Letter 2906

Plating external threads 

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I have a plating problem. I need to plate clear zinc chromate on a 12l14 steel nut with a .563-24 unef- 2A external thread. The plating to be .0001 - .0003 thick. What is the preplate pitch diameter. Also what is the formula for calculating preplate pitch diameters?

Kemp Weekes
- Mansfield, OHIO

We plate cadmium on threaded parts every day and usually to a thickness of .0003/.0006. The ratio is four to one on threads, so you can anticipate a .0004 to .0012 change in the pitch diameter of the thread. The functional element of the thread is going to grow with plating since the 30 degree angle of the thread is plated non-uniformly. (Major diameter builds faster than the minor diameter), therefore you should look for a thread which is at least .002 under the maximum after plate dimension. We typically plate class three threads and NS with only .0015 tolerance, so with a class 2 your customer should have no problem holding size to the low side. Remember,The slower the plating rate, the better uniform deposition. Good luck..

Tim Martin
plating shop - Springfield, MA

Need a math calculation for measuring the final Pitch Diameter of a Unified Vee form thread configuration when a Cadmium Plating thickness is called out to be applied to each surface of the flank thread configuration.

Example: if a .0005 inch Cadmium is applied to each surface of the thread of the bolt thread how do I calculate the final Pitch Diameter of the bolt after plating and when different thickness call outs are required?

I need this information as a training reference and inspection aid for Quality and Manufacturing Engineers.

Thank you for your kind help.

Andrew A. Bemak, Jr.
Machine Shop - Cleveland, Ohio, United States

Andrew, See the Machinery's Handbook. I have edition 24 and it is on page 1576. Listed under "Dimensional Effect of Coating" in the section dealing with threads.

Kevin Davis
Automotive OEM - Versailles, KY, USA

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Ed. note: The following letters also seem to offer insight into thread allowances for plated parts: 22409, 31694.

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