Surface Roughness Guide

Understanding surface roughness specifications and how they impact part performance, appearance, and manufacturing costs.

Surface Roughness Options

Standard (Ra 3.2μm)

Included

Standard CNC machined finish suitable for most applications

Characteristics:

  • Visible tool marks
  • Good for non-critical surfaces
  • Economical option
  • Adequate for most functions

Best For: General parts, prototypes, internal components

Smooth (Ra 1.6μm)

££

Finer finish with reduced tool marks for improved appearance

Characteristics:

  • Reduced tool marks
  • Better appearance
  • Suitable for sealing surfaces
  • Improved friction properties

Best For: Sealing surfaces, visible parts, sliding components

Polished (Ra 0.8μm)

£££

Very smooth finish approaching mirror-like quality

Characteristics:

  • Minimal surface texture
  • Excellent appearance
  • Low friction
  • Easy to clean

Best For: Molds, medical devices, food equipment, optical parts

Price Guide: £ = Budget-friendly | ££ = Moderate | £££ = Premium | ££££ = Specialist

Understanding Ra Values

Ra (Roughness Average) is the most common parameter for measuring surface roughness. It represents the average deviation of surface peaks and valleys from the mean line, measured in micrometers (μm).

Practical Comparison

  • Ra 12.5 μm: Very rough, like coarse sandpaper
  • Ra 6.3 μm: Rough machined surface
  • Ra 3.2 μm: Standard machined finish (our standard)
  • Ra 1.6 μm: Fine machined finish
  • Ra 0.8 μm: Very smooth, polished
  • Ra 0.4 μm: Mirror-like finish

Surface Roughness by Process

Manufacturing ProcessTypical Ra (μm)Surface Quality
Rough Machining6.3 - 12.5Visible tool marks, rough
Standard CNC Milling1.6 - 3.2Good finish, slight marks
Fine CNC Milling0.8 - 1.6Smooth, minimal marks
Precision Turning0.4 - 1.6Very smooth
Grinding0.2 - 0.8Excellent finish
Polishing0.1 - 0.4Mirror-like
FDM 3D Printing6.3 - 25Visible layer lines
SLA 3D Printing1.6 - 6.3Smooth surface

Roughness Selection by Application

When to Choose Standard (Ra 3.2μm)

  • General purpose parts
  • Non-critical surfaces
  • Cost-sensitive projects
  • Internal components

When to Choose Smooth (Ra 1.6μm)

  • Sealing surfaces
  • Sliding or moving parts
  • Customer-facing surfaces
  • Parts requiring coating

When to Choose Polished (Ra 0.8μm)

  • Medical devices
  • Food processing equipment
  • Optical components
  • Mold surfaces

Impact on Performance

  • Friction: Smoother surfaces reduce friction
  • Sealing: Smooth surfaces improve seal quality
  • Wear: Polished surfaces last longer
  • Cleaning: Smoother is easier to clean

Price Guide: £ = Budget-friendly | ££ = Moderate | £££ = Premium | ££££ = Specialist

Understanding Ra Values

Ra (Roughness Average) is the most common parameter for measuring surface roughness. It represents the average deviation of surface peaks and valleys from the mean line, measured in micrometers (μm).

Practical Comparison

  • Ra 12.5 μm: Very rough, like coarse sandpaper
  • Ra 6.3 μm: Rough machined surface
  • Ra 3.2 μm: Standard machined finish (our standard)
  • Ra 1.6 μm: Fine machined finish
  • Ra 0.8 μm: Very smooth, polished
  • Ra 0.4 μm: Mirror-like finish

Surface Roughness by Process

Manufacturing ProcessTypical Ra (μm)Surface Quality
Rough Machining6.3 - 12.5Visible tool marks, rough
Standard CNC Milling1.6 - 3.2Good finish, slight marks
Fine CNC Milling0.8 - 1.6Smooth, minimal marks
Precision Turning0.4 - 1.6Very smooth
Grinding0.2 - 0.8Excellent finish
Polishing0.1 - 0.4Mirror-like
FDM 3D Printing6.3 - 25Visible layer lines
SLA 3D Printing1.6 - 6.3Smooth surface

Roughness Selection by Application

When to Choose Standard (Ra 3.2μm)

  • General purpose parts
  • Non-critical surfaces
  • Cost-sensitive projects
  • Internal components

When to Choose Smooth (Ra 1.6μm)

  • Sealing surfaces
  • Sliding or moving parts
  • Customer-facing surfaces
  • Parts requiring coating

When to Choose Polished (Ra 0.8μm)

  • Medical devices
  • Food processing equipment
  • Optical components
  • Mold surfaces

Impact on Performance

  • Friction: Smoother surfaces reduce friction
  • Sealing: Smooth surfaces improve seal quality
  • Wear: Polished surfaces last longer
  • Cleaning: Smoother is easier to clean

Contact Our Expert Engineers

Unsure which surface roughness specification is right for your application? Our engineering team can help you select the optimal finish for your performance, appearance, and budget requirements.

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