Abstract: A rotary drill bit (10) has fluid discharge nozzles (36A, 36B, 36C) positioned between adjacent pairs of roller cutters (20A, 20B, 20C). A fluid discharge nozzle (36A) provides a stream of drilling fluid (44) directed toward an adjacent roller cutter (20A) and slanted toward the bore hole side wall away from a radial direction at a slant impact angle B for first impacting the side wall (34), and then sweeping in a high velocity stream along the corner surface (33) and inwardly across the bore hole bottom (32) at cutting element engagement locations (39).

Abstract: A rotary drill bit (10) has fluid discharge nozzles (36A, 36B, 36C) positioned between adjacent pairs of roller cutters (20A, 20B, 20C). A fluid discharge nozzle (36A) provides a stream of drilling fluid (44) toward an adjacent roller cutter (20A) inclined radially outwardly toward the side wall (34) of the bore hole (30) and slanted toward the roller cutter (20A) for first striking the side wall (34), and then sweeping inwardly across the bore hole bottom (32) in a flat high velocity stream tangential to bit rotation and beneath the cutting elements (26) during cutting engagement of the gage row (28D) with the formation.

Abstract: A rotary drill bit (10) has three roller cutters (20A, 20B and 29C) mounted thereon for rotation with a plurality of cutting elements (26) arranged in concentric annular rows (28A, 28B, 28C, 28D) thereon. A high velocity drilling fluid is discharged from nozzle orifices (40, 42, 52) and the orifices are sized and positioned so that more hydraulic energy is directed against the cutting elements (26) in the gage row (28D) than against the cutting elements (26) in the remaining rows (28A, 28B, 28C). The drilling fluid impinges the cutting elements (26) on the leading side of the roller cutters (20A, 20B, 20C) immediately prior to engagement of the cutting elements (26) with the bore hole bottom (30) and then sequentially strikes the bore hole bottom formation at or closely adjacent the juncture (35) of the horizontal bottom portion (32) with the vertical side portion (34).

Abstract: A rotary drill bit (10) having a plurality of roller cutters (20) with rows (32A, 32B, 32C, 32D) of cutting inserts (34,36,38,40) mounted within sockets (35,46) on the frusto-conical cutter body (30). The cutting inserts 34,36,38,40) have cutting surfaces formed with a wear-resistant material with certain cutting inserts (36,38) being formed of a wear-resistant material having a hardness higher than the hardness of the wear-resistant material on the remaining inserts (34,40) in each row. The hard cutting inserts (36,38) are positioned in each row in a predetermined pattern intermingled in a generally uniformly spaced pattern with the softer cutting inserts (34,40) and comprising generally between 20% and 50% of the total number of cutting inserts in a particular row.