Throw-away tipped drill, throw-away tip, and drill main body

A throw-away tipped drill, in which: a pair of chip disposal grooves are formed on the outer peripheral surface of a drill main body which rotates around an axial line, At an end portion of said drill main body, a concave groove shaped tip attachment seat is formed which, along with connecting to said pair of chip disposal grooves, also opens at an end surface of said drill main body. To said tip attachment seat, a throw-away tip of approximately a flat plate shape, upon an edge of which a pair of cutting edges are formed, is fitted by the pair of internal side surfaces of said tip attachment seat being mutually brought towards one another by a clamp bolt which is screwed into an end portion of said drill main body so that it crosses said tip attachment seat. Along with a pair of outer side surfaces of said throw-away tip respectively confronting a pair of internal side surfaces of said tip attachment seat, a pair of raked surfaces, which are portions of said pair of outer side surfaces of said throw-away tip which face towards the forward rotational direction of the drill, respectively, open into said pair of chip disposal grooves. By forming concave portions on the internal side surfaces of said tip attachment seat which do not contact against the outer side surfaces of said throw-away tip, pressure portions are created and are positioned more to the rearward direction of the rotational direction of the drill than the central axial line of said clamp bolt. When said clamp bolt is tightened up, said pressure portions press against the outer side surfaces of said throw-away tipped drill.