There are many variables that go into choosing the correct insert for your turning operations: insert shape, geometry, grade, and more. The goal is to select an insert that meets your requirements for quality and performance, while providing good chip control, and a reasonable combination of wear resistance and toughness.
Choose the insert style (shape and size) based on the features of the part and the desired depth of cut. A larger nose radius is stronger, but requires more machine power, and increases the tendency for vibration. A smaller nose radius increases the access to fine part features, but has a weaker cutting edge.
Choose the chip breaker (geometry) based on the selected machining operation: finishing, medium, or roughing. Roughing with high depths of cut and feedrates requires an insert with a stronger cutting edge. Finishing operations with light depths of cut and lower feedrates produce lower cutting forces, so cutting-edge strength is not as important. Medium turning operations, with a wide range of depths of cut and feedrate, require a more versatile geometry.
Choose the insert grade (coatings) based on the type of material being cut, the specific machining operation (finishing, medium, roughing), and the cutting conditions (smooth, lightly interrupted, heavily interrupted). The insert grade and the chip breaker complement each other to provide specific performance characteristics. A tougher grade can compensate for a cutting edge with less strength, while a more wear resistant grade can provide longer tool life on a stronger cutting edge.