A rocker mill includes a rollstand and a carriage for supporting and repositioning a workpiece extending through the rollstand. A first hollow-shafted electric motor is mounted on the carriage and includes a first hollow open-ended rotor and threaded nut through which the stationary feedscrew passes. The threaded nut is connected to the first motor to be rotated thereby in order to move the carriage longitudinally toward the rollstand. A second hollow-shafted electric motor is mounted on the carriage and includes a second hollow open-ended rotor and a clamp through which the workpiece passes. The clamp is actuated into clamping engagement with the workpiece for transmitting rotational and longitudinal movements thereto. Such mechanism for imparting rotary and longitudinal movements to the workpiece is of very low inertia and thus is able to reposition the workpiece with a high degree of precision.