| 摘要 |
An earth drilling bit that cuts concentric annular kerfs ahead of primary drilling means and thereby increases drilling rate. The bit includes a bit body having a lower end forming an annular cutter for cutting an outer annular kerf, an inner drill member positioned concentrically within the bit body having a lower end forming an annular cutter for cutting an inner annular kerf, a plurality of rotary drilling members attachedly arranged between the bit body and inner drill member positioned so lowermost cutting edges are above lowermost edges of the annular cutters of the bit body and inner drill member for removing material between the outer and inner annular kerfs, and plurality of drilling members attachedly arranged within the inner drill member positioned so lowermost cutting edges are above lowermost edges of the annular cutter of the inner drill member for removing material within the inner annular kerf. |
