Abstract: A mill for producing finely divided particulate material copmrising a mill housing, a rotor adapted to rotate within the housing, an inlet for stock and an outlet for the finely divided particulate material, the rotor having at least one hammer, the hammer moves in direction of hammer travel and passes into close proximity with a miling surface to finely divide material at the milling surface during each rotation of the rotor, while during a major portion of the hammer travel the hammer is spaced away from any surface, the speed of the hammer through it's travel, position of the hammer, rotor, milling surface and relative dimensions of the hammer, rotor and milling surface being, such that during operation an air flow with the finely divided particulate material entrained therein is generated within the housing opposite the direction of hammer travel.