ISO Turning Inserts

Work down in this order. Shape is fixed by the holder you already own, so start there unless you are buying both. Then size and nose radius, from your depth of cut and the finish you need. Then grade, from the material you are cutting — that is the ISO P, M, K or N choice further up this page. Then chipbreaker, from whether you are roughing or finishing. Get the last two wrong and the insert will still cut, it just will not last.

Seven positions, left to right: shape, clearance angle, tolerance class, hole and chipbreaker form, inscribed circle size, thickness, nose radius. So CNMG120408 is an 80° rhombic, 0° clearance, M tolerance, hole with chipbreaker, 12mm IC, 4.76mm thick, 0.8mm nose radius. The table above breaks each position down.

12 is the inscribed circle in millimetres — the diameter of the largest circle that fits inside the insert — and 04 is the thickness, 4.76mm. Both are rounded, so they are not exact dimensions. The IC has to match your holder pocket; the thickness is about how heavy a cut it will take.

An ISO M grade — tougher substrate, sharper edge, and a geometry that keeps the chip moving. Stainless work-hardens the moment you let the tool rub, so the failure mode is usually a dull edge causing a hard skin rather than the insert wearing out.

Position two of the code. N is 0° clearance, double-sided, so you get twice the edges but it needs more power and rigidity. C is 7° positive, single-sided, and cuts more freely — better on thin wall, slender parts and smaller machines. They are not interchangeable in a holder.

Small for finishing and anything slender, large for roughing. The working rule is to keep feed below roughly half the nose radius, so a 0.4mm radius tops out around 0.2mm per rev. A big radius is stronger and lets you push depth, but it also pushes the part away.

They are Palbit's grade designations, and they map to material group. PHG and PHG140 are steel grades, PH5705 and PH5320 are cast iron, PHH910 and PHH920 are stainless and exotics, PH0910 is aluminium. If you know the grade you can work backwards to the material it was designed for.

It will cut, but it will not last. Cast iron wears an edge abrasively where steel wears it thermally, so the coatings and substrates are built differently. A cast iron grade on cast iron will often triple the edge life for the same money.

The moulded geometry on the insert face that curls and snaps the chip. It matters enormously — the wrong one gives you long stringy swarf that wraps the part, or forces so high they chip the edge. Finishing chipbreakers work at light depth and feed, roughing ones need depth to function at all.

The holder's designation encodes the insert it takes, and the shape and clearance letters have to match. A CNMG insert needs a holder with C in the insert-shape position and negative geometry. If you have the holder, tell us the code and we will tell you the insert.

No — the range is 2,452 lines and we hold the common combinations. If a size and grade pairing is not showing, it is usually available to order in a day or two, so ring rather than assuming.