Letter 7086

Pitch Diameter increase of zinc plated threaded parts 

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We are applying .0002" to .0003" of zinc plating to threaded parts. The pitch diameter of the part before plating was .279" and after plating was .282" which indicates a total build-up of .003". I have been told that the pitch diameter increases by a factor of 4, 6, or 8 but no one is sure by which factor the pitch diameter increases. The mean thickness of the plating was .00038" and if mulitplyed by a factor of 8, i can see where the pitch diameter increases by a factor of 8. I need to figure out how the pitch diameter is affected by plating thickness to determine if I can plate the parts to specification and still fit the thread gauge. Can anyone tell me by which factor the pitch diameter increases and why? Any help would be greatly appreciated.

Chris McCain, Q.A. Manager
Techtrix, Inc. - Gadsden, Alabama

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There are at least partial answers to your inquiry on the following three letters, Chris: 2906, 22409, 31694.


Ted Mooney, P.E. 
finishing.com
Brick, New Jersey

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