Turning Insert Grade Selection

A practical guide to choosing the right carbide grade for your turning application.

Selecting the right insert grade is one of the most impactful decisions in turning operations. The wrong grade causes poor surface finish, rapid tool wear, or catastrophic insert failure. This guide covers the standard ISO application groups and how to choose between them.

ISO Application Groups

The ISO standard divides carbide grades into three main application groups based on workpiece material:

• P Group (Steel): For machining steel, steel castings, and long-chipping malleable cast iron. Grades with higher toughness and TiAlN/CVD coatings.
• M Group (Stainless): For austenitic stainless, duplex, and super-martensitic grades. Requires sharp edges and heat-resistant coatings like AlTiN.
• K Group (Cast Iron): For gray iron, ductile iron, and chilled iron. Uncoated or TiCN coated grades with high thermal conductivity.
• N Group (Non-Ferrous): For aluminum, copper, and plastics. Polished surface grades with sharp edges, typically uncoated.
• S Group (Superalloys): For titanium, Inconel, and heat-resistant alloys. Submicron grades with TiSiN or AlCrN coatings.
• H Group (Hardened): For hardened steel above HRC 45. CBN (cubic boron nitride) or ceramic grades recommended.

Grade Selection by Material

Common Insert Geometries

• CNMG: 80° diamond, most versatile for general turning. Available in all grades.
• WNMG: 80° trigon, strong cutting edge for roughing.
• TNMG: 60° triangle, good for heavy feeds and roughing.
• DCMT: 55° diamond, for finishing and small parts.
• VBMT: 35° diamond, for profiling and finishing narrow areas.