When hard turning replaces grinding
The economic case rests on cycle time and process consolidation rather than insert price. A hard-turning operation removes the grinding machine, its wheel dressing, its coolant system and its separate set-up, and frequently completes one of those operations in a single pass on a lathe.
It is strongest where batch sizes are large enough to develop and verify the process, where grinding wheels cannot reach a profile in one set-up, and where part geometry makes fixturing for grinding difficult or expensive.
Where grinding still wins
Hard turning does not match grinding on the tightest roundness and surface-finish tolerance bands, and it produces a surface with different residual stress characteristics. For fatigue-critical parts where the loading direction matters, a ground surface may still be specified. Bearing races and certain transmission components often fall into this category.
Grade and geometry direction
Continuous hard turning favours a high-CBN-content grade at the higher end of the speed range for maximum edge life and finish consistency. Interrupted profiles require a lower-CBN-content grade with ceramic binder, a stronger edge (round or square, negative rake) and reduced speed. The edge preparation — including a chamfer or hone — matters as much as the grade for surviving impact.
Recommended cutting conditions by grade (Koves catalogue)
Official PCBN conditions for hardened steel turning, quoted from the Koves catalogue. Speed values are reproduced exactly as printed (three-part values such as 110–180–300).
If your operation is not listed, send us the workpiece drawing and hardness — we will specify the grade and geometry.
| Application | Grade | Vc (m/min) | f (mm/rev) | ap (mm) |
|---|---|---|---|---|
| Continuous cutting | KBN5010 | 110–180–300 | 0.03–0.10–0.20 | 0.03–0.20–0.35 |
| General cutting | KBN6020 | 80–160–200 | 0.03–0.10–0.20 | 0.03–0.20–0.35 |
| Interrupted cutting | KBN7030 | 60–100–180 | 0.03–0.10–0.20 | 0.03–0.20–0.35 |
Parameter guidance
Depth of cut in hard turning is normally small, because the objective is a finishing operation rather than bulk removal. The practical levers are therefore cutting speed and feed, and speed should be set from the grade and operation type first.
| Operation | Hardness | Vc (m/min) | ap (mm) | f (mm/rev) |
|---|---|---|---|---|
| Continuous finishing | HRC 55–65 | 120–250 | 0.05–0.30 | 0.05–0.15 |
| Continuous light roughing | HRC 45–58 | 100–200 | 0.2–0.8 | 0.10–0.30 |
| Interrupted finishing | HRC 50–62 | 60–150 | 0.05–0.40 | 0.05–0.15 |
| Interrupted roughing | HRC 45–55 | 60–120 | 0.2–1.0 | 0.08–0.25 |
Related case studies
Field-proven results behind the grade recommendations on this page:
- KBCN5010 (coated) — 16MnCr5 case-hardening steel, continuous turning (od): 890 pcs — about 30% longer life
- KBCN5010 (coated) — Hardened steel, continuous turning (od): 1,820 pcs
- KBN6020 — TL4227, grooving: 1,102 pcs — more than 2× the reference
- KBN7030 — S45C medium-carbon steel (gear), face turning: 70 vs 45 pcs
- KBN7030 — SCr415H case-hardening steel (gear), bore / internal turning: 170 vs 110 pcs
- KBN9020 — D2 cold-work tool steel, continuous turning (od): 2,229 pcs on two edges
All 36 machining case studies →
Frequently asked questions
At what hardness does hard turning become worthwhile?
Can PCBN handle interrupted cuts in hardened steel?
Send us your workpiece material, hardness and machine parameters. Our engineers will recommend the right grade and cutting data.