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Technical Guide
CNC Cutting Speed Guide
The right SFM makes the difference between a tool lasting 100 parts or 10.
Calculate RPM & Feed Instantly
Enter your material, tool diameter, and operation — get exact RPM, feed rate, and chip load recommendations.
SFM ↔ RPM Conversion
SFM → RPM
RPM = (SFM × 3.82) / Diameter
Example: Aluminum at 800 SFM with ½" endmill
RPM = (800 × 3.82) / 0.5 = 6,112 RPM
RPM → SFM
SFM = (RPM × Diameter) / 3.82
Example: Running 3,000 RPM on a ¾" endmill
SFM = (3,000 × 0.75) / 3.82 = 589 SFM
For detailed SFM/RPM conversion tables, see our SFM to RPM Conversion Guide.
Recommended Cutting Speed (SFM) by Material
These SFM values are for carbide tools (uncoated unless noted). HSS tools: use 30-50% of these values. Coated carbide (TiAlN, AlCrN): increase by 20-40%.
| Material | Roughing SFM | Finishing SFM | Calculator |
|---|---|---|---|
| Aluminum 6061-T6 | 600-1,000 | 800-1,500 | Calculate → |
| Aluminum 7075-T6 | 400-700 | 600-1,000 | Calculate → |
| Mild Steel (1018) | 350-500 | 400-600 | Calculate → |
| 4140 Steel (HRC 28-32) | 250-400 | 300-450 | Calculate → |
| Stainless 304 | 200-350 | 250-400 | Calculate → |
| Stainless 316 | 150-300 | 200-350 | Calculate → |
| Titanium Ti-6Al-4V | 100-200 | 150-250 | Calculate → |
| Inconel 718 | 60-120 | 80-150 | Calculate → |
| Cast Iron (Grade 40) | 250-400 | 300-500 | Calculate → |
| Copper / Brass | 300-600 | 400-800 | Calculate → |
When to Go Faster or Slower
✅ Increase SFM When:
- +Using coated carbide (TiAlN adds +20-40%)
- +High-pressure through-spindle coolant (1000+ PSI)
- +Rigid setup — short tool stick-out, solid workholding
- +Small WOC with high-efficiency toolpaths (e.g., HSM/dynamic milling)
- +Machine has high spindle power and good chip evacuation
❌ Decrease SFM When:
- −Using HSS or uncoated carbide tools
- −Long tool stick-out (>4×D) causing chatter
- −Thin walls or delicate features prone to deflection
- −Work-hardening materials (304 SS, Inconel) — never rub
- −Interrupted cuts (keyways, cross-holes, casting flash)
Tool Coating Impact on Cutting Speed
| Coating | SFM Increase | Best For | Max Temp (°F) |
|---|---|---|---|
| Uncoated Carbide | Baseline | Aluminum, non-ferrous | 1,200°F |
| TiN | +15-25% | General-purpose steel | 1,100°F |
| TiCN | +20-30% | Hard steels, stainless | 750°F |
| TiAlN | +30-50% | High-temp alloys, dry machining | 1,500°F |
| AlCrN | +35-55% | Titanium, Inconel, hardened steel | 1,650°F |
| Diamond (CVD/PCD) | +100-200% | Aluminum, composites, graphite | 1,200°F |
For in-depth coating comparisons, see our Tool Coating Selection Guide.