| 摘要 |
A rotary drill bit comprises a bit body (10) having a shank (11) for connection to a drill string (12) and a passage (13) for supplying drilling fluid to the face of the bit, which carries a plurality of polycrystalline diamond preform cutting elements (15). In order to reduce bit whirl, the cutting elements are so disposed as to apply a resultant lateral imbalance force (16) to the bit as it rotates during drilling and the gauge of the bit body is provided with low friction bearing pads (20) to transmit said resultant lateral force to the sides of the borehole. Each low friction bearing pad includes an outwardly facing cavity which is connected to the passage (13) by a choked conduit (21) so that, in use, drilling fluid under pressure is delivered to the cavity, which thereby acts as a low friction hydrostatic bearing surface. <IMAGE> |
