A finish can improve corrosion resistance, wear, conductivity, cleanliness, or appearance—but it can also change dimensions and highlight cosmetic variation. The right specification starts with the job the surface must do.
Choose the finish from the operating requirement first, then confirm coating thickness, masked areas, cosmetic expectations, and the dimensions that apply after finishing.
01
Define what the finish needs to accomplish
List the primary requirement before naming a process. Corrosion protection may suggest anodizing, passivation, plating, or conversion coating depending on the base material. Wear surfaces may need a harder treatment, while electrical contacts may require controlled conductivity and selective masking.
Appearance should be specified separately from protection. Color targets, gloss, visible grain direction, rack marks, and acceptable shade variation all affect how a finishing supplier plans the work.
02
Match the finish to the base material
Aluminum is commonly anodized for corrosion resistance and appearance. Stainless steel is often passivated to restore a clean protective surface after machining. Carbon steel may use zinc or nickel plating, black oxide, paint, or powder coat depending on exposure and wear. Brass and copper require extra attention where conductivity or cosmetic aging matters.
Not every alloy responds identically. Welds, inserts, mixed alloys, and areas affected by heat can create visible color differences after treatment. Identifying these conditions early makes the final result more predictable.
03
Account for dimensional change
Coatings add thickness, and conversion processes can alter the surface in different ways. Threads, press fits, bearing bores, sealing lands, and grounded electrical contacts may need masking or machining allowances.
State whether a tolerance applies before or after finishing. For a close fit, the finished condition is usually what matters. Sharing the mating component or fit requirement helps the manufacturing team choose a practical allowance.
- Identify surfaces that must remain electrically conductive
- Mark threads, bores, and contact faces that require masking
- Define cosmetic class and the surfaces visible in assembly
- Approve a physical sample or color range when appearance is critical
04
Write an unambiguous finishing note
A useful note includes the finish process, applicable standard, type or class, color when relevant, thickness range, masked areas, and any required testing. Avoid relying only on a color name; the acceptable range should be tied to a recognized sample or specification.
If the part has both critical dimensions and a cosmetic requirement, discuss them together during quotation. That lets machining, finishing, and inspection be planned as one controlled route rather than three disconnected steps.
