there is disclosed a hard rock trench cutting machine comprising a main body assembly and a cutting wheel assembly . a cylinder is transversely mounted on the main body assembly and carries a pair of pistons which extend axially from each end of the cylinder . pads are provided on each piston to bear against the sidewalls of a trench . each piston has an end face within the cylinder which , together with an inner sidewall of the cylinder , comprises a pressure chamber adapted to force the pads against the trench . the main body and its cylinder are free to move laterally relative to the pistons when the cylinder is pressurized . extensible arms are provided between the pistons and the main body assembly for forcing the main body assembly and its cutting wheel forwardly to progressively cut a trench . a steering assembly is provided to shift the main body assembly laterally relative to the pistons and about the central axis of the cutting wheel .