Cutting insert and cutting tool equipped therewith

1. A cutting insert comprising:

an upper surface, which is a first end surface;

a lower surface, which is a surface on an opposite side to the upper surface, and is a second end surface having an installing surface for installing a cutting tool to a body;

a screw hole which has an axial line, which is a center axis of the cutting insert, penetrating from the upper surface to the lower surface;

a peripheral side surface which is formed such that the upper surface and the lower surface are connected;

a major cutting edge and an inner cutting edge which are formed in an intersecting region between the upper surface and the peripheral side surface, and an intersecting region between the lower surface and the peripheral side surface, respectively;

a constraining surface which is formed on the peripheral side surface so as to at least partially contact with the body; and

an R region which has a convex shape and is formed between the major cutting edge and the inner cutting edge at a position closer to the inner cutting edge than a first axial line perpendicular to and intersecting the center axis at a center point equidistant from the upper surface and the lower surface, and passing through a center of the peripheral side surface below the intersecting region between the upper surface and the peripheral side surface, wherein

an inclination angle of a linear portion of the major cutting edge with respect to a second axial line perpendicular to and intersecting the center axis at the center point and perpendicular to the first axial line, and an inclination angle of the constraining surface with respect to the second axial line, are different in a top view viewed from the upper surface,

the inclination angle of the major cutting edge is smaller than the inclination angle of the constraining surface, and

a first virtual cross-section sectioned at a virtual surface, which is vertical to the installing surface of the lower surface and passes through the major cutting edge of the upper surface, is shaped such that the constraining surface is farther from the center axis of the cutting insert than a flank of the major cutting edge of the upper surface in a first direction along the first axial line by a first length difference, and an inner cutting edge of the lower surface is farther from the center axis of the cutting insert than the constraining surface in the first direction of the first axial line by a second length difference.

2. The cutting insert according to claim 1 , wherein

in the top view, the inner cutting edge of the lower surface is located farther from the second axial line than the major cutting edge of the upper surface.

3. The cutting insert according to claim 1 , wherein

the inclination angle of the major cutting edge and an inclination angle of the inner cutting edge with respect to the second axial line are different in the top view, and the inclination angle of the major cutting edge is smaller than the inclination angle of the inner cutting edge.

4. The cutting insert according to claim 3 , wherein

the inclination angle of the inner cutting edge and the inclination angle of the constraining surface are the same in the top view.

5. The cutting insert according to claim 1 , wherein

in a side view viewing the side surface on which the constraining surface is formed, the major cutting edge of the upper surface is formed at a height intersecting with an installing surface formed on the upper surface for installing a cutting tool to the body so as to be inclined with respect to the installing surface, and the inner cutting edge of the upper surface is formed at a lower position than the installing surface.

6. The cutting insert according to claim 1 , wherein

on the first virtual cross-section sectioned at the virtual surface which is vertical to the installing surface of the lower surface and passes through the major cutting edge of the upper surface, the flank of the major cutting edge is a surface of which a clearance angle is 0° or a negative value, and

on a second virtual cross-section sectioned at a virtual surface which is vertical to the installing surface of the lower surface and passes through the inner cutting edge of the upper surface, a flank of the inner cutting edge is a positive surface of which a clearance angle is a positive value.

7. A cutting tool comprising:

a body which rotates around a rotation axis and includes an insert seat for holding a cutting insert; and

the cutting insert according to claim 1 , which is installed in the body such that the installing surface of the lower surface contacts with the insert seat.