Patent ID: 7281594

Claim:
A rock drill bit adapted for percussive drilling, the drill bit comprising: a bit body and a head portion defining a longitudinal center axis, the head portion including an axially forward rock-crushing surface and a skirt extending axially rearwardly from the rock-crushing surface, said rock-crushing surface comprising several rock-crushing means, a circumferential outer surface of the skirt being formed with circumferentially spaced apart grooves forming lands therebetween, the grooves and the lands extending generally in an axial direction, an axially rearward portion of a land is provided with a guiding surface, said guiding surface facing radially outwardly, said drill bit having a waist at its mid portion, wherein the guiding surface comprises at least one step or a sloping surface such to reduce the diametrical dimension stepwise or continuously, respectively, wherein the guiding surface comprises a first guiding portion and a second guiding portion both situated radially outside of an imaginary extension line of the waist, wherein the first guiding portion projects farther radially outwardly than the second guiding portion relative to the center axis of the drill bit, and wherein each guiding portion is of part-cylindrical shape and wherein the first guiding portions are defined by a first diameter and wherein the second guiding portions are defined by a second diameter.