Turning tool with interchangeable polygonal cutting insert

In a turning tool having an interchangeable polygonally shaped cutting insert, particularly for metal machining, the improvement comprising:

• a holder having a first recess therein;
• an insert carrier received in said first recess and secured thereto by means of a holding screw, said insert carrier having a second recess therein for receiving said cutting insert therein;
• first holding means for holding said cutting insert in said second recess, said insert carrier having a planar base face and a generally semicylindrical supporting surface extending at right-angles to said base face, said semicylindrical supporting surface extending continuously between said base face and an opposite face on said insert carrier on its edge facing away from an effective cutting point on said cutting insert, said base face and said semicylindrical supporting surface on said insert carrier being supported on correspondingly shaped counter-surfaces of said first recess, one of said counter-surfaces being a semicylindrical support surface, said insert carrier having a first threaded central hole therein for receiving said first holding means therein, the axis (A) of said semicylindrical supporting surface on said insert carrier coinciding generally with the axis (A) of said central hole, said semi-cylindrical supporting surface having a radius (R) only slightly greater than a distance (a) between said effective cutting point and said axis (A) of said central hole, said supporting surface on said insert carrier having in its central region a smaller radius portion than said radius (R), the circumferentially spaced portions of said supporting surface on said insert carrier having the larger radiused surface engaging said semicylindrically shaped counter-surface on said holder;
• second holding means for holding said insert carrier to said holder in said first recess;
• a second threaded hole in said insert carrier extending parallel to said first threaded hole and perpendicular to said base face, said first holding means comprising a first screw received in said first threaded hole, said second holding means comprising a second screw received in said second threaded hole;
• said insert carrier having a fixing bore extending perpendicular to said base face and a fixing pin received in said fixing bore and a corresponding bore in said first recess, said fixing bore being provided at a point remote from said axis (A) of said semicylindrical supporting surface and at the point of intersection of two bearing faces which include an angle of somewhat less than 90.degree., said two bearing faces being provided opposite said effective cutting point with a third bearing face being provided adjacent an effective cutting edge.