| 摘要 |
A rotary drilling tool has a plurality of cutters mounted on the tool body and formed with cutting edges defining a cutting profile. The cutters include at least two concentric arrays of primary preform polycrystalline diamond cutters which are radially spaced so as to define an annular groove in the cutting profile, between the two arrays. The deepest part of the groove in the cutting profile is defined by secondary preform polycrystalline diamond cutters located at a radial position which is intermediate the radial positions of the two arrays of primary cutters, so that in use the secondary cutters remove the tops of annular ridges of formation left between the arrays of primary cutters.
|
