Mechanism for rotating a spool adapted to receive a supply of filament, about the axis of the spool, comprising an electric motor which moves bodily axially toward and away from the spool to make and break the spool drive, respectively. According to the invention, the motor is mounted for limited rotation relative to its support, against the action of a spring, when the tension in the filament increases, thereby to make gradual the rise in tension of the filament. A limit switch is provided to limit this bodily rotation of the motor; and upon actuation of the limit switch, the motor is withdrawn from the spindle, thereby interrupting the spindle drive and releasing the torque that was applied by the filament to the motor, whereupon the motor is rotated by the spring back to a rest position.