Importance

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Abstract

An earth-boring bit has a bit body and at least one cutter rotatably secured to the bit body. The cutter has a cutter shell surface including a gage surface intersecting a heel surface. A plurality of hard metal inserts are arranged in generally circumferential rows on the cutter and include a heel row of heel inserts on the heel surface of the cutter and a gage row of gage inserts on the gage surface of the cutter. At least one scraper insert, formed of material more wear-resistant than that of the cutter shell surface, is secured to the cutter shell surface generally at the intersection of the gage and heel surfaces. The scraper insert includes a gage and a heel insert surface. The gage and heel surfaces of the scraper insert converge to define a cutting edge for engagement with the sidewall of the borehole, the heel insert surface defining a positive rake angle with respect to the sidewall of the borehole of between 0 and 15 degrees. The cutting edge projects from the heel surface an amount not greater than the lesser of one-half the projection of the heel inserts from the heel surface and 30% of the pitch between the heel inserts.

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First Claim