Shaping with Mandrel
Shaping with Mandrel
Bench technique for forming and sizing rings, bangles, and circular work
Shaping with a mandrel is a foundational bench technique in jewellery fabrication, in which a tapered or cylindrical steel rod (the mandrel) provides a rigid form over which sheet, wire, or part-finished work is hammered, pressed, or rolled to achieve a specified circular or oval geometry. The mandrel is the simplest and most universal forming tool in the bench repertoire and underpins ring sizing, bangle forming, and a wide range of related operations.
The ring mandrel
The ring mandrel is a long tapered steel rod, typically 30 to 38 cm in length, with a circular cross-section that tapers continuously from the heavy end to a slim tip. The taper rate is engineered so that incremental diameter changes correspond to standard ring sizes. The mandrel is engraved with size markings — US sizes 1 through 16, UK sizes A through Z plus halves, or the equivalent in continental and Asian sizing systems — and a ring placed on the mandrel reads its size against the markings.
Working operations on the ring mandrel include sizing up by hammering the band against the larger taper, sizing down by compression after a section is cut out, and rounding a soldered band by mallet planishing. The mandrel is held in a vice or supported by a bench-mounted ring mandrel holder, leaving both hands free for the hammer or mallet and for repositioning the work.
The bracelet mandrel
The bracelet mandrel is larger, typically oval rather than purely round, and sized to the dimensions of standard bangles and cuffs. The oval geometry reflects the cross-section of the human wrist; round bracelets are formed on round mandrels for the lower-arm circumference, while oval mandrels are used for fitted bangles. Forming on a bracelet mandrel produces the bangle's overall shape; final adjustment for fit is then done by hand or against a wooden flexing block.
Other mandrel forms
Specialist mandrels exist for square and oval rings, for chenier (tubing) work, for chain links, for bezel cups, and for hollow forming in spinning and silversmithing. The principle is consistent: a mandrel of known geometry imposes that geometry on the metal worked over it. Steel is the standard material for most mandrels because of its hardness, dimensional stability under hammering, and resistance to deformation; wooden and plastic mandrels are used where the metal is delicate or already finished and steel contact would mar the surface.
Working considerations
Hammering on a mandrel work-hardens the metal — desirable for the durability of finished work, but also a constraint, since work-hardened metal is more difficult to size further and more prone to cracking on subsequent forming. Annealing between forming passes is standard practice for substantial size changes. Soldered seams should be properly fluxed and at full strength before mandrel work begins, since hammering across a weak seam will open it.
In the trade
The ring mandrel is the bench's most-used sizing tool and is one of the first instruments any apprentice learns to operate. Bench technicians size dozens of rings a day on the mandrel, and the technique is the basis on which the resizing and repair side of every retail jewellery business operates. The mandrel is also the form on which custom and commission rings are first roughed out, before the head and details are added.