CNMG vs WNMG vs DNMG vs TNMG: choosing a turning insert shape

The four inserts side by side

All four are negative (0° clearance), double-sided inserts with a cylindrical hole and a chipbreaker on both faces. The sizes in the table all have a 12.7 mm (½ in) inscribed circle. That does not make them the same size: the edge length changes with the shape, and DNMG1506 is 6.35 mm thick where the others are 4.76 mm.

The smaller TNMG1604.. size has a 9.525 mm (⅜ in) inscribed circle and a 16.5 mm edge.

Nose angle: strength against access

The nose angle is the angle of the corner that cuts. Cutting-tool makers give the same rule: use the largest nose angle the part allows. A larger angle gives a stronger edge and allows higher feeds, but it needs more machine power and has a higher tendency to vibrate. A smaller angle reaches into profiles and recesses, with lower cutting forces and less vibration, but the corner is weaker.

• 80° (CNMG, WNMG): strong, the usual first choice for turning and facing.
• 60° (TNMG): a compromise between strength and access, with six edges.
• 55° (DNMG): reaches into profiles and tapers; take lighter cuts.

CNMG vs WNMG

Both have an 80° cutting corner. A WNMG trigon has three 80° corners on each face, six edges in all; a CNMG has two on each face, four in all. So at equal insert prices, and with all corners usable, WNMG has a lower purchase cost per cutting corner. The real cost also depends on tool life and how fast each insert cuts.

For the same 12.7 mm inscribed circle, though, the CNMG edge is about 12.9 mm long and the WNMG edge about 8.7 mm, so CNMG can support deeper cuts; check the recommended depth range of the insert and chipbreaker. Choose CNMG for heavy roughing and large depths of cut; choose WNMG for general turning and facing at moderate depths, where the extra corners pay off.

CNMG sizes we make: CNMG090304, CNMG090308, CNMG090408, CNMG120402, CNMG120404, CNMG120404L, CNMG120404R, CNMG120408 and 17 more.

WNMG sizes we make: WNMG060402, WNMG060404, WNMG060406, WNMG060408, WNMG060412, WNMG06T302, WNMG06T304, WNMG06T308 and 11 more.

CNMG vs DNMG

DNMG has a 55° corner. It turns profiles, tapers and recesses that an 80° corner can’t reach, and it is often used for copying work. The narrower corner is weaker and more sensitive to heavy feeds and interrupted cuts, so use CNMG wherever the part allows it and DNMG where the contour needs its clearance.

DNMG sizes we make: DNMG110404, DNMG110408, DNMG110412, DNMG150404, DNMG150408, DNMG150412, DNMG150604, DNMG150604L and 6 more.

Where TNMG fits

TNMG has six corners like WNMG, with a longer cutting edge for its size but a 60° corner instead of 80°. It is an economical choice for general turning and facing. Where corner strength matters more than the number of corners, CNMG or WNMG is the stronger choice.

TNMG sizes we make: TNMG120412, TNMG160402, TNMG160404, TNMG160404L, TNMG160404R, TNMG160408, TNMG160408L, TNMG160408R and 7 more.

Holders

Each shape needs a holder made for it; a WNMG insert does not fit a CNMG pocket. Common external holders have an entering angle (κr) of 95° for CNMG and WNMG (turning and facing with one tool), 93° for DNMG (profiling) and 91° or 93° for TNMG; other styles exist for each shape. Confirm the insert size and clamping system with your holder before ordering.

How to choose, in order

1. Does the contour need the clearance of a narrower corner, to reach into a profile, taper or recess? Then DNMG (55°); deeper profiles may need a smaller corner still.
2. Otherwise use the largest nose angle the part allows: an 80° CNMG or WNMG.
3. Large depths of cut: CNMG, for its longer edge. General turning at moderate depths: WNMG, for six corners.
4. Then choose the size so that the edge is long enough for your depth of cut, a nose radius that suits the depth of cut (as a starting rule, no larger than it, especially where vibration is a concern), and a chipbreaker and grade for your material (see the ISO material groups).

Not sure what a code means? The insert designation decoder reads any ISO insert code position by position.

Questions

What does NMG mean in CNMG, WNMG, DNMG and TNMG?

N is a 0° clearance angle (a negative insert), M the tolerance class and G a cylindrical hole with a chipbreaker on both faces. The first letter is the shape: C 80° rhombic, W 80° trigon, D 55° rhombic, T 60° triangle.

Is CNMG or WNMG better for roughing?

For the same inscribed circle, CNMG has more nominal edge length than WNMG, which can support deeper cuts; check the recommended depth range of the specific insert. WNMG has six cutting corners instead of four, which can lower the purchase cost per corner on general turning and facing; the real cost also depends on price, tool life and productivity.

Can I put a WNMG insert in a CNMG holder?

No. Each shape needs a holder with a pocket for that shape. Holders and boring bars are made for one insert shape and size.

When should I use DNMG instead of CNMG?

Use DNMG when the contour needs the extra clearance of a 55° corner, for example in profiles, recesses or tapers. Its corner is weaker than an 80° corner, so CNMG is the safer choice for straight turning, facing and heavier roughing.