CNC surface finishes, and how to specify them
A finish is not decoration: it decides corrosion life, wear, electrical contact and whether the part looks like a production component or a prototype. Here are the finishes we run, what each one is for, and the details that have to be on the drawing.
Finishes in regular use
Applied through qualified Shenzhen partners and inspected here before packing, with the certificate checked against the specification on the drawing.
| Finish | Materials | What it gives you | What to put on the drawing |
|---|---|---|---|
| Anodizing, Type II | Aluminum | Corrosion resistance, color, a harder surface | Thickness range, color reference, matte or gloss |
| Hard anodizing, Type III | Aluminum | Wear surface for sliding and handling contact | Thickness range, sealing, areas to be masked |
| Bead blasting or sandblasting | All metals | Uniform matte texture, burr removal, prep before coating | Media type, roughness or a visual sample |
| Brushing | Aluminum, stainless | Directional grain for a machined-metal look | Grain direction relative to the part edges |
| Passivation | Stainless steel | Removes free iron so the surface actually resists corrosion | Standard or customer specification, post-machining only |
| Zinc plating | Steel | Sacrificial corrosion protection for fasteners and brackets | Thickness, trivalent chromate for RoHS, color |
| Nickel plating | Steel, brass, copper | Wear resistance, solderability, appearance | Thickness, bright or satin, areas to be masked |
| Powder coating | Steel, aluminum | Thick, durable color finish for visible parts | RAL code, gloss level, thickness, masking |
| Painting | Metals and plastics | Color at lower cost than powder, thinner film | RAL code, primer, gloss |
| Laser marking | All metals | Part numbers, serials, QR codes for traceability | Content, size, position, contrast or depth |
| Heat treatment | Steel, aluminum, titanium | Hardness, strength, stress relief after heavy machining | Process, target hardness, where it sits in the routing |
Five details that decide whether a finish goes right
Surface before finish. Anodizing and plating show every tool mark. If the part is cosmetic, the Ra callout has to be on the drawing, because no finish hides a 0.8 mm step-over.
Thickness budget. Plating and coating add material. On a thread, a bore or a precision seat that growth matters, so either mask it or specify the finished dimension and let the finisher work to it — but say which.
Masking and contact points. Electrical contact pads, ground points, bearing seats and mating faces usually have to stay bare. Mark them on the drawing; a finisher cannot guess which surface carries current.
Color consistency between lots. Anodized color shifts with alloy, bath and part geometry. Send a physical sample or a color reference if two batches have to match on the same assembly.
Compliance. If the part ships into the EU or North America, specify RoHS and REACH-compliant processes — trivalent chromate rather than hexavalent, for example — and the declaration travels with the certificate.
What we check before packing
Coating thickness, adhesion, color against the agreed reference, and salt-spray performance where the drawing requires it. Parts with a cosmetic face are handled and packed separately rather than dropped into a bulk carton, because a good finish ruined in packing is not a good finish.