A self-propelled boring type mining machine includes a mobile frame and a pair of spaced apart drive shafts that extend forwardly from a gear box mounted on the frame. A pair of rotary boring heads are nonrotatably connected to the pair of drive shafts and are operable to cut a pair of bores in a mine face to dislodge the mine material. Cusps formed at the mine roof and floor are dislodged by upper and lower cutter chains that are carried by upper and lower cutter bars movably positioned on the front end of the frame. Cutter bar extensions are movably positioned on both sides of the upper and lower cutter bars by control links pivotally connected to the extensions and the mobile frame. The upper and lower cutter bars are vertically extended and retracted by piston cylinder assemblies. Movement of the cutter bars is transmitted to the cutter bar extensions which are guided on the respective cutter bars along combined horizontal and vertical paths. Thus the cutter bar extensions are automatically moved to an operating position corresponding to a preselected position of the cutter bars for supporting the cutter chains in a preselected cutting position on the mobile frame.