Cutting insert and rotary cutting tool

A cutting insert having an approximately polygonal hexagonal shape, the cutting insert comprising:

• a first end face;
• a second end face;
• a side surface;
• a through hole formed on the first and second end faces defining a center axis and an axial direction;
• and
• a reference plane disposed perpendicular to the center axis and passing through the side surface;
• wherein the first end face sequentially comprises a main cutting edge and a corner cutting edge connected to the main cutting edge;
• a first cutting edge that includes the main cutting edge and the corner cutting edge, a second cutting edge, and a third cutting edge which are formed to be rotationally symmetric respectively with the first cutting edge, with respect to a center axis of the through hole as a reference;
• wherein the first end face is formed to be an approximately hexagonal shape and includes:
• a first corner in which the corner cutting edge is provided;
• two corners which are formed to be rotationally symmetric with the first corner by 120 degrees respectively, with respect to the center axis of the through hole as a reference;
• a second corner which adjoins the first corner has a larger vertical angle than the first corner, and includes the main cutting edge which is provided between the first corner and the second corner;
• and
• two corners which are formed to be rotationally symmetric with the second corner by 120 degrees respectively, with respect to the center axis of the through hole as a reference;
• wherein the side face includes a first side face portion connected to the main cutting edge, a second side face portion connected to the corner cutting edge, and a third side face portion connected in an axial direction to each of the first side face portion and the second side portion;
• the first side face portion has a negative clearance angle such that a distance from the center axis increases in the direction of approaching the reference plane, therefore having a reverse positive surface, and in a side view a height of the first side face portion increases gradually in a direction of approaching the corner cutting edge;
• the second side face portion has a negative clearance angle such that a distance from the center axis increases in the direction of approaching the reference plane, therefore having a reverse positive surface, and in a side view a height of the second side face portion is greater than a maximum value of the height of the first side face portion;
• the third side face portion has a negative clearance angle such that the third side face portion is parallel to the center axis, and in a side view, a height of the third side face portion, in the center axis direction, increases in the direction of approaching from the corner cutting edge to the main cutting edge.