Percussion drill bit having centrally projecting insert

Claim 1

A drill bit of the type to be mounted in a drill rod through which percussion forces are to be exerted for percussion drilling, said drill bit comprising: a bit body defining a longitudinal axis and including a front face extending generally transversely relative to said axis, and a longitudinal mounting portion coaxial with said axis and having a conical surface for connection to a drill rod of corresponding conical shape by means of substantially longitudinal frictional forces; a plurality of button inserts formed of cemented carbide, said inserts comprising: a central insert extending forwardly outwardly of said front face in alignment with said longitudinal axis, and one annular circumferential row of outer inserts formed by all remaining ones of said inserts, said outer inserts being equidistantly spaced radially from said central insert, said outer inserts being arranged in pairs, the inserts of each said pair being diametrically opposed on opposite sides of said central insert and inclined at an acute angle relative to said longitudinal axis and define the outer diameter of the hole drilled by the drill bit, the outer end of said central insert extending longitudinally forwardly beyond the forward ends of said outer inserts to define a pilot insert.