Patent ID: 8734069

Claim:
A rotary cutting tool comprising: a tool body having a shank portion and a neck portion protruding from the shank portion and formed externally in a circular truncated cone shape or a cylindrical shape; a recessed insert attachment seat formed at the tip of the neck portion of the tool body; and a circular plate-like cutting insert detachably mounted on the insert attachment seat so as to be coaxial with the axis line of the shank portion; wherein the insert attachment seat is provided with a bottom surface on which a side surface serving as a seating surface of the cutting insert is seated and a wall surface in contact with a peripheral surface of the cutting insert, a plurality of recessed grooves which are recessed from the bottom surface to extend in the circumferential direction of the neck portion and in a direction toward the shank, with both ends being opened to the outer peripheral surface of the neck portion from the wall surface, are formed on the bottom surface so as to travel around the insert attachment seat around the axis line, each of these recessed grooves extends in such a manner that at least the both ends thereof move radially to the outer peripheral side with respect to the axis line toward the both end sides from a circle which is centered on the axis line in contact with the center between these both ends, and the bottom surface extends between the mutually opposing ends of the recessed grooves adjacent in the circumferential direction.