Surface Finish Calculator

Calculate surface roughness (Ra, µm) based on feed per revolution and tool corner radius. This tool is essential for CNC turning and milling to predict surface quality, optimize machining parameters, and meet engineering requirements.

Surface Finish
Calculator

Type
µm
mm/rev
mm
Surface Finish: 0 µm
Formula: Ra = 46 × f² ÷ r
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Quick Answer

👉 Basic formula:

Ra (µm) ≈ 46 × (f² ÷ r)

  • f = Feed per revolution (mm/rev)
  • r = Tool corner radius (mm)

✔ Example:
f = 0.2 mm/rev
r = 0.8 mm
→ Ra ≈ 2.3 µm

Formula (Surface Finish Calculation)

Standard Turning Formula:

Ra = 46 × (f² ÷ r)

Reverse Calculations (Optional)

  • f = √(Ra × r ÷ 46)
  • r = 46 × f² ÷ Ra

Surface Finish Reference Table

(Example: Corner Radius = 0.8 mm)

Feed (mm/rev) Ra (µm)
0.05 0.14
0.10 0.58
0.20 2.30
0.30 5.18
0.40 9.20

Typical Surface Finish Ranges

Process Ra (µm)
Rough Turning 6.3 – 25
Finish Turning 0.8 – 3.2
Grinding 0.2 – 1.6
Polishing 0.05 – 0.4

How to Use This Calculator

  1. Select calculation type (Ra, feed, or radius)
  2. Enter feed per revolution (mm/rev)
  3. Enter corner radius (mm)
  4. Instantly get surface finish Ra (µm)

✔ Real-time calculation
✔ Useful for CNC turning optimization

Common Engineering Uses

1. CNC Turning Optimization

  • Predict achievable surface finish before machining

2. Surface Quality Control

  • Ensure parts meet drawing requirements

3. Tool Selection

  • Larger radius → smoother finish

4. Process Planning

  • Balance between feed rate and surface quality

Important Notes

  • This formula is idealized, actual Ra depends on:
    • Tool wear
    • Machine vibration
    • Material properties
    • Coolant usage

⚠️ Lower feed → smoother surface
⚠️ Larger radius → better finish

Related Calculators

Enhance your machining workflow:

  • Ra to Rz Calculator
  • Feeds & Speeds Calculator
  • Chip Load Calculator
  • Material Removal Rate Calculator

FAQ

What is surface finish (Ra)?

Ra is the average roughness of a machined surface, measured in micrometers (µm).

Why is surface finish important?

It affects fit, friction, wear, and appearance of parts.

How can I improve surface finish?

  • Reduce feed rate
  • Increase tool radius
  • Use finishing passes

Is this formula exact?

No, it provides an engineering estimate, not an exact value.

What unit is Ra measured in?

Typically µm (micrometers).

CNC Machining Shops

CNC Machining Shops

Need Precision Surface Finish CNC Machining?

urface finish directly impacts part performance and quality.

👉 We offer:

  • CNC machining with controlled surface finish
  • Finishing processes: grinding, polishing, anodizing
  • Ra control down to 0.4 µm or better
  • Inspection reports available

Upload your drawing today and get a precision machining quote.