Abstract: Much better control of the grind of a rotary mill and much more uniformity of grind of the mill is achieved by better control of air flow through the mill, provided by making the milled product collecting pan of the mill air-tight and regulating the amount of in allowed to escape from the pan. The apparatus of the invention includes a housing in which are mounted two discs in spaced, confronting axial alignment, each disc having extending therefrom toward the other disc concentric rows of teeth. The rows of teeth overlap so that alternating rows of radially spaced, interposed teeth are formed. One of the discs is adapted to be rotated in relation to the other disc and grain to be milled, along with any air flow through the mill, is introduced through an inlet to the area between the discs inwardly of the innermost rows of teeth. An outlet into a substantially air tight collecting pan is provided for the milled material after it passes radially outwardly through the interposed row of teeth.