Feed & Speed: Quick CNC Essentials

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Every CNC beginner asks: “What’s the optimal feed and speed?”

Answer:“It depends.”→ No universal setting exists. Success hinges on balancing variables unique to your setup.

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⚙️ Key Factors:  

  • Machine rigidity & spindle power  
  • Tool quality & material hardness  
  • Workholding stability  
  • Desired finish + tool life  
  • Depth of cut (DoC) & Width of cut (WoC)
feed and speed DOC WOC visual depiction

No magic formula → Use rules + tweak  

🔬 The Science: Surface Speed & Chip Load

1. Surface Speed (Vc):

  • What: Linear speed (m/min) of the cutter’s edge through the material.
  • Why: Determines heat generation. Too slow → rubbing; too fast → overheating.
  • Rule: Constant per material (e.g., Aluminum: 120–250 m/min; Hardwood: 300–600 m/min).

2. Chip Load (fz):

  • What: Thickness (mm) of material each tool flute removes per revolution.
  • Why: Controls cutting force & chip evacuation. Too low → heat; too high → tool breakage.
  • Rule: Constant per material (e.g., Aluminum: 0.08–0.15 mm/tooth; Plywood: 0.2–0.4 mm/tooth).

💡 Key Insight:

  • Surface speed & chip load are material properties.
  • Tool diameter/flute count convert these into RPM & feed rates.

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Workflow: From Theory to Action

  1. Get Baseline Values:
    • Use material-specific charts (e.g., Sandvik Coromant) or the MIT Calculator.
    • *Example: 6mm carbide end mill in aluminum → Vc=180 m/min, fz=0.1 mm/tooth.*
  2. Calculate RPM & Feed Rate:
    • RPM = (Vc × 1000) ÷ (π × Tool Diameter)
    • Feed Rate (mm/min) = RPM × Flutes × fz
    • *Or skip math: Plug Vc + fz into Fusion 360’s tool library → auto-generates values.*
  3. Tweak for Your Setup:
    • Start at 70% of recommended values.
    • Test-cut on scrap → observe chips/sound/finish → adjust.
feed and speed calculation from surface speed and cheap load

CNC VOX Surface Speed and Chip load

Material Surface Speed (Vc)
(m/min)		 Min Chip Load (fz)
(mm/tooth)		 Max Chip Load (fz)
(mm/tooth)
Hard Wood 339 0.15 0.45
Soft Wood / Ply 230 0.25 0.45
MDF 339 0.20 0.40
Soft Plastics 137 0.10 0.20
Hard Plastics 100 0.30 0.40
Aluminium 160 0.10 0.15
Feed and speed sweet spot

🚦 Troubleshooting (Read the Cut)

Symptom Cause Fix
Squealing Rubbing (↓ chip load) ↑ Feed Rate OR ↓ RPM
Chatter Tool deflection ↓ Feed Rate OR ↓ DoC
Burning Excessive heat ↑ Feed OR ↑ RPM OR coolant
Tool Breakage Overload ↓ Feed OR ↑ RPM OR ↓ DoC

⚡️ Why Optimization Matters

  • Cost: Broken tools + wasted material = $ lost.
  • Time: Sanding burns/tear-out > dialing in settings.
  • Quality: Surface finish = professional vs. amateur.
  • Safety: Snapped tools = dangerous projectiles.

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✅ The Takeaway

  1. Start with science: Surface speed + chip load.
  2. Respect your machine: Rigidity/power dictate limits.
  3. Tweak methodically:
    • Adjust feed rate first (most impact on chip load).
    • Log settings → build a personal database.
  4. Let software help: Fusion 360 + MIT Calculator = 90% solved.

“Good settings turn CNC from frustration to flow.”

Tools:

feed and speed sweet spot