Insert shape and what it decides
The included angle of the point sets the trade-off. Sharper points cut freely and reach into profiles but have less material behind the edge, so they fail sooner under load.
Higher-point-count inserts cost more per edge but are stronger, which usually wins on roughing and interrupted cuts.
| Shape | Point angle | Typical use | Trade-off |
|---|---|---|---|
| C (CNMG/CCMT) | 80 degrees | General turning, roughing, interrupted cuts | Strong edge, but limited profile access |
| S (SNMG/SCMT) | 90 degrees | Square shoulders, facing, heavy turning | Very strong, cannot profile |
| D (DNMG/DCMT) | 55 degrees | Profiling, medium turning, copy turning | Good compromise of access and strength |
| V (VNMG/VCMT) | 35 degrees | Finishing, tight profiles, slender parts | Sharpest and weakest; needs light cuts |
| T (TNMG/TCMT) | 60 degrees | Light turning, small diameters, boring | Versatile, less rigid than C or S |
| W (WNMG/WCMT) | 80 degrees, trigon | Roughing with a strong point | Six usable edges, strong, but special holder geometry |
Grades: the ISO colour system
Insert grades are classified by the ISO P, M, K, N, S and H groups, which describe the workpiece material rather than the insert itself. The colour code is a convention rather than a law, but most manufacturers follow it, so it is worth knowing.
Within a group, the grade number trades toughness against wear resistance. A lower number in the range is harder and resists wear; a higher number is tougher and resists chipping.
| Group | Material | Colour code | Coating direction |
|---|---|---|---|
| P | Steel, cast steel, ferritic and martensitic stainless | Blue | CVD TiCN/Al2O3 for wear resistance |
| M | Austenitic stainless, duplex, manganese steel | Yellow | PVD TiAlN; sharper edge to limit work hardening |
| K | Grey and nodular cast iron | Red | CVD or TiCN; toughness against interrupted cuts |
| N | Aluminium, copper, brass, plastics | Green | Polished and uncoated or DLC; sharp, non-sticking |
| S | Titanium, nickel and cobalt alloys | Brown | PVD AlTiN; hot hardness and edge integrity |
| H | Hardened steel, chilled cast iron | Grey or black | Ceramic, CBN or PVD-coated carbide |
Chip breakers do the real work
A grade tells you how the insert survives; the chip breaker tells you whether the operation works at all. A chip that curls and breaks is a chip that leaves the cutting zone. A chip that strings wraps around the tool, scratches the finished surface and eventually stops the machine.
Breakers are matched to depth of cut and feed, not to material alone. A finishing breaker run at a roughing feed will not break the chip, and a roughing breaker run at a light feed will rub instead of cutting. Tell us your depth of cut and feed range, and we will match the breaker to it.
CVD and PVD coatings
CVD coatings are applied hot and are thicker, which gives excellent wear resistance in continuous cuts on steel and cast iron. They are also slightly thermally loaded, which is why they suit turning better than milling.
PVD coatings are applied at lower temperature and are thinner with a sharper edge, which suits stainless, titanium and interrupted cuts, and is the usual choice for milling and for threading.
Frequently asked questions
Which insert shape should I start with?
CNMG covers general turning and roughing and is the usual starting point. Move to DNMG or VNMG when you need to profile or finish, to WNMG for heavy roughing where edge strength dominates, and to TNMG for small diameters and boring.
How do I know which grade to choose?
Start from the material group: P for steel, M for stainless, K for cast iron, N for aluminium, S for titanium and nickel alloys, H for hardened steel. Then move within the group towards a harder grade for continuous cutting and a tougher grade for interrupted cuts.
What is the difference between CVD and PVD coatings?
CVD gives a thicker, more wear-resistant coating and suits continuous turning of steel and cast iron. PVD gives a thinner coating with a sharper edge, which suits stainless, titanium, interrupted cuts and most milling and threading applications.
Do you supply the tool holders for these inserts?
Yes. Inserts and the holders that locate them are supplied together, because insert pocket wear in the holder is a common cause of poor repeatability and unexplained insert breakage.
Can you supply inserts to match another brand's grade?
We can match the shape, tolerance class and chip breaker, and propose an equivalent grade for your material. Send the insert or its designation and the operation, and we will confirm the substitution and its limits.