Hard turning has transformed the machining of hardened steels, enabling manufacturers to produce precise CNC turning components without the need for secondary grinding. When processing materials like case-hardened or through-hardened alloy steels at HRC 58–62, advanced CBN (cubic boron nitride) tooling on rigid CNC lathes delivers tight tolerances, excellent surface finish, and compelling cost efficiency. This article explores the critical process parameters, achievable quality levels, and economic benefits of producing CNC turning components through hard turning.

Critical CBN Tool Parameters for Hard Turning

Success in hard turning CNC turning components starts with the right CBN insert selection and cutting data. The following parameters are recommended for continuous and lightly interrupted cuts in 58–62 HRC steel:

Using a low CBN content grade with a ceramic binder and a wiper insert geometry (learn more from Sandvik Coromant’s hard part turning guide) helps balance toughness and wear resistance. Negative rake angles and rigid clamping are essential to suppress vibration and achieve consistent CNC turning components quality.

Process Capability: IT6 and Surface Finish

Modern CNC turning centers easily hold IT6 dimensional tolerance on diameters and lengths for CNC turning components when the machine is thermally stable and equipped with linear scales. At Start Precision, our precision equipment list includes rigid multi-axis lathes such as the Germany DMG CTX beta 800 and Japan TAKZSAWA NEX-108, which provide the structural stiffness and high-pressure coolant capability essential for hard turning.

Surface finishes typically reach Ra 0.2–0.4 µm, matching or exceeding ground surfaces in many bearing and automotive applications. With tight process control, 80% of our hard-turned CNC turning components meet an IT6 requirement without a grinding allowance.

Cost and Efficiency: Hard Turning vs. Grinding

A systematic cost comparison reveals why many production shops are switching to hard turning for CNC turning components:

By consolidating roughing and finishing into one operation, hard turning dramatically reduces throughput time and eliminates the capital cost of additional grinders. When machining batches of highly accurate CNC turning components, total per-part cost often drops by 30–50%.

Real-World Application: Hardened Steel Shaft

A recent project highlights the advantage. We produced a batch of 2,000 case-hardened 20MnCr5 shafts hardened to HRC 60, requiring an inner bore tolerance of IT6 and a surface finish better than Ra 0.4 µm. Previously, the parts required cylindrical grinding after turning. Using DMG CTX beta 800 with a wiper CBN insert, we hard-turned the complete bore in one pass at Vc=160 m/min, f=0.12 mm/rev, ap=0.3 mm. The CNC turning components met the IT6 requirement across the entire batch, Ra averaged 0.3 µm, and cycle time fell from 55 seconds to 18 seconds per part. Part cost was reduced by 42%, and the grinder was freed for other critical operations.

Quality Assurance and Certification

All our CNC turning components are manufactured in an ISO 9001:2015 certified facility that includes in-process measurement, CMM inspection, and SPC tracking. This ensures that every hard-turned part complies with the demanded IT6 tolerance and surface integrity criteria.

Our quality system is certified to ISO 9001:2015 for precision CNC turned parts.

Whether you need prototype quantities or high-volume delivery of hardened steel CNC turning components, hard turning provides a lean, accurate, and economical route. Contact us today to discuss your manufacturing needs.