Indexable insert guide

A typical turning code such as CNMG 120408 is seven fields: shape, clearance, tolerance, hole and breaker, size, thickness, nose radius. Optional letters after that are edge condition and hand. A hyphenated tail is the manufacturer's chipbreaker or grade name — it is not standardised.

Milling and indexable-drill inserts use the same first four letters. Grooving and threading do not; those families are listed separately in the library.

• Uncoated carbide · to about 800 °C. Sharp and chemically quiet. Still used on titanium, HRSA and some aluminium where a coating would smear or react. Wears faster than coated grades on steel.
• CVD-coated carbide · to about 1000 °C. Thick chemical-vapour coatings (often gold TiN over alumina). First choice for wear resistance in general steel and iron turning. The coating is applied hot, so the edge is a little less sharp than PVD.
• PVD-coated carbide · to about 1000 °C. Thinner physical-vapour coatings keep a sharp edge. Preferred for stainless, titanium, grooving, threading, milling and finishing. Dark TiAlN and copper AlTiSiN are common shop colours — colour is a hint, not a spec.
• Cermet · to about 1000 °C. Ceramic-metal. Excellent finish and wear resistance on stable steel finishing. Poor interrupted-cut toughness. Do not use as a roughing substitute for carbide.
• Ceramic · to about 1200 °C. Very hard, high speed, dry or with carefully applied coolant. Cast iron, hardened steel and some nickel alloys. Needs a rigid machine and a T-land. Thermal shock will crack it.
• CBN (cubic boron nitride) · to about 2000 °C. Hard-turning and cast-iron finishing. Solid or tipped. Do not run CBN in carbon steel at conventional speeds — it wears chemically. SUMIBORON-style solid CBN is a turning special, not a general CNMG replacement.
• PCD (diamond) · to about 700 °C. Extreme wear resistance on aluminium, composites and non-ferrous. Carbon steel dissolves diamond; never use PCD on ferrous alloys.

Shop colour is a hint, not a specification

• Gold / brass. Often TiN. General-purpose wear coat. Colour alone does not name the grade.
• Black / anthracite. Often TiAlN or AlTiN. Harder materials and dry milling.
• Copper. Often AlTiSiN-type. Hard steel and cast iron milling.
• Bright ground / silver. Uncoated or polished. Aluminium, copper, plastics, sharp stainless edges.

• P — Steel. Carbon and alloy steels, free-cutting steels.
• M — Stainless. Austenitic and duplex stainless, work-hardening alloys.
• K — Cast iron. Grey, nodular and malleable irons.
• N — Non-ferrous. Aluminium, copper alloys, plastics.
• S — Heat-resistant. Titanium, nickel alloys, HRSA.
• H — Hardened. Hardened steel, typically above 45 HRC.

ISO 1832 stops at the hyphen. The tail is a catalogue name. The same letters are a different groove from another maker.

• -PF — Often a finishing chipbreaker in that maker's catalogue. The same letters mean a different groove from another maker.
• -PM — Often a medium / general-purpose chipbreaker in that maker's catalogue. Confirm the geometry in their chart.
• -PR — Often a roughing chipbreaker in that maker's catalogue. The same letters mean a different groove from another maker.
• -MF — Often a stainless finishing chipbreaker in that maker's catalogue. Read it in their chart — it is not ISO 1832.
• -MM — Often a stainless medium chipbreaker in that maker's catalogue. Confirm the geometry in their chart.
• -MR — Often a stainless roughing chipbreaker in that maker's catalogue. Confirm the geometry in their chart.
• -23 / -M3 — A numbered chipbreaker or grade (for example -23 or -M3). It is a catalogue name, not part of ISO 1832.

Maker chipbreaker or grade. Read it in that maker's catalogue — it is not part of ISO 1832.

• Pick the largest point angle the job will allow — strength first, then reach.
• Keep the nose radius no larger than the depth of cut, or the tool rubs and chatters.
• Size the insert from the largest depth of cut and the holder setting angle, then go one size up if the cut is interrupted.
• Negative (0°) inserts for rigid roughing; positive (7° or 11°) for finishing, boring and slender parts.
• CVD when wear life on steel or iron matters; PVD when you need a sharp edge or the material smears.
• A large setting angle (approaching 90°) pushes force into the chuck and lets you square a shoulder; a small angle thins the chip and raises radial force.

For spindle speed and feed, use the speeds and feeds calculator.

The insert must match the flank angle and form. A 60° metric full-profile insert will not cut a correct Whitworth or Acme thread.

• Metric ISO (60°) — Most drawings. Full-profile inserts are stamped 1.0ISO, 1.5ISO, …
• UN / UNF / UNC (60°) — Same 60° flank, different pitch series. Do not mix with metric full-profile.
• Whitworth / BSW (55°) — 55° and a rounded crest and root. Needs a 55° insert.
• BSP / G (55°) — Pipe thread, 55°. Parallel (G) and taper (R) are different inserts.
• NPT (60°) — Taper pipe, 60°. Not interchangeable with metric ISO.
• Acme (29°) — 29° stub form for leadscrews. Dedicated insert.
• Trapezoidal (Tr) (30°) — Metric power screw, 30°. Dedicated insert.
• API (60°) — Oil-country forms. Match the exact API designation.