A finish can protect a part, control appearance, or help it fit an assembly. It can also change dimensions. Select the finish with the part’s function in mind, and identify surfaces that must remain free of coating.
As machined and bead blasted
As-machined surfaces retain visible tool marks and are often suitable for internal or functional components. Bead blasting creates a more uniform matte appearance, but it is a cosmetic treatment rather than a substitute for dimensional control.
Anodizing
Anodizing forms an oxide layer on aluminum for improved corrosion resistance and appearance. Color and surface texture can vary with alloy, prior machining, and process. Coating build-up matters on close-fitting bores and threads, so masking or finish allowances may be needed.
Powder coating, plating, and polishing
Powder coating offers a thicker colored surface and is more suitable where its build-up can be accommodated. Plating may be considered for specific electrical, wear, or appearance needs. Polishing changes the visible texture and should be specified by the surfaces that require it.
What to include on the drawing
State the finish, color or texture target, protected surfaces, and any dimensions that apply after finishing. That makes the intended result easier to quote and inspect.
Specify the result, not just the finish name
As-machined, bead-blasted and anodized surfaces serve different functions. Describe the controlled faces, cosmetic zones, color expectation and applicable acceptance method. An as-machined roughness discussion point such as Ra 3.2 µm should be applied only where appropriate; it does not define color, lay, flatness or sealing performance.
A finish note that can be reviewed
Finish / standard: ___
Controlled thickness: ___
Color or approved appearance sample: ___
Masked holes, threads and fits: ___
Roughness on identified faces: ___
Account for dimensions after finishing
Coatings and surface treatments can alter a close-fitting feature. Identify whether inspection occurs before or after the final process. Agree how the final fit, cosmetic appearance and packaging will be accepted, especially when more than one supplier performs the work.