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.

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.

In order to easily disposed a projection by accurately inspecting and measuring (correcting) a position of the projection relative to the cutting edge, and to improve the chip control regardless the insert shape by optimizing the disposition of the projection, the present invention provides a cutting tool including: an upper surface; a lower surface; a side surface; a cutting edge including a pair of major cutting edges and a corner cutting edge; a first upper surface; a second upper surface; an inclined surface; a groove disposed in the second upper surface; and a first projection and a second projection which are formed to be projected from the inclined surface. The first projection extends on the groove along the extended line, and the second projection is disposed to be linearly symmetric with respect to the extended line. At an intersection between the corner cutting edge and the bisector in a top view, L1<L2 is established, where L1 is a distance from a virtual line intersecting perpendicularly to the bisector to a leading end of the first projection, and L2 is a distance from the virtual line to a leading end of the second projection.