Korloy Turning Insert Family Guide: Matching DNMG, WNMG, CNMG, SNMG and TNMG to Your Application

Choosing the correct turning insert geometry is one of the most impactful decisions a CNC programmer or operator can make. The ISO designation system tells you far more than just the shape of the insert; it encodes clearance angles, tolerances, hole styles, and cutting-edge lengths that directly influence chip control, surface finish, and tool life. Korloy manufactures a comprehensive range of turning inserts covering every major ISO family, and understanding when to reach for a DNMG versus a WNMG can cut cycle time and reduce scrap rates dramatically. This guide walks through the five most common turning insert families in the Korloy catalog and explains how to match each one to real-world materials and operations.

Understanding the ISO Turning Insert Code

Before selecting a family, it is worth recalling what the first letter in an ISO code represents. The insert shape determines the number of cutting edges available and the strength of the corners. A larger included angle, such as the 80 degrees found in CNMG and DNMG inserts, offers a stronger corner but requires more machine power. A smaller included angle, such as the 60 degrees of TNMG or TNMG, provides lower cutting forces and better accessibility in tight features but sacrifices some edge robustness. The second letter indicates relief angle: N for 0 degrees (double-sided, negative inserts) and M for 7 degrees (single-sided, neutral inserts). Negative inserts are the default for most roughing and general turning because they provide twice the number of edges and better seat stability.

CNMG: The All-Rounder for Roughing and General Turning

The 80-degree rhombus shape of the CNMG family makes it the workhorse of external turning. Its strong corner geometry handles heavy depths of cut and high feed rates without chipping, which is why it dominates steel and cast iron applications. Korloy offers CNMG inserts in grades ranging from the general-purpose PC5300 PVD-coated grade through to the CVD-coated PC8110 for high-speed finishing in steels.

For medium roughing of carbon steel at a depth of cut between 2 mm and 4 mm, a CNMG 120408-HM grade PC5300 running at 220 m/min with a feed of 0.25 mm/rev delivers predictable tool life and excellent chip breaking. If you are working with stainless steel 304 or 316L, switching to the PC9530 grade with the HS chipbreaker allows you to maintain 180 m/min while resisting the built-up edge that plagues austenitic materials. The CNMG shape is less suited to profiling operations where the nose radius interferes with fine details, but for straight turning, facing, and heavy roughing, it is difficult to beat.

WNMG: Stronger Corners for Interrupted Cuts and Cast Iron

The WNMG family uses an 80-degree trigonal shape with a truncated corner. Compared to CNMG, the WNMG offers a slightly wider cutting edge relative to its inscribed circle, which translates into better heat dissipation and a stronger seat in the tool holder. This makes WNMG inserts a natural choice for interrupted cuts, scale-covered forgings, and nodular cast iron where mechanical shock is a constant threat.

Korloy’s WNMG 080408-HM paired with the PC8110 CVD grade is an excellent starting point for roughing grey cast iron at 150 m/min and 0.3 mm/rev feed. The wider body of the insert helps stabilize the cut when passing through sand inclusions or hard spots. In automotive applications machining brake discs or flywheels, operators often report 15 to 20 percent longer tool life when switching from CNMG to WNMG under identical parameters, simply because the insert geometry distributes impact forces more evenly across the seat.

DNMG: Precision and Accessibility for Profiling and Finishing

The 55-degree rhombus of the DNMG family narrows the nose angle compared to CNMG, giving the insert better reach into shoulders, tapers, and complex profiles. While the corner is inherently less strong than an 80-degree shape, modern coatings and substrates have narrowed the durability gap significantly. The DNMG family shines in finishing passes where surface quality and dimensional accuracy take priority over material removal rate.

For finish turning of mild steel with a 0.5 mm depth of cut and 0.1 mm/rev feed, a DNMG 150604-MM grade PC5300 produces Ra values below 1.6 micrometers without requiring a separate wiper insert. In stainless steel finishing, the DNMG 110408-NM with Korloy’s PC9530 grade offers a good balance between chip control and edge sharpness. Because the DNMG shape is also popular for copy turning, it is worth keeping a selection of nose radii on hand: 0.4 mm for fine finishing, 0.8 mm for general purpose, and 1.2 mm when a slightly stronger corner is needed for semi-finishing.

SNMG: Square Inserts for Maximum Edge Economy

Square inserts provide the highest number of cutting edges per insert, making them the economical choice for high-volume production where tooling cost per edge matters. The SNMG family is commonly used for face turning, plunge roughing, and operations where the tool approaches the work at 90 degrees. The 90-degree entering angle of an SNMG tool holder produces a square shoulder, which is useful when a clean 90-degree wall is required without a secondary operation.

Korloy SNMG 120408-HM inserts in grade PC8110 are a reliable choice for roughing large-diameter shafts in low-alloy steel. At 200 m/min and 0.35 mm/rev, the square geometry maintains stability even at depths of cut up to 5 mm. One practical tip: because the SNMG nose radius is positioned at the corner of a square, the effective cutting edge length is longer than it appears on paper. This means you can often increase feed rate by 10 to 15 percent compared to a CNMG of the same inscribed circle size without sacrificing chip control.

TNMG: Low Cutting Forces for Small Parts and Exotics

The 60-degree triangular TNMG family offers the lowest cutting resistance of the major negative-insert shapes. This makes TNMG inserts ideal for small-diameter work where spindle power is limited, for slender shafts where deflection must be minimized, and for gummy materials like titanium and copper alloys that benefit from a free-cutting geometry. The trade-off is reduced corner strength, so TNMG inserts are rarely the first choice for heavy roughing of hardened materials.

In titanium Ti-6Al-4V turning, a TNMG 160404-HS grade PC2510 running at 40 m/min with 0.12 mm/rev feed keeps cutting temperatures lower than a CNMG equivalent because the reduced contact length generates less frictional heat. For copper alloy machining, the same TNMG geometry in an uncoated or minimally coated grade prevents built-up edge while delivering mirror-like surface finishes. Korloy also produces positive-angle TPMT and TPGB variants for ultra-light finishing, but for general-purpose small-part turning, the TNMG remains the most versatile choice.

Quick Reference: Matching Insert Family to Operation

Final Recommendations

No single insert family handles every turning operation optimally. A well-stocked tool crib should include CNMG and WNMG inserts for heavy material removal, DNMG inserts for profiling and finishing, and TNMG inserts for exotic materials and small components. When evaluating Korloy inserts, pay attention not only to the shape but also to the chipbreaker code and grade. The HM breaker is aggressive for roughing, the MM breaker is balanced for medium machining, and the NM or HS breakers are tuned for finishing and stainless or titanium work. Pairing the right geometry with the right grade is what separates an average setup from a highly productive one.