Throwaway insert and cutting tool having throwaway insert

A throwaway insert comprising:

• a cutting face as an upper surface thereof;
• an attaching surface as a lower surface thereof for attaching to a tool main body;
• a flank as a side surface thereof formed between the cutting face and the attaching surface;
• and
• a major cutting edge which is formed along an intersecting ridge between the cutting face and the flank, and which includes a curved cutting edge,
• wherein the curved cutting edge is formed so as to extend along an imaginary cylindrical surface whose center axis coincides with the axis of rotation of the tool main body, as viewed in a state in which the throwaway insert is attached to the tool main body, and
• wherein the curved cutting edge is formed along a convex curve projecting in the direction of rotation of the tool main body when viewed in a radial direction of the tool main body, and is formed such that the distance from the attaching surface gradually decreases as the distance from a proximal end of the tool main body decreases.

A cutting tool comprising:

• a tool main body, wherein the surface roughness of a distal end of the tool main body is less than 3.2 μm when indicated by the Ry roughness;
• and
• a throwaway insert provided at the distal end of the tool main body;
• wherein the throwaway insert is substantially formed in a polygonal shape and the throwaway insert includes:
• a cutting face as an upper surface thereof;
• an attaching surface as a lower surface thereof for attaching to a tool main body;
• a flank as a side surface thereof formed between the cutting face and the attaching surface;
• a nose portion which is formed at a corner of the cutting face, and which has a substantially arc-shaped cutting edge;
• and
• a major cutting edge which is formed along an intersecting ridge between the cutting face and the flank so as to be connected to an end of the cutting edge of the nose portion, and which includes a tapered cutting edge connected to the cutting edge of the nose portion, and a curved cutting edge connected to an end of the tapered cutting edge at a connection point positioned opposite to the nose portion,
• wherein the curved cutting edge is formed so as to extend along an imaginary cylindrical surface whose center axis coincides with the axis of rotation of the tool main body, as viewed in a state in which the throwaway insert is attached to the tool main body in such a manner that the nose portion is positioned at an outer periphery of a distal end of the tool main body, and wherein the tapered cutting edge is formed so as to gradually curve from the imaginary cylindrical surface toward the inside of the imaginary cylindrical surface as the distance from the curved cutting edge increases, and the distance from the nose portion decreases.