GESTEINBOHRER

The tool comprises a drilling head (4) at the forward end. within which a forwardly extending cutting plate (6) is fitted or formed. First and second opposing axially extending channels are formed on the circumferential periphery of the drilling head. A clamping shank (2) is on the rearward end and fits within the tool holder of a rotary hammer. An intermediate helical conveying portion (10) extends between the drilling head and the clamping shank and comprises at least four helically extending flutes (14a-d) separated by corresponding helically extending webs (12a-d). The cutting plate is formed with a central chiseling dome and a pair of cutting edges extending radially outwardly from the chiseling dome. Each cutting edge has a trailing relief face and the acute angle (theta ) between the relief face and the longitudinal axis of the tool varies from the radially inner to the radially outer end of each cutting edge. The first axially extending channel extends axially rearwardly from a forward facing face of the drilling head into an number of the (at least) four flutes, and the second axially extending channel extends axially rearwardly from the forward facing face of the drilling head into a different number of the (at least) four flutes.