Burr. A roughness or projection of metal formed by a cutting or shaping tool created during blanking, piercing, trimming, turning, engraving or inscribing. Burrs form at different places during the stages of coin and medal manufacture – it is always necessary to remove them. In blanking or triming a burr occurs on the side of the piece where the blanking or trimming die exists (as if the tool leaves a trail of metal debris), this is called the burr side. In production blanking burrs are removed by deburring, as a separate step, or part of upsetting. In coining a burr can form where excess metal squeezes out between the die and the collar especially the thin ridge (fin or wire edge) formed at the rim/edge juncture on a piece struck in a coining press. In open die striking at the center of the outer edge (forming the flash). In casting at the junction of the molds (the parting line). In engraving each bite creates a burr. In edge turning a large medal the burrs fall away as the edge is made smooth (see turning off). On medals, minor burrs are usually removed by the finishing process (as with abrasive blasting); if the burrs are severe they must be chased by hand. See deburr, unusual shape.
excerpted with permission from
An Encyclopedia of Coin and Medal Technology
For Artists, Makers, Collectors and Curators
COMPILED AND WRITTEN BY D. WAYNE JOHNSON
Roger W. Burdette, Editor