CNC / machinist calculator
Turning Insert Designation Decoder (ISO 1832 / ANSI)
A turning insert code like CNMG120408 or its ANSI form CNMG432 packs seven facts into a few characters: the insert shape and angle, the clearance, the tolerance class, the hole and chipbreaker type, and the size, thickness and nose radius. Type a designation and this decoder spells all of it out, and translates between the ISO metric block and the ANSI inch block so you can read either one a supplier throws at you.
Enter a designation, e.g. CNMG120408 or CNMG432
| Position | Code | Meaning |
|---|
How it works
The first four characters are always letters. The first is the shape, which also fixes the included angle: C is an 80 degree diamond, D a 55 degree diamond, V a 35 degree diamond, S a square, T a triangle, W an 80 degree trigon, and R a round. The second is the clearance angle, from N at zero degrees for a double-sided negative insert up through B at five, C at seven and P at eleven. The third is the tolerance class, ground or pressed, and the fourth is the type, which describes the fixing hole and whether there is a chipbreaker on one or both faces.
The number block is where ISO and ANSI differ. ANSI uses inch fractions: the size digit is the inscribed circle in eighths of an inch, the thickness in sixteenths, and the nose radius in sixty-fourths, so the 4, 3 and 2 of a 432 are a half-inch circle, three-sixteenths thick, with a one thirty-second radius. ISO uses metric: the size is a cutting-edge-length symbol that depends on the shape, the thickness is a coded millimetre value, and the last two digits are the nose radius in tenths of a millimetre, so 08 is 0.8 mm. The decoder shows both.
Worked example
CNMG120408 is an 80 degree diamond (C), zero degrees clearance (N), medium tolerance (M), with a cylindrical hole and chipbreaker both faces (G), a 1/2 in inscribed circle, 4.76 mm thick, and a 0.8 mm nose radius. Its ANSI twin is CNMG432.
Frequently asked questions
What does CNMG mean on an insert?
C is an 80 degree diamond shape, N is zero degrees clearance so it is a double-sided negative insert, M is a medium pressed tolerance, and G is a cylindrical hole with a chipbreaker on both faces. The numbers after give the size, thickness and nose radius.
How does the ANSI code map to the ISO code?
The four letters are the same. The ANSI numbers are inch fractions and the ISO numbers are metric. For example ANSI 432 is a half-inch inscribed circle, three-sixteenths thick, with a one thirty-second radius, which is ISO 120408: size 12, thickness 04, radius 08 which is 0.8 mm.
What does the clearance letter mean?
It is the relief angle ground into the insert flank. N is zero degrees, which is a double-sided negative insert used for roughing; positive clearances like C at seven degrees or P at eleven are single-sided and cut with less force, better for finishing and lighter machines.
What is the nose radius and where is it in the code?
The nose radius is the last part of the number block. In ISO it is the last two digits in tenths of a millimetre, so 08 is 0.8 mm; in ANSI it is the last digit in sixty-fourths of an inch. A larger radius is stronger and gives a better finish, a smaller one is needed for sharp corners and less cutting force.
Does it decode every insert shape and code?
It decodes the common turning shapes and all seven positions of the standard designation. A few rare shape angles and the exact numeric tolerance values are defined by the ISO 1832 standard and manufacturer tables and are noted rather than asserted; check the maker's catalogue for those.
Related calculators
Coverage
Implements ISO 1832 / ANSI B212.4 (indexable turning inserts): All seven designation positions decoded, Common shapes C D V S T W R, ISO metric and ANSI inch number blocks, Size, thickness and nose radius in both inch and mm. Deliberately not offered yet:
- Included angles for the rare shapes A B E K L M H O P (K is the niche KNUX parallelogram; P pentagon is a milling shape, not turning) - single-sourced; not asserted as certified without the ISO 1832 text or Machinery's Handbook
- Numeric tolerance-class values (m, s, d) for classes M and U - these vary with insert size and are tabulated in ISO 1832 and manufacturer catalogues, not derived here
Sources
- ISO turning inserts nomenclature (Machining Doctor)
- Turning insert nomenclature ANSI/ISO (Ingersoll Cutting Tools)
- Indexable insert guide, ISO 1832 codes (AIMS Industrial)
Every formula on this page is shown and sourced. See how we verify.
These calculators are for planning and as a starting point. Recommended speeds and feeds are published starting values that vary with your specific tool, coating, machine rigidity, workholding and coolant. Always start conservative, listen to the cut, and follow your tool maker data sheet.