An indexable cutting tip, usually coated carbide, in a standard shape such as diamond, triangle, square or round, clamped in a turning, milling or drilling holder. Each corner is a cutting edge, and when one wears the insert is turned, or indexed, to the next. Inserts are identified by a standard code that gives shape, clearance, tolerance, hole and chipbreaker type, size, thickness and nose radius, such as CNMG 432 in inch or CNMG 120408 in metric.
Index the insert, that corner's done, and if all four are gone, grab a new box of CNMGs from the crib.
Read the chipbreaker code as carefully as the shape; the wrong breaker turns a good cut into a bird's nest.
Also heard as
- carbide insert
- indexable insert
- tip
Related terms
Built-up edge
Work material welded onto the cutting edge, which changes the tool's shape and tears the surface finish.
Blue chips
Steel chips that come off straw to dark blue from heat, read as a sign of how hard a cut is running.
Bird's nest
A tangled wad of long, stringy chips wrapped around the tool, chuck or part on a lathe.
Tool crib
The controlled storeroom where a shop keeps cutters, inserts, gauges and shared tools, checked out by request.