Have you ever tried a button cutter for milling?
If so, you’ll know that these versatile tools can really do a good job for you. They’re commonly used for pocketing, die/mold roughing, face milling, slotting, step milling, and even helical interpolation of holes.
There’s a lot to recommend round inserts as they have a number of properties that contribute to their success. If you’ve used one turning, you know that their large radius can yield some very nice surface finishes. They can leave a good finish when milling too, but they have a number of other advantages.
Their round shape makes them particularly strong as they have no weak corners that can chip. If you do wear or chip one, they can be rotated to expose a fresh edge.
They’re advantageous for lighter machines too. When operating at heavier depths of cut, they create cutting forces that are more radial. But, by taking a lighter depth of cut, they transition to behave more like high-feed machining tools. This means most of the cutting forces are directed straight up the spindle, which is the strongest rigidity on any machine. That’s one reason plunge milling is so advantageous on light machines. Button cutters provide an alternative.
It seems that for whatever reason, the physics of cutting favors circles. HSM toolpaths do better than conventional paths by adopting loops rather than sharp corners. And button cutters do well because corners on inserts are a weak point that can chip or break off. You can load up a button cutter pretty hard and they’ll hang in there. If you do manage to chip one, just rotate the insert until the chipped portion is not being used and keep going.