Rotary rock bit with multiple row coverage for very hard formations

Abstract

The body of the bit includes an axis of rotation, an upper end connectable with the drill string for rotating the bit and three downwardly projecting arms. Each of the arms includes an inwardly and downwardly inclined shaft defining an axis of cutter rotation with all of the axes intersecting at substantially a common point. First, second and third conical cutter members are journaled on a respective one of said shafts. Each cutter member includes a nose and a base with the base being oriented generally toward the wall of the well bore. A plurality of outwardly projecting, circumferentially-spaced inserts are located in annular rows in each cutter member for engaging the bottom of the well bore. At least two of the cutter members include intermediate rows of inserts disposed between the nose and base of the cutter member at approximately the same distance from the bit axis of rotation so that the inserts engage the bottom of the well bore at approximately the same distance from the bit body axis of rotation, thereby cutting overlapping tracks.