Rock Bit and Inserts With a Chisel Crest Having a Broadened Region

An insert for a drill bit comprising:

• a base portion;
• a cutting portion extending from the base portion, wherein the cutting portion includes a pair of flanking surfaces that taper towards one another to form an elongate chisel crest having a peaked ridge;
• wherein the elongate chisel crest extends between a first crest end and a second crest end, and has an apex positioned between the first and second crest ends, the apex defining an extension height for the insert;
• wherein the elongate chisel crest has a transverse radius of curvature that increases moving from the first crest end toward the apex, and increases moving from the second crest end towards the apex.

A drill bit for cutting a borehole having a borehole sidewall, corner and bottom, the drill bit comprising:

• a bit body including a bit axis;
• a rolling cone cutter mounted on the bit body and adapted for rotation about a cone axis;
• at least one insert having a base portion secured in the rolling cone cutter and having a cutting portion extending therefrom;
• wherein the cutting portion includes a pair of flanking surfaces tapering towards one another to form an elongate chisel crest having a peaked ridge;
• wherein the elongate chisel crest extends between a first crest end and a second crest end, and has an apex positioned between the first and second crest ends, the apex defining an extension height of the at least one insert;
• wherein a transverse cross-section at the apex has an apex transverse radius of curvature, a transverse cross-section at the first crest end has a first crest end transverse radius of curvature that is less than the apex transverse radius of curvature, and a transverse cross-section taken at the second crest end has a second crest end transverse radius of curvature that is less than the apex transverse radius of curvature;
• wherein the apex transverse radius of curvature is at least 10% larger than the first crest end transverse radius of curvature, and at least 10% larger than the second crest end transverse radius of curvature.

A drill bit for cutting a borehole having a borehole sidewall, corner and bottom, the drill bit comprising:

• a bit body including a bit axis;
• a rolling cone cutter mounted on the bit body and adapted for rotation about a cone axis;
• at least one insert having a base portion secured in the rolling cone cutter and having a cutting portion extending therefrom;
• wherein the cutting portion includes a pair of flanking surfaces tapering towards one another to form an elongate chisel crest having a peaked ridge;
• wherein the elongate chisel crest extends between a first crest end and a second crest end, and has an apex positioned between the first and second crest ends, the apex defining an extension height of the at least one insert;
• wherein the elongate chisel crest has a transverse width at a uniform depth D measured perpendicularly from the peaked ridge, wherein the transverse width of the elongate crest increases moving from the first crest end toward the apex, and increases moving from the second crest end towards the apex, the ratio of the depth D to the extension height being 0.10.