in trade catalogues, but experienced setters treat them as complementary rather than interchangeable: the hart bur excels at cutting a clean, sharp-edged seat for a faceted girdle, while the flame bur's rounded taper is better suited to forming undercuts and refining curved seat walls.