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

There is no magic formula. Instead, use rule of thumb & tweak  

🔬 The Science: Surface Speed & Chip Load

What you need is Surface speed and Chip load. Feed and Speed is derived from this information for any tool diameter or shap.

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 is what you need for each material.
  • Tool diameter/flute count is used to derive RPM & feed rates from surface speed & chip load.

Workflow: From Theory to Action

  1. Get Baseline Values:
    • Use material-specific charts (e.g., 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 339 0.25 0.45
MDF 339 0.20 0.40
Soft Plastics 339 0.15 0.25
Hard Plastics 339 0.10 0.20
Aluminium 160 0.10 0.15
Alu (coated) 280 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 or MIT Calculator

“Good settings turn CNC from frustration to flow.”

Tools:

feed and speed sweet spot