A device for cutting trenches in hard rock. A plurality of disc-like primary cutters are positioned on arms around a frame. The frame rotates about a central shaft and the center shaft is moved along horizontally in the direction the trench is to be cut. Between the primary cutters are reaming cutters. Each primary and each reaming cutter is provided with a plurality of spaced apart indentors secured to the external surface and each indentor has an end point and being adaptable to penetrate the rock face upon the application of working force a distance "P" and wherein the indentor end points are spaced a distance not greater then 7P apart.
