Cad plating thickness on close tolerance diameters 2

[damc]

I consistently run into dimensioning problems on parts required to have Cad Plating per QQ-P-416 on close tolerance
diameters.(.0005 inch or less)My question is: How can you allow a tolerance for plating without effectivly eliminating most of the tolerance for machining? For Example, Class 3 plating is .0002 minimum per side or .0004
on the diameter. If you allow only .0003 maximum plating per side you wind up with a variation of .0004 to .0006 on the diameter for the plating itself. with .0003 tolerance for machining.

 

[jbel]

Why not call out a minimum plating depth also? I know this is tight but you could call out .0002 min and .0003 max therefore the plating doesn't eat up all your tolerance.

 

[Nate101]

Damc,
This is typical with a lot of plating and anodizing. When the tolerances don't allow for a lot of tolerance overlap, I'll plan to machine more material of the features the minimum alowable plating thickness, cut my machining tolerances down and hold the platers to the tightest tolerance they can hold. The plater is your variable, the manufacturing you can control. If the plater can't hold what I want, then I'll add an operation to hone, machine or grind the features in.

 

[ncassist]

One other option I occaisionaly use, ask engineering about specifying the part be final bored after plating, then a brush coating of something like a chem film for aluminum to protect the final cut surfaces.

 

[kenvlach]

If the parts’ geometries are suitable, considering mechanical plating Cd per ASTM B696 or vacuum deposition per ASTM B699.

A consistent QC problem is easier to solve than an inconsistent one.
With electroplating, thickness always varies with current density. This variation can be determined using test panels in Hull plating cells, or by empirical measurements on parts. If the plater is consistent, tracking results should enable you to predict the decrease in thickness within ID’s as a function of diameter & depth (start with QQ-P-416F, Amendment 3, Para. 3.3.1), and make specifications accordingly. Alternatively, maintain the current density within IDs with auxiliary anodes passing through the bore of critical parts. In any event, you and your plater should be able to handle a ‘consistent dimensioning problem.’

A final honing is often specified on hard anodized parts and worn parts rebuilt via heavy Cr plating to get exact dimensions and smoothness. I just don’t like the idea with Cd due to its toxicity (EPA & OSHA concerns).