CNC Surface Finish Guide:
Stop over-specifying. Learn when to use Ra 3.2 (As-Machined) vs Ra 0.8 (Polished) to save 20-30% on production costs.
The most common cost-driver we see on technical drawings is an unnecessary global surface finish callout (e.g., "All surfaces Ra 0.8"). While this looks good on paper, it forces secondary operations like grinding or manual polishing.
Understanding Ra (Roughness Average)
Ra measures the average height of microscopic peaks and valleys on the metal surface. Lower numbers = smoother surface = higher cost.
Fig 1: Relative Cost Impact of Surface Finishes.
Standard "As-Machined" (Ra 3.2 - 1.6)
Contrary to popular belief, "As-Machined" does not mean rough. Modern high-speed CNC mills produce a clean, uniform finish suitable for:
- • Internal brackets and hidden components.
- • Mounting surfaces.
- • Parts undergoing Powder Coating later.
Cosmetic & Functional Finishes
| Finish | Ra Value | Best Application |
|---|---|---|
| Bead Blast | N/A (Matte) | Hiding tool marks, uniform matte look. |
| Anodizing Type II | No change | Color, corrosion resistance (Aluminum). |
| Vapor Polish | Optical Clear | Polycarbonate lenses, light pipes. |
Check our Parts Gallery to see high-res examples of these finishes on real aluminum and plastic parts.
Unsure what to specify?
Upload your drawing. Our engineers will suggest the most cost-effective finish that meets your functional requirements.
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