n. In mech., a cylindrical bar or spindle, either of uniform diameter, of different diameters, or tapered, used for a variety of purposes, but chiefly for the support of objects formed with holes, into which the mandrel is forcibly driven in order to hold them firmly while turning in a lathe, or in an analogous machine, or in operating upon them with a file.n. A miners' pick.n. In metal-working by the spinning process, the form, usually of wood, upon which the thin plate of metal or blank is pressed in order that the revolution may give it the form of the mandrel.n. A mandrel fitted to a bearing or bearings of a support which may be set in the tool-post of the slide-rest of a lathe, or in some other traversing device. Such mandrels are used for expanding reamers and analogous tools, and they are usually driven by a pulley-and-belt mechanism.To operate upon with mandrels, as a bronze gun.