A roller is a machine used to turn metals into plates.

The rolling mill works by continuous circular action. Passing the body between the two cylinders, dragged by their rotation in the opposite direction, it is flattened and elongated, increasing its density. If the two cylinders are smooth, the metal is thus stretched into sheets. If they are grooved, cylinders are produced whose section corresponds to that of the grooves. If one of the cylinders has a relief and the other a corresponding hollow, the cylindrical body will reproduce the shape of the body generated by the interval of the two cylinders on the line of contact. The enormous resistance experienced by the rolling mill requires the use of a flywheel of considerable weight so that it can overcome the resistance that opposes the movement.

A small hardened steel cylinder called mullet and engraved in hollow or in relief allows, by a circular action analogous to that of the rolling mill, to engrave by mechanical action bodies less hard than it, namely copper, non-hardened steel, etc.

The rolling mill of smooth or grooved cylinders in the direction of the generatrices acting on non-malleable bodies produces destruction. Two types of wheels are also used:

Dictionary of agricultural arts and manufactures, C. Laboulaye, 1857.