Finishes that change dimensions, not just appearance
A finish is a process, and it moves the part. Each guide below covers how the process works, the specification, the dimensional cost — and the applications where the finish is the wrong choice.
Anodized Aluminum: Types, Colors & Tolerances
The standard cosmetic and protective finish for aluminium — hard, corrosion resistant, and it grows the part slightly.
Anodising adds material, not a coating. Expect the surface to grow 50% of the nominal oxide thickness, so a 25 µm layer adds roughly 12.5 µm per surface. A hole becomes smaller and an external feature becomes larger — critical fit dimensions should be masked or machined undersize.
Powder Coating: RAL Colours, Thickness & Limits
A thicker, tougher coating than anodising for parts that need colour and impact resistance — with a size limit worth knowing.
A 60–100 µm film is substantial — far more than anodising. It fills detail, rounds sharp edges and closes small holes. Threads need masking, and a shaft that has to fit into a bearing should be machined undersize or masked.
Bead Blasting: Media Types & Surface Finish
The default prep pass before most finishes — it removes tool marks and gives the coating something to grip.
Light blasting removes a few micrometres and rounds every sharp edge. On a cosmetic part this matters — a 0.05 mm chamfer will be visibly rounded. We increase the edge break before blasting on cosmetic work.
Polished vs Brushed Metal: Finish Comparison
Cosmetic finishing that changes how the part reads rather than how it performs — cheap to add, and easy to over-specify.
Polishing removes a few micrometres of material. On a visible cosmetic face that is negligible, but it is not negligible on a tight fit or a sealing surface.
Stainless Steel Passivation: Standards
A chemical clean that puts the stainless surface back the way the mill intended — required for medical and food-contact parts.
Effectively none — the process removes a molecular layer, not material dimension. This is why it is specified on medical parts where any dimensional change would be a problem.
Electroplating: Zinc, Nickel, Chrome & Specs
A sacrificial corrosion layer with real dimensional cost — the plating thickness belongs in the drawing, not in an assumption.
This is the finish to watch. A 25 µm plating adds 12.5 µm per surface, so a bore shrinks by 25 µm and a shaft grows by 25 µm. Every plated mating dimension has to be called out, and threads need masking or a class allowance.