Indexable insert

1. An indexable insert having two main faces that face away from one another, wherein each face has a full-perimeter cutting edge, a chip step adjoining the cutting edge and having a continuously curved surface, a chip forming element disposed in the chip step, the chip forming element having a run-on face, a transverse rib protruding therefrom, and a spacing groove disposed between the chip forming element and a central bearing contact region.

2. The insert as claimed in claim 1 , wherein the chip step further comprises an inlet region having a plurality of radii of curvature (R 1 ) that become smaller as the distance from the cutting edge increases, and further comprising an outlet region that adjoins the inlet region and has a plurality of radii of curvature (R 2 , R 3 ) that become incrementally larger.

3. The insert as claimed in claim 2 , wherein the plurality of radii of curvature (R 2 , R 3 ) of the outlet region of the chip step graduate tangentially into one another.

4. The insert as claimed in claim 1 , wherein the chip step further comprises an inlet region having a radius of curvature (R) that becomes continuously smaller and an outlet region having a radius of curvature (R) that becomes continuously larger.

5. The insert as claimed in claim 4 , wherein the inlet region graduates into outlet region at the lowest point of the inlet region.

6. The insert as claimed in claim 1 , wherein the run-on face of the chip forming element has a curved surface with a radius of curvature (R) that decreases progressively as the distance from the cutting edge increases.

7. The insert as claimed in claim 1 , wherein the central bearing contact region divided by intermediate channels into a multiplicity of bearing contact frustums.

8. The insert as claimed in claim 1 , wherein the central through bore has a bore periphery rising toward the bore.