A cutting insert includes an upper surface and upper edge. The upper surface includes a second side part, a first corner part, and a second corner part. The upper surface further includes a first surface and a second surface. The upper edge includes a first edge located at the first corner part, a second edge located at the second side part, and a third edge located at the second corner part. The second surface includes a first region extending toward the first corner part, and a second region extending toward the second corner part. A distance between the first region and the upper edge is smaller at a side of the second edge than at a side of the first edge. A distance between the second region and the upper edge is smaller at a side of the second edge than at a side of the third edge.

A cutting tool according to an aspect of the present invention is a cutting tool for cutting a rotationally symmetrical surface of a rotating workpiece. The cutting includes the step of feeding the cutting tool in a direction inclined with respect to a rotational axis of the rotationally symmetrical surface, while holding the cutting tool in contact with the rotationally symmetrical surface. In the step of feeding the cutting tool, the cutting tool has a point that is in contact with the rotationally symmetrical surface and the point shifts as the cutting tool is fed. The cutting tool includes: a rake face; a flank face; and a cutting edge connecting the rake face and the flank face. The cutting edge as seen from above the flank face has a shape including at least one arc, and the arc has a radius of curvature of not less than 100 mm and not more than 500 mm.

A cutting insert includes an upper surface and upper edge. The upper surface includes a second side part, a first corner part, and a second corner part. The upper surface further includes a first surface and a second surface. The upper edge includes a first edge located at the first corner part, a second edge located at the second side part, and a third edge located at the second corner part. The second surface includes a first region extending toward the first corner part, and a second region extending toward the second corner part. A distance between the first region and the upper edge is smaller at a side of the second edge than at a side of the first edge. A distance between the second region and the upper edge is smaller at a side of the second edge than at a side of the third edge.

A cutting tool for cutting a rotationally symmetrical surface of a rotating workpiece includes the step of feeding the cutting tool in a direction inclined with respect to a rotational axis of the rotationally symmetrical surface, while holding the cutting tool in contact with the rotationally symmetrical surface. In the step of feeding the cutting tool, the cutting tool has a point that is in contact with the rotationally symmetrical surface and the point shifts as the cutting tool is fed. The cutting tool includes: a rake face; a flank face; and a cutting edge connecting the rake face and the flank face. The cutting edge as seen from above the flank face has a shape including at least one arc, and the arc has a radius of curvature of not less than 100 mm and not more than 500 mm.

A cutting insert includes a top face, a bottom face and a plurality of side walls extending between the top face and the bottom face. A peripheral cutting edge is defined at the juncture of each side wall and the top face. Each cutting edge includes a linear cutting edge portion and a concave cutting edge portion that curves inwardly in a plane that is perpendicular to a plane containing a central axis of the cutting insert. A radiused corner portion connects two adjacent cutting edges. Each linear cutting edge portion extends from one radiused corner portion to the concave cutting edge portion and the concave cutting edge portion extends from the linear cutting edge portion to another radiused corner portion.