Cutting insert and cutter

An insert cutter comprising:

• a tool body having an axis of rotation therethrough;
• and
• a cutting insert including a polygonal plate-shaped insert body having two opposite faces directed in a direction of insert thickness and a plurality of peripheral faces disposed between said opposite faces, said insert being releasably attached to said tool body so that said opposite faces are directed radially of said tool body, said opposite faces having marginal edges with at least one of said marginal edges defining a main cutting edge, said peripheral faces intersecting one another to from marginal edges with at least one of said marginal edges defining an auxiliary cutting edge which intersects said main cutting edge, a peripheral face which intersects the marginal edges defining said main and auxiliary cutting edges including a rake region extending along said main and auxiliary cutting edges, said insert body having a nose portion into which said main cutting edge and said auxiliary cutting edge merge,
• said rake region comprising a plurality of sections, each said section being disposed in a plane different from another section, said sections intersecting one another to define marginal edges at intersections thereof and terminating at one end at said main cutting edge, said rake region being convexly shaped in such a manner that an included angle defined by a respective section and one of said opposite faces which extends from said main cutting edge decreases with distance from said nose portion, at least one of said marginal edges of said sections having the other end extending to a marginal edge defined between said peripheral faces.