Importance

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Abstract

A rotary cone drill bit (10) with two-stage cutting action is provided. The drill bit (10) includes at least two truncated conical cutter assemblies (20) rotatably coupled to support arms (18), where each cutter assembly (20) is rotatable about a respective axis (44) directed downwardly and inwardly. The truncated conical cutter assemblies (20) are frusto-conical or conical frustums in shape, with a back face (60) connected to a flat truncated face (22, 62) by conical sides. The truncated face (22, 62) may or may not be parallel with the back face (60) of the cutter assembly (20). A plurality of primary cutting elements or inserts (24) are arranged in a predetermined pattern on the flat truncated face (22, 62) of the truncated conical cutter assemblies (20). The teeth (26) of the cutter assemblies (20) are not meshed or engaged with one another and the plurality of cutting elements (24) of each cutter assembly (20) are spaced from cutting elements (24) of other cutter assemblies (20). The primary cutting elements (24) cut around a conical core rock formation (40) in the center of the borehole, which acts to stabilize the cutter assemblies (20) and urges them outward to cut a full-gage borehole. A plurality of secondary cutting elements or inserts (52) are mounted in the downward surfaces of a dome area (50) of the bit body (12). The secondary cutting elements (52) cut down the free-standing core rock formation (42) when the drill bit (10) advances.

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First Claim