Speed & Feed Calculator

RPM calculation is fundamental to successful CNC machining and depends on cutting speed (SFM/m/min) and tool diameter:

RPM Calculation Formulas

• Metric System: RPM = (Cutting Speed m/min × 318.3) ÷ Tool Diameter (mm)
• Imperial System: RPM = (SFM × 3.82) ÷ Tool Diameter (inches)

Practical Examples

• 12mm end mill in aluminum at 300 m/min: (300 × 318.3) ÷ 12 = 7,958 RPM
• 0.5" end mill in steel at 200 SFM: (200 × 3.82) ÷ 0.5 = 1,528 RPM
• 6mm drill in stainless at 80 m/min: (80 × 318.3) ÷ 6 = 4,244 RPM

Key Considerations

• Material Hardness: Harder materials require lower cutting speeds
• Tool Material: Carbide tools run 3-5x faster than HSS tools
• Operation Type: Roughing uses lower speeds, finishing allows higher speeds
• Machine Limitations: Never exceed spindle speed or power limitations

Pro Tip: Always start with conservative parameters and gradually increase based on results and tool wear monitoring.

Feed rate selection is critical for tool life, surface finish, and productivity across different machining operations:

Milling Feed Rate Formula

Feed Rate = RPM × Number of Flutes × Chip Load per Tooth

Typical Chip Loads by Material

• Aluminum Alloys: 0.05-0.25mm/tooth (0.002-0.010 in/tooth)
• Carbon Steel: 0.025-0.15mm/tooth (0.001-0.006 in/tooth)
• Stainless Steel: 0.02-0.1mm/tooth (0.0008-0.004 in/tooth)
• Cast Iron: 0.03-0.2mm/tooth (0.0012-0.008 in/tooth)
• Titanium: 0.01-0.08mm/tooth (0.0004-0.003 in/tooth)

Operation-Specific Feed Rates

• Turning - Roughing: 0.1-0.5mm/rev (0.004-0.020 in/rev)
• Turning - Finishing: 0.05-0.2mm/rev (0.002-0.008 in/rev)
• Drilling: 0.05-0.3mm/rev depending on diameter and material
• Threading: Feed = Thread pitch (synchronized with spindle)

Important: Always start with conservative feeds and increase based on machine capability, tool condition, and required surface finish.

Material properties have a profound impact on optimal machining parameters and tool selection:

Key Material Properties

• Hardness: Directly affects cutting speed (harder = lower SFM)
• Work Hardening: Materials like stainless steel require constant chip load
• Thermal Conductivity: Affects heat dissipation and allowable speeds
• Machinability Rating: Baseline comparison for parameter selection

Typical SFM Ranges by Material

• Aluminum 6061-T6: 500-1500 SFM (150-450 m/min)
• Carbon Steel (1018-1045): 100-400 SFM (30-120 m/min)
• Stainless Steel 316: 80-200 SFM (25-60 m/min)
• Tool Steel (4140 HT): 50-150 SFM (15-45 m/min)
• Titanium Ti-6Al-4V: 50-150 SFM (15-45 m/min)
• Inconel 718: 30-100 SFM (10-30 m/min)

Material-Specific Considerations

• Aluminum: High thermal conductivity allows aggressive parameters, watch for built-up edge
• Stainless Steel: Work hardens rapidly, maintain constant feed, use sharp tools
• Titanium: Low thermal conductivity, requires flood coolant, sharp cutting edges
• Cast Iron: Abrasive material, use ceramic or CBN tools for production

Use our calculator's material database for specific recommendations based on your exact alloy and heat treatment condition.

Understanding the differences between conventional and climb milling is crucial for optimal parameter selection:

Conventional Milling (Up Milling)

• Tool Rotation: Against the feed direction
• Chip Formation: Starts at zero thickness, increases to maximum
• Forces: Tends to lift workpiece, requires more clamping force
• Machine Requirements: Works with machines having backlash
• Applications: Older machines, interrupted cuts, thin workpieces

Climb Milling (Down Milling)

• Tool Rotation: With the feed direction
• Chip Formation: Maximum thickness at start, decreases to zero
• Forces: Pushes workpiece down into fixture
• Machine Requirements: Requires rigid machine with ball screws
• Applications: Modern CNC machines, best surface finish

Parameter Differences

• Feed Rates: Climb milling allows 20-50% higher feed rates
• Tool Life: Climb milling typically provides longer tool life
• Surface Finish: Climb milling produces superior surface finish
• Power Requirements: Conventional milling requires 10-15% more power

When to Use Each Method

• Use Climb Milling: Modern CNC machines, best finish required, production runs
• Use Conventional: Older machines with backlash, very thin workpieces, interrupted cuts

Recommendation: Modern CNC machines should use climb milling whenever possible for optimal results.

Optimizing speeds and feeds requires balancing tool life, productivity, and part quality through systematic approach:

Taylor Tool Life Equation

VT^n = C where V = cutting speed, T = tool life, n = material constant, C = constant

• Principle: Small speed increases dramatically reduce tool life
• Application: Doubling speed typically reduces tool life by 75-90%
• Optimization: Find the speed that minimizes cost per part, not per minute

Systematic Optimization Process

• Step 1: Start with manufacturer's recommended parameters
• Step 2: Run test parts and monitor tool wear patterns
• Step 3: Adjust one parameter at a time based on results
• Step 4: Document optimal parameters for each material/operation

Tool Wear Pattern Analysis

• Excessive Flank Wear: Reduce cutting speed by 10-20%
• Edge Chipping: Reduce feed rate or increase cutting speed
• Built-up Edge: Increase cutting speed or reduce feed rate
• Crater Wear: Reduce cutting speed and improve cooling

Productivity Enhancement Strategies

• Target 70-80%: Of maximum recommended parameters for optimal balance
• Coated Tools: Allow 20-50% speed increase over uncoated
• Adaptive Control: Use real-time force/power monitoring for optimization
• High-Efficiency Milling: Use larger axial depths with smaller radial engagement

Key Insight: The goal is minimizing cost per part, which includes tool cost, machine time, and part quality - not just maximizing cutting speed.