Korloy Chipbreaker Codes Decoded: HM, HS, MM, HMP and NM Explained

Every Korloy turning insert carries a two or three-letter chipbreaker suffix that defines its mechanical personality. This code determines the feed range, depth of cut capability, chip control behavior, and cutting force characteristics of the insert. Choosing the wrong chipbreaker is as costly as choosing the wrong grade: you might get acceptable tool life but terrible chip control, or perfect chips but premature edge failure from exceeding the chipbreaker’s structural limits.

This article decodes the five core Korloy chipbreaker geometries and provides practical guidance for selection based on your actual cutting conditions.

The Role of Chipbreaker Geometry

A chipbreaker is not simply a “chip breaking” feature. The geometry of the rake face, the width of the land, the entry angle of the chip groove, and the height of the backwall collectively determine four critical outcomes: cutting force magnitude, chip curl radius, chip flow direction, and edge strength. These factors interact with feed rate and depth of cut to produce either controlled C-shaped or helical chips (ideal), or problematic bird’s nests, long strings, or snarling ribbons.

Korloy’s coding system maps five distinct geometries to five overlapping application zones, creating a complete system from heavy roughing to precision finishing.

HM – Heavy Medium Roughing

Specifications

Feed range: 0.25-0.55 mm/rev. Depth of cut: 1.5-7.0 mm. Target: General roughing of carbon and alloy steels where maximum material removal is the priority.

Geometry Characteristics

The HM chipbreaker features a wide negative land (0.15-0.20 mm) that provides exceptional edge strength, followed by a moderately deep chip groove with a pronounced backwall. This combination generates enough chip curl to break chips reliably at heavy feeds while the reinforced edge resists the mechanical impact of interrupted cuts and scale on forged blanks.

The land angle on HM is typically 15-20 degrees negative, creating a strong cutting edge that can absorb the cyclical loading of interrupted turning. The trade-off is higher cutting forces compared to positive geometries, requiring adequate machine power and workpiece rigidity.

When to Use HM

HM is your default roughing chipbreaker for steel turning operations where DOC exceeds 1.5 mm and feed exceeds 0.25 mm/rev. It excels on hot-rolled bar stock, forgings with scale, and any situation where edge security matters more than cutting force reduction.

HS – Heavy Steel (Extended Depth)

Specifications

Feed range: 0.25-0.50 mm/rev. Depth of cut: 2.0-9.0 mm. Target: Heavy stock removal on large forgings, rough-machined castings, and bar stock with significant diameter reduction requirements.

Geometry Characteristics

HS extends HM’s depth capability to 9 mm through a modified chip groove profile that maintains chip control at extreme depths. The wider groove accommodates the larger chip cross-section generated at deep cuts, while the raised backwall provides consistent chip breaking even when the full 9 mm depth is engaged.

The key difference from HM is the chip groove width and backwall position. HS places the backwall further from the cutting edge, giving thick chips from deep cuts enough room to curl before contacting the obstruction. This prevents chip jamming that would otherwise cause insert breakage or surface damage at extreme depths.

When to Use HS

Reserve HS for dedicated roughing operations where DOC regularly exceeds 5 mm. Common applications include first-pass roughing of forging stock, large shaft turning from bar, and any operation where removing maximum material per pass reduces total cycle time. HS is not suitable for finishing or medium operations due to the high minimum DOC requirement (below 2 mm, chip control deteriorates).

MM – Medium Machining (Universal Default)

Specifications

Feed range: 0.15-0.35 mm/rev. Depth of cut: 0.8-4.0 mm. Target: General-purpose turning covering the majority of production operations from medium roughing through semi-finishing.

Geometry Characteristics

MM represents Korloy’s universal chipbreaker geometry with the widest usable application window. It employs a moderate land width (0.08-0.12 mm) with a balanced chip groove that produces acceptable chip control across a broad range of feeds and depths without excelling at any extreme.

The rake angle is neutral to slightly positive, providing a good compromise between edge strength and cutting force. The chip groove depth is moderate, generating enough curl for breaking at medium feeds while remaining functional at the lower end of the feed range where aggressive grooves would produce over-curled, compressed chips.

When to Use MM

MM is the correct starting point when you are unsure of exact cutting conditions, when the operation varies between roughing and semi-finishing within the same program, or for general job-shop work where one insert must handle multiple operations. It pairs well with all PC-series grades and covers approximately 60% of typical turning applications.

HMP – Heavy Machining Positive

Specifications

Feed range: 0.20-0.45 mm/rev. Depth of cut: 1.5-6.0 mm. Target: Heavy roughing with reduced cutting forces, particularly beneficial for stainless steel, low-rigidity setups, and power-limited machines.

Geometry Characteristics

HMP combines the depth capability of HM with positive rake geometry, achieving 12-18% lower spindle load compared to HM at equivalent cutting parameters. This is accomplished through a more aggressive positive rake angle (8-12 degrees) combined with a reinforced edge treatment that maintains adequate strength despite the positive geometry.

The chip groove on HMP is designed to handle the thinner chips produced by positive rake cutting. Since positive geometry reduces chip thickness for a given feed rate, the groove dimensions are adjusted to maintain the curl radius needed for reliable breaking.

When to Use HMP

HMP is the preferred choice over HM in three scenarios: machining stainless steels where force reduction minimizes work hardening; turning on machines with limited spindle power where HM would require reduced parameters; and long-overhang setups (L:D > 3:1) where lower cutting forces reduce chatter tendency. The 12-18% force reduction translates directly to reduced deflection and improved surface quality in these challenging setups.

NM – Negative Medium / Light Finishing

Specifications

Feed range: 0.08-0.20 mm/rev. Depth of cut: 0.3-2.0 mm. Target: Finishing and light semi-finishing where surface quality and dimensional accuracy are primary concerns.

Geometry Characteristics

NM features the sharpest edge preparation in the lineup with a narrow land (0.03-0.06 mm) and a shallow, precisely formed chip groove. The low cutting forces generated by the sharp geometry produce minimal workpiece deflection, making NM essential for achieving tight tolerances on slender shafts and thin-walled components.

The chip groove profile in NM is optimized for the thin chips produced at light feeds. The shallow groove and close backwall ensure that even the thin chips generated at 0.08 mm/rev still make contact with the breaking geometry rather than flowing freely as long ribbons.

When to Use NM

NM is required for any operation where surface finish or dimensional tolerance is the primary acceptance criterion. It is also the correct choice for finishing hardened steels (35-45 HRC) where light cuts and sharp edges minimize white layer formation and residual stress concerns.

Chip Morphology Reference Table

Practical Selection Examples

Example 1: Roughing a 4140 Steel Shaft from Forging Stock

Workpiece: AISI 4140, 250mm diameter forging, rough-turned to 220mm. Conditions: DOC = 5mm per pass, feed = 0.35 mm/rev, speed = 220 m/min with PC5300 grade.

Decision: DOC of 5mm eliminates NM and MM (max 2mm and 4mm respectively). Both HM (max 7mm) and HS (max 9mm) qualify. Since 5mm is well within HM’s range and we do not need HS’s extended 9mm capability, HM is the correct choice. HS would work but offers no advantage here and may produce less consistent chip control at the 5mm depth since it is optimized for the 6-9mm range.

Example 2: Semi-Finishing 316L Stainless Flanges

Workpiece: AISI 316L stainless, OD turning with DOC = 2.0mm, feed = 0.22 mm/rev, speed = 180 m/min with PC9530 grade.

Decision: The moderate DOC and feed place this operation in the overlap between MM and HMP. For stainless steel, HMP is preferred over MM because the 12-18% force reduction minimizes work hardening of the machined surface and reduces the tendency for built-up edge formation. The positive geometry of HMP complements PC9530’s anti-adhesion coating to deliver the best possible surface quality on this difficult material.

Selection Summary

Conclusion

Korloy’s chipbreaker coding system creates a logical progression from maximum material removal (HS) through general-purpose versatility (MM) to precision finishing (NM), with HMP providing a force-reduced alternative for challenging materials and setups. Selecting the correct chipbreaker based on actual feed rate and depth of cut, rather than defaulting to MM for everything, typically improves chip control by two ISO chip form grades and extends edge life by 20-40% through proper load distribution across the cutting edge.

Contact Hooguu for chipbreaker samples and application engineering support to optimize your Korloy insert selection.