A shearing apparatus for performing several modes of operation on travelling or stationary material. Two cooperative knife drums, which can be rendered rotatable or non-rotatable, form a gap whose spacing is varied by hydraulic piston cylinder assemblies, one mounted on opposed ends of the upper or bottom drum. The adjustable knife drum is held in a parallel or non-parallel positioning or caused to rock with or without additional high frequency oscillations by controlling and regulating the pressure in the cylinders, while simultaneously moving the upper drum towards the lower drum and/or rotating both drums.