Rock drill bit

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, and
• 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
• a radially disposed bottom surface portion defining a longitudinally inner end of said insert,
• said transition wall portion of said hole extending from said longitudinally inner end of said cylindrical wall portion of said hole in a direction having at least a radially outward component, then extending in a direction having longitudinally inward and radially outward components, thereafter extending in a direction having longitudinally inward and radially inward components and finally adjoining said bottom wall portion, so as to contain no abrupt concave corners which cause localized stress concentrations in the wall of the hole and subsequent fatique failure therein;
• the ratio of:
• the radial distance from the cylindrical surface of said insert to the radially outermost part of said transition wall, to
• the diameter of said cylindrical surface of said insert,
• being in the range of from 1:25 to 1:75.