Mandrel — The Tapered Steel Form Behind Every True Round
Mandrel — The Tapered Steel Form Behind Every True Round
The bench tool jewellers use to size, shape, and true rings, bracelets, and bangles
A mandrel is a tapered cylindrical tool, almost always of steel, used at the bench to shape, size, and measure rings and other circular jewellery. It is one of the oldest and most fundamental tools in goldsmithing — the form has changed little since the medieval period — and remains in daily use in every working jewellery shop. The principle is straightforward: a tapered steel form against which a metal circle can be hammered round, stretched larger, or measured against printed graduations.
Types in workshop use
The ring mandrel is the most familiar form, marked along its length with size graduations corresponding to the local sizing convention — letter sizes in the British system, numeric sizes in the American, and millimetre or French sizes elsewhere. A jeweller slides a finished ring down the mandrel until it meets resistance and reads the size at that point; the same tool serves to true an out-of-round shank by hammering it onto the steel form until it sits flush at the intended size. Ring mandrels are typically about 25 to 30 centimetres long, tapered from roughly 25 millimetres at the base to 10 millimetres at the tip.
Bracelet and bangle mandrels are larger-diameter variants of the same principle, used for shaping cuffs, hinged bangles, and rigid bracelets. They may be round, oval, or slightly flattened depending on the intended profile of the finished piece. Specialist mandrels also exist for forming knife-edge shanks, signet bezels, and other specific jewellery components.
How the mandrel is used
Sizing up a ring — increasing its diameter — is performed by placing the ring on the mandrel and striking the shank with a rawhide or nylon mallet, working around the circumference to stretch the metal evenly. The taper of the mandrel converts vertical force into radial expansion. Sizing down by stretching is not possible; reductions are made by cutting out a section, soldering, and re-trueing on the mandrel. The same tool is used to recover the round profile of a ring that has been damaged or worn out of shape.
Bench jewellers sometimes use a calibrated steel ring set rather than a mandrel for measuring finger size from a finished ring, but the mandrel remains the workshop standard for trueing and stretching operations. The tool is also indispensable in the early stages of fabrication, where a strip of metal is bent around the mandrel to form the initial circle before soldering.
Selection and care
A good mandrel is true round along its length, free of dents and burrs, and clearly marked with crisp graduations. Cheap stamped mandrels can be slightly oval or have indistinct markings, both of which compromise their utility. The working surface should be kept smooth; any dent or scratch will be transferred onto the inside of the ring being worked. We oil our mandrels lightly to prevent rust, and we keep separate mandrels for precious metal and base metal work to avoid contamination.
Mandrels are inexpensive — a quality steel ring mandrel costs less than fifty pounds — and a competent bench cannot operate without one. The tool is so universal that its presence in the workshop is taken for granted, but its absence stops production immediately.