Once steel is hardened past ~45 HRC, conventional milling and turning give way to hard turning (with CBN/ceramic tooling on a rigid machine), grinding, or EDM. The keys are extreme rigidity, thermal stability and the right tool grade — this is where a great machine separates from an average one.
Mold and die and bearing work live here. See hard turning, grinding and EDM for the routes, and tool steel for the material family.
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