A self-propelled boring type mining machine includes a mobile frame and a pair of spaced apart rotor drive shafts extending forwardly from the mobile frame. Rotary cutter arms are nonrotatably connected to the rotor drive shafts for cutting a pair of overlapping bores in a mine face to dislodge solid material. Cusps formed at the mine roof and floor are dislodged by upper and lower cutter drum assemblies pivotally mounted transversely on the frame front end portion. The lower cutter drum assembly includes an intermediate drum section separated by gaps from a pair of end drum sections. Gear cases extend into the gaps to rotatably support a transverse drive shaft that is drivingly connected to the intermediate and end drum sections. The centerlines of the gear cases are spaced inboard of the centerlines of the rotor drive shafts. The end drum sections are helically splined to the drive shaft so that upon rotation of the drive shaft, the end drum sections rotate and advance longitudinally on the drive shaft between a retracted position and an extended position to control the width of cut in the mine face. By positioning the gear cases inboard of the rotor drive shafts when the end drum sections are extended the area left uncut between the cutting paths of the rotary cutter arms and end drum sections is minimized.