| 摘要 |
A reaming type rock boring drill having an innermost cutter, rotatably supported as a beam. A sleeve or other support member disposed close to, but spaced apart from, the drill stem that forms a portion of the bit body serves as a trunnion or journal for the inner end of the load pin of the cutter bearing assembly. Drilling with such an assembly results in an uncontacted kerf of rock contiguous with the pilot hole. This kerf is disintegrated by mounting the innermost cutter so that the forces applied to the borehole bottom by this cutter act along a line directed into the formation and inwardly toward the pilot hole. As a result, a much higher cutting efficiency is achieved, when contrasted with earlier dispositions in which the innermost cutter acted directly on the bottom of the bore hole immediately adjacent the pilot hole. |
