Cutter unit assemblies for excavating machines and to excavating machines including cutter unit assemblies

An excavating machine for excavating rock from a working face to extend an underground roadway or tunnel, comprising a stay unit anchorable in the roadway or tunnel and having a slideway which when the stay unit is installed in the roadway or tunnel extends longitudinally along the roadway or tunnel, and a cutting unit assembly slidably supported on said stay unit comprising a body and a boom adapted to carry a rotary cutter for excavating rock from the working face, the body comprising a non-rotary portion presenting annular support means which are arranged generally coaxially with the longitudinal axis of the roadway or tunnel, and a rotary portion provided with a pivotal mounting for pivotally supporting the boom and having annular supported means for cooperation with the annular support means of the non-rotary portion of the body, one of the portions comprising a single gear ring assembly for drivable engagement by at least one driven gear wheel to rotate the rotary portion relative to the non-rotary portion, the annular support means, the annular supported means and the gear ring assembly substantially located adjacent to a radially outer margin of the body and in a common transversely extending plane, the non-rotary portion of the body further comprising a slide arrangement for slideable engagement with said slideway of the stay unit, the pivotally mounted boom having driven means for rotating the cutter, said cutting unit being slidable with respect to said stay unit whereby said cutting unit is advanced against a surface to be cut, cutting said surface to sump said cutting unit, means for urging said cutting unit away from said stay unit in opposition to cutting forces on said cutter only during the time said cutting unit is sumping into said surface, and means for fixing the position of said non-rotating portion with respect to said stay unit after said cutting head is sumped with respect to said surface.