Machining a hardened ring gear

Incorrect speeds and feeds are a surefire way to make terrible noises, break tools and scrap parts. Our initial attempts to machine a hardened ring gear made noises that would make any machinist shudder. Through experimentation, we optimized reliable recipes that result in an excellent surface finish and provide good tool life.

These ProvenCut recipes were performed on a Tormach 1100, a 499-kg (1,100-lb.), 1.1-kW (1.5-hp) CNC mill. It has similar capabilities as a Bridgeport. Tormach machines target the “prosumer” market and often are found in garage shops and R&D departments.

Although cutting tools designed specifically for hard milling are available, we chose a standard four-flute carbide endmill that many machinists already have on hand. Our testing focused on avoiding cutting tool vibration and ensuring that excessive heat was not created. We pushed the tool and machine to achieve an aggressive but sustainable roughing recipe and concentrated on the surface finish of the workpiece for the finishing recipe. Machining 8620 alloy steel hardened to 55 HRC can leave an outstanding surface finish with luster even when cut on a small CNC machine.