Cutting insert and indexable rotary cutting tool

A rotary cutting tool having a rotational axis (O) and a tool rotational direction (K) around the rotational axis (O), the rotary cutting tool comprising:

• a disk shaped tool body including two substantially circular side end surfaces and an outer peripheral portion provided between the side end surfaces, a median plane (21M) perpendicular to the rotational axis (O), located between the two circular side end surfaces and bisecting the tool body,
• the tool body having a plurality of insert mounting seats arranged alternately in a staggered manner on both side end surfaces, along an outer peripheral edge portion of the tool body in the circumferential direction around the rotational axis (O), each insert mounting seat having a seating surface, and
• a cutting insert detachably mounted on each of the insert mounting seats, the cutting insert having a mounting hole provided with a mounting hole axis (A) around which the insert has 180° rotational symmetry, the cutting insert comprising:
• a first end surface;
• a second end surface being opposite to the first end surface;
• and a peripheral side surface extending between the first end surface and the second end surface,
• wherein at least one cutting edge having an arc shape is formed on an intersecting ridgeline portion between the peripheral side surface and at least one of the first end surface and the second end surface, and
• wherein the cutting edge is formed so as to follow one first curved shape having a constant first curvature radius when the cutting insert is viewed from the end surface thereof, and is formed so that at least over half the cutting edge follows one second curved shape having a constant second curvature radius when the cutting insert is viewed from the side surface thereof, and
• wherein the seating surface of the insert mounting seat is formed in a sloped manner such that, in a direction parallel to the rotational axis (O), a distance from the median plane to the seating surface of the insert mounting seat gradually increases in the tool rotational direction (K).

A cutting insert comprising:

• opposing first and second end surfaces, each having a substantially parallelogram shape and four corner portions;
• a peripheral side surface extending between the first end surface and the second end surface, the peripheral side surface comprising a pair of opposing long side surfaces connecting to a pair of opposing short side surfaces;
• an insert median plane (1M) passing through the peripheral side surface, and between the first and second end surfaces, the cutting insert having mirror symmetry about the insert median plane;
• a mounting hole passing between the first and second end surfaces;
• an axis of rotation (A) passing through the mounting hole, the first and second end surfaces having 180° rotational symmetry about the axis of rotation (A);
• an intersecting ridgeline portion formed between the pair of long side surfaces and each of the first and second end surfaces;
• wherein:
• a cutting edge is formed on each intersecting ridgeline portion and extends the entire length from one short side surface to another;
• when viewed from its associated end surface, each cutting edge follows a first curved shape having a constant first curvature radius for its entire length;
• when viewed from its associated long side surface, said each cutting edge follows a second curved shape having a constant second curvature radius for more than one-half of its length but less than its entire length;
• and
• the first radius of curvature differs from the second radius of curvature.

A rotary cutting tool having a rotational axis (O) and a tool rotational direction (K) around the rotational axis (O), the rotary cutting tool comprising:

• a disk shaped tool body including two substantially circular side end surfaces and an outer peripheral portion provided between the side end surfaces, a median plane (21M) perpendicular to the rotational axis (O), located between the two circular side end surfaces and bisecting the tool body,
• the tool body having a plurality of insert mounting seats arranged alternately in a staggered manner on both side end surfaces, along an outer peripheral edge portion of the tool body in the circumferential direction around the rotational axis (O), each insert mounting seat having a seating surface, and
• a cutting insert detachably mounted on each of the insert mounting seats, the cutting insert having a mounting hole provided with a mounting hole axis (A) around which the insert has 180° rotational symmetry, the cutting insert comprising:
• a first end surface;
• a second end surface being opposite to the first end surface;
• and
• a peripheral side surface extending between the first end surface and the second end surface,
• wherein at least one cutting edge having an arc shape is formed on an intersecting ridgeline portion between the peripheral side surface and at least one of the first end surface and the second end surface, and
• wherein the cutting edge is formed so as to follow one first curved shape having a constant first curvature radius when the cutting insert is viewed from the end surface thereof, and is formed so that at least over half the cutting edge follows one second curved shape having a constant second curvature radius when the cutting insert is viewed from the side surface thereof, and
• wherein the cutting inserts are mounted on each side of the median plane (21M) such that, in a direction parallel to the rotational axis (O), a distance from the median plane to an operative cutting edge of each cutting insert gradually increases as the cutting edge approaches the rotational axis (O).