Hard milling is an offshoot of high speed machining techniques. The goal is to create an as-machined surface that drastically reduces the need for subsequent processing. For the cutting tool to achieve an effective chip load, feed rates and spindle speeds must be much higher than those normally applied in traditional machining. The high feed rates also make it possible to complete a much larger number of passes across the workpiece more quickly than with traditional methods.
Hard milling takes the concept of high speed machining one step further. The combination of light cuts at high feed rates and spindle speeds makes it possible to remove steel in the hardened state efficiently when all of the proper conditions are met. Likewise, closely spaced stepovers with small-diameter, radiused tools leave a surface that approaches the fineness of one that has been stoned or polished by hand. Because steel is already hardened, subsequent heat treating, stress relieving or grinding steps are unnecessary. More importantly, the process also replaces many costly steps with EDM.