CNMG vs DNMG vs WNMG Turning Inserts: Shape, Strength, and Application Guide

Turning inserts come in standardized ISO shapes, and the three most common — CNMG, DNMG, and WNMG — each serve different purposes based on their geometry, cutting edge strength, and chip control characteristics. Understanding the differences is essential for optimizing tool life, surface finish, and cutting forces in CNC turning operations.

1. ISO Insert Designation Decoded

Before comparing the three shapes, let’s decode the ISO insert designation. Taking CNMG120408 as an example:

• C = Insert shape (C = 80° rhombic, D = 55° rhombic, W = 80° trigon)
• N = Clearance angle (N = 0°, negative rake; A/B = 20°/positive)
• M = Tolerance class (M = medium ±0.08 mm, G = precision ±0.025 mm)
• G = Chipbreaker type and hole (G = with hole and chipbreaker on top)
• 12 = Cutting edge length (12 mm)
• 04 = Insert thickness (4.76 mm)
• 08 = Nose radius (0.8 mm)

2. Shape Comparison at a Glance

3. CNMG: The General-Purpose Workhorse

The CNMG 80° rhombic insert is the most widely used turning insert worldwide. Its 80° included angle provides a strong cutting edge capable of handling both roughing and finishing on the outer diameter. The four usable edges give good economy, and the shape is compatible with a wide range of standard toolholders (PCLNR, PTJNR, MCLNR).

Strengths:

• Strong 80° cutting point handles interrupted cuts and hard spots
• Available in all major sizes: 09, 12, 16, and 19 (edge lengths 9.5–19 mm)
• Huge selection of chipbreakers: Korloy offers 8+ chipbreaker geometries for CNMG, from light finishing (-LF) to heavy roughing (-HR)
• Standard for OD turning in carbon steel, alloy steel, and cast iron

Limitations: Cannot machine shoulders tighter than 80° (leaving a 10° draft). The 80° point limits profile turning capability compared to DNMG.

The Korloy CNMG120408-MA (medium chipbreaker, NC3220 grade) is one of the best-selling turning inserts globally — a default choice for general steel turning at 180–250 m/min with 0.2–0.4 mm/rev feed.

4. DNMG: The Profile Specialist

The DNMG 55° rhombic insert’s narrow included angle gives it superior accessibility for profile turning, contouring, and machining features near shoulders or steps. The 55° point can reach into features that an 80° insert cannot access.

Strengths:

• 55° point allows contouring and profile work with minimal clearance requirements
• Lower radial cutting force (force directed more axially) — excellent for thin-walled and slender parts
• Standard for copy turning, ball turning, and complex profiles on CNC lathes
• Common in Swiss-type lathes and compact turning centers where space is limited

Limitations: The 55° point is inherently weaker than an 80° point. It is more prone to chipping in heavy interrupted cuts and hard materials. Not suitable for heavy roughing in steel above 4 mm depth of cut.

Korloy DNMG150408 inserts in the NC3020 grade (PVD-coated for sharpness) are the go-to choice for stainless steel finish turning where the 55° geometry’s lower cutting forces prevent work hardening and chatter.

5. WNMG: The Economy Champion

The WNMG 80° trigon (triangular with truncated corners) offers six usable cutting edges — 50% more than CNMG or DNMG — making it the most economical insert per cutting edge. The trigon shape also provides a slightly wider cutting edge than CNMG at the same included angle, contributing to improved edge strength.

Strengths:

• Six cutting edges per insert — lowest cost per edge in production turning
• 80° point strength comparable to CNMG
• Excellent for high-volume production where insert consumption is a major cost factor
• Widely used in automotive transmission and engine component machining

Limitations: The trigon shape is thicker than CNMG, requiring slightly more clamping force. Toolholder options are more limited — primarily MWLNR and PWLNR types. Less common in job shops compared to CNMG.

6. Nose Radius: The Shared Parameter

All three shapes share the same nose radius options, which directly affect surface finish and cutting forces:

The theoretical surface finish formula Ra = f²/(32 × r) shows that halving the feed rate or doubling the nose radius both reduce Ra by 4×. In practice, real finishes are 2–3× worse than theoretical due to built-up edge, machine condition, and material variability.

7. Decision Framework

1. Profile complexity: Simple OD turning → CNMG. Contour/profile work → DNMG. High-volume simple OD → WNMG for economy.
2. Edge strength requirement: Interrupted cuts, hard materials → CNMG or WNMG (80°). Continuous cuts only → DNMG acceptable.
3. Production volume: High volume (>5,000 parts) → WNMG (6 edges). Medium volume → CNMG (widest chipbreaker selection). Low volume → DNMG for flexibility.
4. Machine condition: Older machines with more vibration → CNMG with larger nose radius. Rigid new machines → DNMG with smaller nose radius for better finish.
5. Toolholder inventory: If your shop is standardized on PCLNR/PTJNR holders → CNMG. MWLNR holders → WNMG. PDJNR holders → DNMG.

8. Grade Recommendations by Insert Shape

Summary

CNMG, DNMG, and WNMG serve different niches in CNC turning. CNMG is the versatile general-purpose insert. DNMG excels in profile turning and contouring where accessibility is critical. WNMG delivers the lowest cost per cutting edge in high-volume production. Nose radius, chipbreaker, and grade selection further optimize each shape for the specific application.

Stock up on Korloy CNMG, DNMG, and WNMG inserts in all sizes and grades at hooguu.com — bulk pricing, fast shipping, and the technical support your turning operation needs.