Hard turning replaces grinding in many production applications. Done right, it delivers Ra 0.4 µm at 5-10× the productivity of grinding.
When Hard Turning Wins
- Surface roughness Ra 0.4-1.6 µm
- Geometric complexity (chamfers, profiles)
- One-piece flow vs grinding batch process
- Lower setup time
Tool Material: CBN Mandatory
| Hardness | Tool Material | Recommended Grade |
|---|---|---|
| 45-55 HRC | Coated carbide (limited) | Sandvik GC4315 + edge prep |
| 50-62 HRC | CBN (low content) | Sandvik CB7015 |
| 60-65 HRC | CBN (high content) | Sandvik CB7025, Iscar IB55 |
| 65-70 HRC | Ceramic SiAlON or solid CBN | Sandvik CC6090 |
Insert Geometry
- Negative rake — Mandatory for CBN strength
- T-land or honed edge — 25-45° T-land × 0.1mm wide
- Wiper geometry — Achieves Ra 0.4 µm at fn=0.20 mm/rev
Cutting Parameters
Hard turning runs FASTER than soft turning, with LIGHTER cuts:
- Vc: 150-250 m/min
- Feed: 0.10-0.20 mm/rev
- Depth: 0.10-0.30 mm
- Coolant: dry or MQL (NOT flood — thermal shock cracks CBN)
Cost Reality
CBN inserts cost $40-80 each (vs $5-15 carbide). Tool life 30-100 parts. Per-part insert cost typically $0.50-2.00, often less than grinding wheel cost.
Browse CBN inserts in our insert catalog.
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