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Need plating in tapped holes

I have a part that my company has traditionally electroless nickel plated and we wish to move it to a zinc/yellow chromate process. The part is 1215 carbon steel, about 3" in diameter x 6" long. It is c'bored on both ends about 2.5" deep leaving a 1" thick wall in the center. I have a 5/16-18 tapped hole running through that wall. 1. Will the threads get plated? 2. If not through, how deep? Please advise and thanks for you time.

Wayne Hays
mechanical part designer - Tulsa, Oklahoma
2004

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You didn't tell us the diameter of these counterbores, so I'm having a little trouble picturing the "throw" you would need to get to the tapped through-hole. Further, alkaline zinc plating solutions have better throw than acid zinc, so the type of plating solution will matter. But either way I think I'd be surprised if you can plate the whole length of the counterbore let alone get any plating at all on the threads.

Since it probably won't work without auxiliary anodes and complications, and since you'll be moving into yellow chromate in 2004 when most of the world is moving out, I think you need to investigate the wisdom of this move if it is motivated by cost reduction.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2003

The counter bores are large, approaching 2.38" in diameter in each end of the 3" diameter housing.

Wayne Hays
- Tulsa, OK
2004

Wayne, a generally accepted rule is that plating will go no more than one diameter deep, and that is a point of no plate. Add to this that it is threaded--A high current density on the first thread-- and you reduce this to no more than 1/2 a diameter, or in your case, not much!

James Watts
- Navarre, Florida
2004