Abstract: A machine to comminute refuse includes a drum-like rotor on a rotor axle inside a housing. The rotor includes two face-to-face outwardly diverging part-conical discs each supporting a plurality of shear plates which have spaced-apart teeth along outer edges thereof. The teeth of each shear plate lie in a plane which includes the axis of said rotor and extends radially outwardly therefrom. An anvil in said housing also has spaced-apart teeth positioned to be in intermeshing relation to the shear plate teeth as the shear plates rotate with the rotor. Rubbish to be comminuted is fed into the machine at position directly above the axle of the rotor and is carried by the shear plates and shear teeth into contact with the anvil and anvil teeth, shearing off the portions of the refuse aligned with the shear plate teeth and carrying this refuse through to position under the rotor where it is discharged vertically from the machine.