Plating

An adequate plating note must clearly set forth whether dimensions apply before or after plate, type of plate, the minimum and maximum thickness, specific location where thickness will be checked, any tests to which plate will be subjected and finish appearance, if important. See Drawing #35 for a sample plating call out.

If the drawing carries after-plate dimensions, always show the before-plate dimensions for threads, groove widths and corners. Keep in mind that plating builds up at nearly a 2:1 ratio on sharp edges and corners, and at 4:1 on thread pitch diameters. This is a seeming oddity, but nevertheless true. Plating a thread can restrict already close tolerances. Any micro-finish note must be qualified as to whether it applies before- or after-plate. A before-plate low reading can double after plating. If an after-plate micro-finish is stipulated, the supplier may be obliged to generate a substantially better before-plate surface at a considerably higher cost.

Good practice on external threads that are to be plated is to specify class 2A before coating and 3A after plating. Many prints show class 2A with a note on the print that "All dimensions apply after plating." This defeats the purpose of class 2A which is to have an allowance for plating.

If dicromate dip is required, either specify the preferred color if you have one, or leave the choice up to the supplier. Many colors are available.

Deep or blind holes will not take plate except by special — and very expensive — processes. On such parts, clearly designate if holes are to be fully plated.

On most electronic and military specifications the plating thickness applies to any area that can be touched by a ¾" diameter ball.

If racking is required, point of clamping or contact must be specified.

plating drawing