There are an absolute ton of different insert geometries. I'd categorize them as standard and proprietary. The standard inserts are available everywhere and are easy to find matching holders. Every manufacturer also has proprietary inserts. These are usually custom made to fit a specific tool or family of tools. Often they are targeted at a higher performance market who is willing to buy into the family of tools and supporting hardware.
I'd recommend sticking to the common shapes and sizes. Here is an example list which is far from inclusive.
- CNMG (Most common insert, general purpose, negative rake, high cutting forces, my 12x36 can barely handle these, CNMG432 is most common)
- CCMT (Positive rake general purpose insert, my go-to, CCMT32.50 is my favorite)
- TCMT (Triangle insert, often used on boring bars)
- DCMT (medium diamond insert, weaker than CCMT, stronger than VCMT. DCMT21.51 fits some of my boring bars)
- VCMT (sharp diamond insert, weak, but low cutting forces and excellent accessibility, ideal for fine finishing, VCMT110304 is my go to)
- SCMT (square insert, used for heavy turning or chamfers)
There are metric and imperial designations. For example CCMT31.51 and CCMT090304 are the same insert. The first is the imperial designation (used by Shars for example) and the second is the metric designation you'll see on AliExpress.
Next are different edge conditions and rake angles. xxMT is common for general purpose positive rake inserts (e.g. CCMT32.50). xxGX or xxGT are uncoated, high polish, sharp ground edge inserts great for plastic or non-ferrous metals (e.g. CCGT090304).
Finally, the corner radius is very important. In the imperial designation, the "31.5" is the insert size while the "0" is the corner radius (e.g. CCMT32.50 vs CCMT 32.52). "0" is a near sharp corner, "1" is a medium radius, and "2" is a heavy radius (manufacturers will provide the exact dimension. In the metric designation, the last 2 digits (e.g. "04" in CCMT090304) are the corner radius. "02" is near sharp, "04" is medium, and "08" is heavy. A heavy radius creates a stronger tool for roughing and ideally a better surface finish at high feed cutting, but tremendously higher cutting forces. A sharp edge will deflect the workpiece less, giving more accurate dimensions. The corner radius also determines the
minimum depth of cut you can take. I strongly recommend the near sharp corner for machines under a 12" swing. I rarely use the medium corner inserts and only for roughing.
The included angle of the insert also determines cutting forces. The lower the cutting forces, the more accurate your dimensions will be after the cut. That is why the VCMT (30 degree included angle) will finish more accurately than the CCMT (80 degree included angle) in most cases.
The xxGT edge condition also drastically reduces cutting forces, but is a weak edge. They are ideal for soft materials (and have excellent life), but also give good performance in alloy steel and especially stainless, although they have a much reduced insert life.
