Indexable rotary cutting tool and insert

An insert configured to be detachably mounted on a mounting seat provided at a tip end portion of a tool main body such that the tool body and the insert define an indexable rotary cutting tool, the mounting seat of the tool body comprising:

• a insert fit groove in a slit shape which is formed at the tip end portion of the tool main body to extend in a radial direction orthogonal to a rotation center axis including a tool rotation center axis;
• and a clamp screw configure to fix the insert inserted into the insert fit groove,
• the insert comprising a cutting edge portion,
• the cutting edge portion of the insert including:
• an outer peripheral cutting edge which extends along the rotation center axis direction;
• a rake face of the outer peripheral cutting edge;
• a bottom cutting edge which extends along the radial direction;
• a rake face of the bottom cutting edge;
• a cutting edge of a corner R which connects an outer end of the bottom cutting edge in
• the radial direction to a front end of the outer peripheral cutting edge in the rotation center axis direction and is formed in an arc shape to protrude toward an outer peripheral side of the tip end portion of the tool main body;
• a rake face of the cutting edge of the corner R;
• a chamfered surface which is formed in at least the rake face of the cutting edge of the corner R;
• a chip removal groove which is formed at a base end side of the rake face of the bottom cutting edge in the rotation center axis direction;
• and
• a chip removal groove which is formed at the inside of the rake face of the outer peripheral cutting edge in the radial direction, and
• wherein, within a virtual plane, which is perpendicular to a reference plane including a predetermined point on the cutting edge of the corner R and the rotation center axis;
• and includes a virtual straight line passing through an arc center point of the cutting edge of the corner R and the predetermined point, a true rake angle corresponding to an angle in which the rake face of the cutting edge of the corner R is inclined with respect to the reference plane is defined as a radial rake angle,
• an angle in which the virtual straight line projected to the reference plane is inclined with respect to the rotation center axis within the reference plane is defined as a radial angle,
• a point in which the virtual straight line inclined by the radial angle of 5° intersects the cutting edge of the corner R is defined as a reference point, and wherein
• a twist angle of the outer peripheral cutting edge has a positive value,
• an axial rake angle of the cutting edge of the corner R at a boundary point between the cutting edge of the corner R and the outer peripheral cutting edge has a positive value,
• the axial rake angle of the cutting edge of the corner R at the reference point has a negative value,
• the radial rake angle at least in a region between the boundary point and the reference point of the cutting edge of the corner R has a negative value, and
• the radial rake angle of the cutting edge of the corner R at the reference point is smaller than the radial rake angle of the cutting edge of the corner R at the boundary point.