Brushed, Polished and Bead Blasted: Specifying Mechanical Finishes

Mechanical finishing is the step that decides what a profile looks like underneath everything else. Anodizing and coating are largely transparent to what they cover: they reproduce the surface they were given, and they reproduce its defects just as faithfully.

Mechanical finish comes before everything else

A scratch, a die line or a handling mark that survives preparation will be visible in the finished part, and usually more visible than it was on bare aluminum — a bright specular surface draws the eye to interruptions that a matte one hides.

This is the reason to settle the mechanical finish early. It sets how much material the polishing or blasting step has to remove, and therefore whether a die line is a cosmetic detail or a rejection.

Brushed finishes and grain direction

Brushing is a directional abrasive finish. The grain is part of the specification: two panels with identical roughness but opposite grain direction read as mismatched when they meet at a corner, especially on a reflective surface.

On a door frame or a handle, directional grain and the direction the hand travels is a design decision. Say which direction, and say whether visible grain direction changes between adjacent parts are acceptable.

Polished finishes

Polishing produces the brightest surface and is the least forgiving. Extrusion marks must be removed by the polishing step, so the amount of material removal is real. Polished aluminum also shows fingerprints, dust and any handling that happens after finishing.

For architectural work, polished surfaces are usually specified only where the design intent depends on mirror-like appearance and where cleaning will actually happen.

Bead blasted and etched finishes

Blasting produces a uniform matte surface and is the most effective at hiding minor marks. The result depends on the media, the pressure and the distance — two shops both offering “bead blasted aluminum” can hand back visibly different surfaces.

Where the matte texture matters to the design, specify the media or the resulting roughness rather than the process name alone.

Mechanical finish under anodizing

Anodizing amplifies mechanical texture rather than smoothing it. A brushed surface becomes a brushed anodized surface; a blasted one stays matte. Etching before anodizing removes some material and produces a satin appearance that is more uniform than brushing, at the cost of a slight dimensional change.

If the final appearance matters, the mechanical finish and the anodizing step have to be specified together. Choosing them in sequence — mechanical finish first, then anodizing — usually produces a part nobody designed.

Writing the requirement

• Name the finish and, where it is directional, the direction.
• Give a roughness figure when texture is a design element, not just a process name.
• State which faces are cosmetic and which may retain extrusion marks.
• Approve a sample produced on the same alloy and the same sequence as production.
• Say whether the surface will be anodized afterward, so the finish step can be sized for it.

From Design Review to Quotation

Chengdacai supports custom aluminum extrusion, precision cutting, CNC machining, drilling, tapping, brushing, polishing, blasting, anodizing and powder coating. A complete drawing package lets the engineering team identify tooling, secondary operations and quality controls before production starts.

See our mechanical finishes reference for the process range, and anodizing thickness specification if the part will be anodized after finishing.

Explore our aluminum door handles, profile hinges, custom aluminum profiles, or send your drawing for an engineering review.