An apparatus (10) comprising a pair of associated chopper drums (20), including a top chopper drum (21) and a lower chopper drum (22). The chopper drum (20) defines an axial cylindrical bore (25) having a rotational axis (26) into which is mounted a drive shaft (not shown) that is keyed radially to drive the chopper drum (20). Radially spaced from the rotational axis (26) are a plurality of outwardly facing recesses (30) defined by walls of a body of the chopper drum (20). Each recess (30) extends longitudinally along the periphery of the chopper drum end-end to provide a recess for mounting a corresponding plurality of cutting blades (35). Each recess is defined by a longitudinally extending lower wall (31) and an opposed and circumferentially spaced. The cross sectional profile of the chopper drum (20) is generally consistent throughout its length and includes a plurality of ridges (26) and troughs (27) with the ridges (26) built up to define therein the recesses 30, the ridges (24) being interposed by the troughs (27). A higher side wall (32) provides support for the cutting blade (35) and is inclined relative to a plane (36) extending radially outwardly from the rotational axis (26). The opposed smaller side wall (31) supports a wedge clamp (40).
