| 摘要 |
The invention relates to a drill bit (10) having saddles (12) for a number of roller cutters (16-38) having two along the circumference of the roller cutter extending rows (41,42) of cutting means, said rows (41,42) being displaced internally in the axial direction of the roller cutter. A saddle (12) and adherent roller cutter (20) are so designed that the roller cutter is reversibly mountable in the saddle (12). The rows (41,42) of cutting means are locaed on each side of the transverse symmetry plane (45) of the roller cutter (16-32) . The distance (B) of the first row (42) is bigger than the distance (A) between the second row (41) and the symmetry plane (45) . The rows (41,42) of cutting means of a roller cutter (20) are arranged to move along a first series of circles (46,47) when the roller cutter (20) is mounted in a first position in its saddle (12) and along a second series of circles (48,49) when the roller cutter (20) is mounted in a reversed position in the saddle (12) in relation to said first position. |
