| 摘要 |
Method and apparatus for drilling a straight borehole in all types of geological formations by the provision of a drilling tool that maintains a constant hole angle respective to the vertical as the borehole is formed. The apparatus includes a bit to which there is rotatably secured a plurality of cones. The cones are mounted to a cutterhead, with the cutterhead being attached to the lower marginal end of a shank. The cutterhead is placed at an incline respective to the shank whereby a plane passing through the cones of the bit lies obliquely respective to the axial centerline of the shank. When the bit weight is applied, the oblique angle between the cones and the shank causes the drill string weight to be transferred unevenly to the cones, whereupon a significant radial force is effected on each of the individual cones. This resultant radial force is always directed in the same direction respective to an outside edge of the rotating bit, whereupon a specific part of the bit is forced towards the outside of the hole as the bit rotates through one revolution. A plurality of radially spaced rollers located immediately above the cutterhead stabilize the shank of the drilling tool.
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