CNC Milling for Alloy Steel 4140
4140 alloy steel mills cleanly in the annealed condition with predictable chip formation. In the pre-hardened condition (28-32 HRC), it requires carbide tooling with appropriate coatings.
Recommended Machining Parameters
| Parameter | Value |
|---|---|
| Achievable Tolerances | ±0.02 mm (±0.0008") |
| Surface Finish | Ra 0.8-3.2 μm |
| Cutting Speed | 80-150 m/min (SFM 260-500) |
| Feed Rate | 0.06-0.12 mm/tooth |
| Tooling Recommendations | Carbide end mills with TiAlN coating, 4 flutes. Use insert mills for roughing large volumes. |
Expert Machining Tips
1
Machine in annealed condition when possible
2
Use positive rake angles for better chip flow
3
Flood coolant recommended for heat dissipation
4
Through-hardened material requires reduced speeds
Common Parts Made
Toolholders
Shafts and spindles
Gear blanks
Coupling housings
Sprocket assemblies
Machining Challenges
- Higher hardness requires slower speeds
- Chip control important in deep pockets
- Pre-hardened condition accelerates tool wear