HRC

Deep Hole Drilling Hardened Steels (HRC 40+): Parameters and Tooling That Work Hardened steels are a different animal. I learned this the hard way — watching a brand-new carbide gun drill snap on the third hole because I treated the material like it was standard 4140. After a lot of scrap parts, broken tools, and late-night spindle-side debugging, I landed on a set of parameters and tooling choices that turn hardened steel deep-hole drilling from a gamble into a repeatable process. Here is what actually works on the floor. ...