Tooling Fundamentals: Selecting Inserts and Holders for Optimal CNC Turning

The cutting tool is the point of contact between machine and material. Correct selection is critical for finish, tool life, and cost per part.

1. Insert Geometry & Grade:​ The insert’s shape (diamond, square, round, etc.) and coating (TiN, TiAlN, Al2O3, etc.) are chosen for the operation and workpiece material.

• Geometry:​ A sharp, positive-rake insert is for finishing aluminum. A robust, negative-rake insert is for heavy roughing on steel.
• Grade:​ Select a grade designed for your material group (P for steel, M for stainless, K for cast iron, N for non-ferrous).

2. Insert Nomenclature:​ Learn to read the ISO code (e.g., CNMG 432). It defines shape, relief angle, tolerance, type, size, thickness, and nose radius.

3. Tool Holders:​ The holder provides the interface between the turret and the insert. Key choices are:

• Style:​ Turning (external), boring (internal), threading, grooving, or profiling.
• Clamping Mechanism:​ Top-clamp, screw-down, or wedge-clamp. Each offers different levels of rigidity and insert accessibility.
• Lead Angle:​ The direction the cutting force is applied (e.g., 93°, 45°). This affects chip control and radial/axial force direction.

Best Practice:​ Partner with a reputable tooling supplier. They can provide application-specific recommendations, optimize speeds/feeds, and help you standardize tooling to reduce inventory and setup time.