8 MIN READ · SURFACE TECH INDUSTRIES
Most re-spec cycles on anodized parts don't come from the anodizing process itself — they come from drawing decisions made before the part ever reached the line. A handful of details, addressed at the design stage, save a round trip back to engineering.
Anodic coating grows roughly half into the base metal and half out of it — it isn't purely additive on the outside surface. On tight-tolerance features (bores, shafts, mating surfaces) this build-up needs to be designed into the tolerance band from the start, especially for Type III hard anodizing where the coating is thickest. A part machined to final dimension and then anodized to a hard-anodize spec will come out oversize or with an interference fit that wasn't intended.
Every part needs an electrical contact point to anodize — the rack mark left at that point will show a thin or absent coating and a visible witness mark. If the drawing doesn't specify where that contact point can go, the processor picks the most convenient spot, which may land on a cosmetic or functionally critical surface. Calling out an acceptable rack-mark zone on a non-critical surface avoids a rejected lot over a mark that was never actually a functional problem.
Threads, precision bores, datum surfaces and any area that will be adhesively bonded or requires electrical continuity often need to be masked off before anodizing. "Anodize per MIL-A-8625" without a masking callout leaves that decision to whoever runs the job. Explicit masking instructions on the drawing — which threads, which bores, to what depth — remove the ambiguity.
None of this is exotic — it's the handful of details that, called out on the drawing up front, keep a part from bouncing back for rework after the first article comes off the line.
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