Abstract: The hammermill includes a housing, a working chamber defined by a polygonal screen, an inlet to the chamber, an outlet and a plurality of free-swinging hammers attached to a driven rotor. Support brackets extend the length of the housing and mount deflectors for eliminating tangential motion of materials being comminuted in the working chamber in the region of the deflectors. Side doors mount screen carriages for movement toward and away from the doors. In a closed position of the door, springs bias the screen carriages into engagement with wear-linings and the support brackets. The doors are pivotal away from the housing for access to the screens and the interior of the working chamber. A bottom screen carriage is movable toward and away from the chamber for access to the bottom screen sections.