A roller cone bit (11) has a ball retention system to secure the cones (17) to the head (15). A radial ball race (19) includes a ball way (21) with a ball plug (27) to keep the balls (25) in the ball race. The ball plug (27) is secured to the head by welding. Any residual stress in the weld region is alleviated by applying heat or vibration to promote relaxation.

A novel split threaded ring bearing member (42) for rolling cutter drill bits with at least a portion of its threads (48) having a different pitch than its mating threads (40) is disclosed. The pitch difference is designed so that the threaded ring can be seated or otherwise located precisely with respect to the other bearing elements within the drill bit to effectively control the axial displacement of the rolling cutter (18) on the bearing spindle (16) within a given tolerance range. Upon assembly, the difference in thread pitch causes the opposite, opposing mating thread flanks to engage, effectively applying a tensile or compressive force to a portion of the threaded ring bearing member (42), which gradually increases as the assembly is tightened. The result is an improved rolling cutter drill bit with a threaded ring cutter bearing system with excellent resistance to back-off which will not allow significant radial movement between the engaged threads, even if some back-off of the threads occurs.

Directional multi-blade boring heads (1000, 1050) are disclosed which have first and second blades (1030, 1032) which each define a deflecting surface (1036, 1038) for deflecting the boring head when the head is advanced without rotation. At least one intermediate blade (1034) extends between the deflecting surfaces in a three blade design. In a four blade design, a second intermediate blade (1042) extends on the side opposite the first intermediate blade (1034). The boring head is particularly effective in drilling a straight borehole through a variety of soil conditions when the boring head is simultaneously rotated and advanced along the direction of boring.

A method of manufacturing a rolling cutter drill bit comprising a bit body which carries cutter assemblies each of which includes a cutter journal (22) on the bit body, a cutter (18) rotatably mounted on the journal, and a threaded retention ring (30) screwed onto the cutter (18) to retain the cutter on the journal while permitting a limited degree of axial displacement of the cutter relative to the journal. The method comprises the steps of predetermining a desired magnitude of maximum permitted axial displacement between the cutter and the journal, and then employing components (30, 62, 68, 109) for the cutter assembly which are so dimensioned as to provide, when assembled to form the cutter assembly, a maximum permitted axial displacement (44) which is not greater than the predetermined magnitude. The appropriately dimensioned components may be specifically manufactured to the required size, or may be selected from a stock of components of differing sizes. Alternatively the maximum permitted axial displacement may be determined by adjusting the axial position of the retaining ring (30) on the cutter during assembly.

A method of manufacturing a rolling cutter drill bit of the kind where each cutter (18) is rotatably mounted on a bearing spindle (16) on the bit body (12) and is retained on the spindle by a threaded retention ring (42) in screw-threaded engagement with the cutter (18). The retention ring (42) is provided with an aperture (48) to expose a portion of the screwthread (40) on the cutter and an implement (52) is passed along a registering passage (26) in the spindle (16) and through the aperture (48) in the retaining ring (42) to deform or otherwise alter the exposed screwthread (40) in a manner to prevent subsequent relative rotation between the screw-threads, thereby locking the retention ring to the cutter. Instead of deforming the screw-thread (40) it may be formed with a recess (50) which is engaged by a pinning element (58) secured in the aperture in the retaining ring (42).

A rotary drill bit (10) having a roller cutter (28) retained on a journal (24) by an externally threaded retainer ring (52) mounted within an annular groove (48) in the journal (24). The radii (R1, R2) formed at the inner and outer corners of the groove (48) are designed by suitable formulas to provide adequate strength for the journal (24) including the flange (50) adjacent the groove (48).

A drill bit is shown which is connectable to the lower end of a rotary drill string for use in drilling oil and gas wells as drilling mud is circulated downward through the string, out the bit, and upwardly within the annulus between the string and well bore so as to remove cuttings therefrom. The bit has cones (31) which are mounted for rotation about thrust bearings which extend inwardly from the lower ends of legs which depend from a shank at the upper end of the bit body which is attached to the drill string. The cones are secured on the bearing journals by a system of sealed liquid passages (50-51) and reservoirs which provide a liquid lock requiring no retaining bearings or washers.