Finish & Coating Guide

The most common gap on an incoming finishing print is a color and nothing else. “Black, semi-gloss” does not identify a product we can buy, and two blacks of different chemistries can behave completely differently once the part is in service. To quote and purchase against, we need:

• Chemistry — polyester, epoxy, epoxy-polyester hybrid, and so on. This is what drives UV and weather resistance, chemical resistance, hardness, and cure schedule. An epoxy that is excellent indoors will chalk outdoors.
• Manufacturer or brand — powders are not interchangeable between suppliers, even at the same color reference.
• Product name or number — the specific stock code.
• Gloss level, and a physical color standard where appearance matters.

Put it on the drawing the same way you would call out a resin or an alloy. If you genuinely do not have a preference, tell us the service environment — indoor or outdoor, UV exposure, chemicals, handling — and we will quote something appropriate and name it on the quotation so you know exactly what you are approving.

Cosmetic class: Wrex quotes and runs Class B powder coating. Our pricing reflects Class B only. If your part needs a Class A cosmetic or show-surface finish, raise it at RFQ — a Class A expectation held against a Class B quote is one of the most common finishing disputes there is, and it is entirely avoidable by saying so up front.

Two finishing choices on the same surface can rule each other out, and it is cheaper to know before the router is written than after the first article:

• Ball burnishing and powder coating are mutually exclusive. Burnishing work-hardens and polishes the surface, and powder will not key into it. Choose one or the other per surface — a bright burnished finish, or a coated one.
• Vibratory deburring is fine ahead of powder coating. It is a common and useful prep step; only burnishing conflicts.
• Every powder-coated part needs a hanging point — a hole or feature it can be racked from through spray and cure. If the part has none, a fixture has to be designed, and that cost lands on the quote.

Every surface that must stay uncoated needs a mask, and masks are labor. A part with three simple masked flats costs meaningfully less to finish than the same part with a recessed thread and a blind bore that both need plugs. Common exclusion zones:

• Threads — coating changes effective thread fit; almost always masked or chased after coating.
• Bearing bores and press-fit diameters — film thickness eats the interference fit.
• Ground/bonding contacts — powder coat is an insulator; electrical continuity points must stay bare.
• Sealing faces — gasket surfaces usually need the as-machined flatness.
• Datum surfaces — anything used to locate the part downstream.

Design tip: where you can, put exclusion zones on accessible external flats rather than recesses or internal features. It is the single cheapest finishing decision available to you, and it costs nothing at design stage.

Powder coating typically adds about 0.002–0.004 in per coated surface, which means a 0.004–0.008 in change across a bore or a slip fit. If a dimension is toleranced tighter than that and the surface is coated, either the dimension needs to be called out after coating, or the feature needs to be masked and/or machined post-coat. Conversion coatings are thin enough that this rarely matters.

Send a physical sample whenever color matters. RAL and Pantone references get close, but gloss level, texture, and substrate all shift perceived color — two parts at the same RAL number in different gloss levels will not look like a match on an assembly. We confirm against an approved physical standard before running production.

Related

• Powder Coating capability
• Custom Finishing capability
• Die Cast Finishing & Powder Coating
• Blog: Powder coating design and masking considerations