STEP 4. SELECT INSERT SHAPES
Indexable inserts (Figure F-35), also called throw away inserts. Are clamped in toolholders of various design. These inserts provide a cutting tool with several cutting edges. After all edge have been used, the insert is discarded.
The round inserts have the greatest strength and, as with large radius inserts, make possible higher feed rates with equal finishes. Round inserts also have the greatest number of cutting edges possible, but are limited to work piece configuration and operation that are not affected by a large radius. Round inserts would be ideally suited, for example, to straight turning operations.
Square inserts have lower strength and fewer possible cutting edges than round tools, but are much stronger than triangular inserts. The included angle between cutting edge (90 degrees) is greater than that for triangular inserts (60 degree), and there are eight cutting edge possible compared to six for the triangular inserts.
Triangular inserts have the greatest versatility. They can be used, for example, for combination turning and facing operations, while round or square inserts are often not adaptable to such combinations. Because the included angle between cutting edge is less than 90 degrees, the triangular inserts are also capable of tracing operation. The disadvantages include their reduced strength and fewer cutting edge per insert.
For tracing operations where triangular inserts cannot be applied, diamond-shaped inserts with smaller included angles between edges
are available. The included angles on these diamond shaped inserts range from 35 to 80 degrees. The smaller angle inserts in particular may be plunged into the workpiece as required for tracing. A typical setup for tracing is shown in Figure F-36. Note that small clearance angles are used for each cutting edge to permit plunging.