Rock drill bit with stress relief insert sockets

Claim 1

A rock drill bit comprising: a steel body including a front peripheral surface, said surface having a plurality of holes extending longitudinally inwardly from said surface, said holes each including: a steel cylindrical wall portion, a steel bottom wall portion defining the longitudinally inner end of said hole, a radially enlarged steel transition wall portion extending between a longitudinally inner end of said cylindrical wall portion and a radially outward end of said bottom wall portion, a plurality of hard metal inserts mounted in said holes and projecting outwardly of said surface, said inserts each including a side surface comprising: a cylindrical surface portion directly abutting against said cylindrical wall portion of said hole, said cylindrical surface portion extending longitudinally inwardly at least as far as said longitudinally inner end of said cylindrical wall portion of said hole and terminating short of said bottom wall portion, a tapered surface portion extending longitudinally and radially inwardly from said longitudinally inner end of said cylindrical surface portion, and a radially disposed bottom surface portion defining a longitudinally inner end of said insert said bottom surface portion abutting against said bottom wall portion, said transition wall portion of said hole extending from said longitudinally inner end of said cylindrical wall portion in a longitudinally inward and radially outward direction and later extending longitudinally inwardly and radially inwardly and finally adjoining said bottom wall portion, and having a configuration whose concave portions are smoothly curved to eliminate abrupt concave corners liable to cause localized stress concentrations in the wall of the hole and subsequent fatigue failure therein.