Mechanical finishes & surface roughness (Ra)
Before any coating, the bare surface itself is a spec. Bead blasting, brushing and polishing each leave a different texture and Ra value, which affects appearance, how coatings adhere, and how sealing surfaces perform. Call out the Ra you need where it matters and leave the rest as-machined.
| Finish | Typical Ra (µm) | Look | Use |
|---|---|---|---|
| As-machined | 1.6 – 3.2 | Tool marks visible | Non-cosmetic parts |
| Bead blasted | 1.0 – 2.5 | Uniform matte | Even base for paint/anodize |
| Brushed (grain) | 0.4 – 1.0 | Directional satin | Visible stainless/aluminum |
| Polished | 0.05 – 0.4 | Bright/mirror | Decorative, sealing, hygienic |
Match finish to metal
- Aluminum → anodize (integral, hard) or powder coat (color, thick).
- Carbon steel → powder coat, paint, or zinc plating — bare steel must be protected.
- Stainless → usually passivate; brush or bead-blast for appearance.
- Copper/brass → polish or clear-coat to hold the finish.