A turning tool includes: a holder portion; and a cutting edge portion fixed to the holder portion, wherein the cutting edge portion is composed of a synthetic single-crystal diamond, and the cutting edge portion has a nose curvature having a curvature radius of more than or equal to 0.1 mm and less than or equal to 1.2 mm, and the nose curvature satisfies at least one of a condition that a direction of a line of intersection between the rake face and a bisecting cross section of a vertex angle of the nose curvature is within 10 relative to a <110> direction of the synthetic single-crystal diamond, and a condition that the direction of the line of intersection between the rake face and the bisecting cross section of the vertex angle of the nose curvature is within 10 relative to a <100> direction of the synthetic single-crystal diamond.

A cutting insert in a non-limiting embodiment may include a first surface, a second surface, a third surface and a land surface. The first surface may include a first corner and a first side extended from the first corner. The land surface may be located between the first surface and the third surface and inclined relative to the first surface and the third surface. The land surface may include a first land surface located along the first corner, a second land surface located along the first side, and a third land surface having a concave shape which is adjacent to the second land surface and located further away from the first land surface than the second land surface.

A cutting insert may include a first surface, a second surface, a third surface, and a land surface. The first surface may include a first corner, a first side, and a second side. The land surface may be inclined relative to the first surface and the third surface. The land surface may include a first land surface connecting to the first corner. An imaginary flat surface orthogonal to a central axis connecting a center of the first surface and a center of the second surface may be a reference plane, a first inclination angle of a part of the first land surface which connects to a midportion of the first corner may be larger than a second inclination angle of a part of the first land surface which connects to an end portion at a side of the first side of the first corner.

A turning insert includes a head portion connected to a stem portion. A CBN cutting edge includes a surface generating cutting edge and two major cutting edge portions, such that each major cutting edge portion forms an angle of 5-20 in relation to a tangent line of the cutting edge at a forward point of the cutting edge.

A cutting edge includes a nose portion, a first cutting edge portion, and a second cutting edge portion. When a boundary between a first inclined portion and a first breaker portion, a boundary between a first step surface and a second breaker portion, a boundary between a second inclined portion and a third breaker portion, and a boundary between a second step surface and a fourth breaker portion are a first position, a second position, a third position, and a fourth position, respectively, the second position is higher than the first position and the fourth position is higher than the third position in a direction perpendicular to the seating surface, and a distance between the first position and the third position is greater than a distance between the second position and the fourth position in a direction parallel to the seating surface.

A turning insert has two opposite main surfaces and a peripheral surface which extends therebetween and has N side surfaces, where 2<N<9. The insert has mirror symmetry about a mid-plane and 360/N degree rotational symmetry about a central axis perpendicular to the mid-plane. The insert has two main edges which each have N main cutting edges and N corner cutting edges. Each main cutting edge has two raised edge portions and a lowered edge portion. Each main surface has N main rake surfaces and N corner rake surfaces. Each main surface further has at least N convex island protrusions and N at least partially convex peninsula protrusions, any and all island protrusions associated with a given main rake surface being located between two adjacent peninsula protrusions, each pair of adjacent peninsula protrusions having at least one island protrusion located therebetween.

An insert includes a first surface having a corner portion, a second surface, a third surface, and a cutting edge. The cutting edge is provided with a first cutting edge located on the corner portion and a second cutting edge adjacent to the first cutting edge, and the third surface is provided with a first portion located along the first cutting edge and a second portion located along the second cutting edge. the second portion includes a first region having a first end portion and a second end portion, and a second region having a third end portion and a fourth end portion. An inclination angle 212 at the second end portion is greater than an inclination angle 211 at the first end portion, and an inclination angle 222 at the fourth end portion is smaller than an inclination angle 221 at the third end portion.

A cutting insert according to an aspect includes a top surface and a side surface. At least a part of a ridge line where the top surface and the side surface intersects is a cutting edge. The cutting edge includes a first portion located at a corner portion, a second portion adjacent to the first portion, a third portion close to the second portion, a fourth portion close to the third portion, and a fifth portion adjacent to the fourth portion. When viewed from directly above, a curvature radius of the second portion is less than a curvature radius of the first portion, a curvature radius of the third portion is greater than the curvature radius of the first portion, and a curvature radius of the fourth portion is less than the curvature radius of the third portion.

The invention discloses a wheel machining tool. A rough turning tool and a finish turning tool are respectively arranged on two sides of a tool head, the primary declination angle of the rough turning tool is set to 90 to 120, and the primary declination angle of the finish turning tool is set to 85 to 95; the axial height difference between the rough turning tool and the finish turning tool is set to 0.2-0.5 mm; the distance c between the rough turning tool and the tool head is set to 5-8 mm, and the distance b between the finish turning tool and the tool head is set to 3-5 mm. The rake angle of the rough turning tool is set to 12-15, the rake angle of the finish turning tool is set to 14-17.

A turning insert arranged for longitudinal turning of metal work pieces includes a nose cutting edge that slopes from a trailing cutting edge in direction towards a leading cutting edge. A turning tool is also disclosed.