A CNC machined part that looks correct on the bench can fail in service if the surface finish, plating thickness, or corrosion resistance was never called out on the drawing. This gap between "the part looks fine" and "the part will perform for its service life" is where most sourcing disputes begin.
How Plating Changes Your Tolerances
Electroplating and PVD coatings add material to the part surface. A 0.025 mm nickel layer on a brass bushing grows the outer diameter by 0.05 mm when applied radially. Buyers who specify finished dimensions without accounting for that buildup end up with parts that no longer seat in the assembly. The fix is simple: state on the drawing whether dimensions are pre-plate or post-plate, and confirm expected coating thickness with the supplier before the first article ships.
Which Treatment Fits Which Material
Stainless 304 and 316 parts in sensor housings often need no plating at all. Brass and copper sleeves used in plastic molding gates or electronics enclosures may take a thin tin or nickel strike to stop discoloration over time. Aluminum turnings for automation brackets usually receive anodizing rather than electroplating. Specifying the wrong process for the base material can cause adhesion failures that show up only after dozens of field cycles, at which point the cost of a recall far exceeds the extra weeks needed to re-source.
What to Put in Your RFQ
List the coating type, minimum and maximum thickness, salt-spray hours, and whether you need a gauge-based inspection report with the shipment. For annual volumes of 5,000 units, request a first-article inspection that includes beta-ray gauge thickness readings, not just a visual check. Weeda Precision supports drawing-based CNC turning, multi-axis machining, and post-processing on brass, copper, stainless steel, and aluminum, and their quality team issues a dimensional and surface-finish report on every batch so the buyer does not have to chase paperwork separately.
Before sending an RFQ, mark every feature that will be plated and note the exact thickness on the drawing. One line of clarification prevents a rejection report three weeks later.