Abstract: A rock drill bit comprises a steel body including a front peripheral surface having a plurality of holes. Each hole includes a steel cylindrical wall portion, a steel bottom wall portion, and a radially enlarged steel transition wall portion extending between a longitudinally inner end of the cylindrical wall portion and a radially outward end of the bottom wall portion. A plurality of hard metal inserts are mounted in the holes. Each insert includes: a cylindrical surface portion directly abutting against the cylindrical wall portion of said hole and extending longitudinally inwardly at least as far as the longitudinally inner end of the cylindrical wall portion of the hole. The transition wall portion of the hole extends from the longitudinally inner end of said cylindrical wall portion of said hole so as to contain no abrupt concave corners which cause localized stress concentrations in the wall of the hole and subsequent fatigue failure therein.

Abstract: A rock drill bit is disclosed of the type comprising a steel body having a plurality of longitudinally extending holes, and a plurality of metal inserts mounted in the holes. Each hole includes a cylindrical steel wall portion, a bottom steel wall portion, and a radially enlarged transition steel wall portion extending between a longitudinally inner end of the cylindrical wall portion and a radially outward end of the bottom wall portion. Each insert includes a cylindrical insert portion directly abutting against the cylindrical wall portion of the hole. A cylindrical surface portion extends longitudinally inwardly at least as far as the longitudinally inner end of the cylindrical wall portion. The transition wall portion of the hole is smoothly curved continuously from the longitudinally inner end of the cylindrical wall portion to the bottom portion. The transition wall portion extends radially outwardly and longitudinally inwardly from the longitudinally inner end of the cylindrical wall portion.