Rolling cone bit with shear cutting gage

In a rolling cutter of an earth-boring bit having a gage surface for contacting a sidewall of a borehole as the cutter rotates about its axis and rolls over the bottom of the borehole, the gage surface having a plurality of gage inserts, each gage insert secured by interference fit into a socket formed in the gage surface, an improved gage insert comprising:

• at least one of said gage inserts having an elongated cylindrical body partially inserted in a selected socket in the gage surface, the body formed of a hard, fracture-tough material;
• the gage insert having a cutting end extending a selected distance from the gage surface, the cutting end formed of a super-hard, abrasion-resistant material;
• the cutting end of said insert having a substantially flat abrasion-resistant face substantially normal to a longitudinal axis of the body of the insert;
• a generally conical circumferential cutting surface connecting the face and the body of the gage insert at a selected angle to define an arcuate cutting edge to shear the sidewall of the borehole;
• and
• the selected angle of the cutting surface defining a negative rake angle with respect to a portion of the sidewall of the borehole being sheared.

In a rolling cutter of an earth-boring bit having a gage surface for contacting a sidewall of a borehole as the cutter rotates about its axis and rolls over the bottom of the borehole, the gage surface having a plurality of gage inserts, each gage insert secured by interference fit in a socket formed in the gage surface, an improved gage insert comprising:

• at least one of said gage inserts having an elongated cylindrical body partially inserted into a selected socket in the gage surface, the body formed of a hard, fracture-tough material;
• the gage insert having a cutting end extending a selected distance from the gage surface, the cutting end formed of a super-hard, abrasion-resistant material;
• the cutting end of said insert having a substantially flat abrasion-resistant face substantially normal to a longitudinal axis of the body of the insert;
• a generally conical partially circumferential cutting surface connecting the face and the body of the gage insert at a selected angle to define an arcuate cutting edge to shear the sidewall of the borehole;
• a substantially planar cutting surface connecting the face, the body, and the generally conical first cutting surface of the gage insert at a selected angle to define a substantially linear cutting edge to shear the sidewall of the borehole;
• and
• the selected angle of each cutting surface defining a negative rake angle with respect to a portion of the sidewall of the borehole being sheared.