| 摘要 |
In a rolling cutter drill bit the distribution of the inserts on each rolling cutter is arranged to form a more rounded borehole corner to reduce concentrated side forces and to facilitate directional drilling while minimising gauge wear. Each rolling cutter includes a transition row of inserts which is intermediate the gauge cutting row and bottom cutting row and which drill neither the gauge of the borehole nor the hole bottom, but drill a rounded transition area between the vertical side wall and borehole bottom. The invention provides the ratios between certain key dimensions of the insert rows, such ratios being selected to determine the roundness of the corner of the borehole in such manner as to improve the ability of the bit to drill curved boreholes. These key dimensions include the relative diameters and spacing of the insert rows, the relative diameters of the inserts, and their relative angular orientations with respect to the longitudinal axis of the drill bit.
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