Abstract: A milling device for performing a milling operation comprising a milling unit comprising a housing defining a milling chamber that can be filled with a material to be milled, a rotor assembly rotatably mounted in the housing, and a screen assembly for fractionating the material milled by the rotor assembly in movement and extending below the rotor assembly; and a drive unit adapted for controlling the movements of the rotor assembly relative to the screen assembly during the milling operation; wherein said drive unit is configured to produce an oscillating movement of the rotor assembly, the oscillating movement having an oscillation angle that can be varied during the milling operation when controlling the movements of the rotor assembly relative to the screen assembly. The milling device has improved milling efficiency.