• Topic 51293 "Zinc plating blind holes / threaded holes"

A. Hi Kumar. The major diameter, i.e., the outside diameter, increases by 2X the plating thickness --as with any other outside diameter, or any measurement which includes plating on both sides.

The pitch diameter increases by 4X the plating thickness because in addition to the plating on both sides of the diameter, as previously mentioned, there is plating on both flanks of the thread.

Luck & Regards,

A. I believe that I would start by seeing what gage fits the mating screw part. Do you have a system for incoming screws?

When you are confident that your mating screw is under control, I would see how they fit the internal thread of the collar screw, both before and after plating.

You should be able to find some combination which gives you the fit that you want. Then you can set up the acceptance criteria for the collar.

You may find that your incoming mating parts need as much help as the collars.

A. Allen,

Most plating solutions will not plate an ID more than one diameter deep. When you put threads with their high current density areas on each thread it makes it even more difficult. This is very obvious if you have them color chromated and have a small bright light.

You will go thru many platers until you find one that has considerable experience with this type of fastener and has learned how to cheat the system.

It is further a pain because it is a small blind hole, so will retain solution even with excessive rinsing.

In short, a nasty part to economically plate in bulk.

A. Semantics: E-coat is a painting process, not an electroplating process. Having never seen it on nuts, I would be shocked if you could maintain the 0.0002" tolerance you mentioned. Not knowing how uniform the paint will attach to the various sections of the thread, it would be impossible to say how to cut the thread. If it were electroless nickel, you would simply subtract that amount from your thread and truncate the top by double the plate amount.

A. Hi. The e-coat electrolyte is conductive, but once the paint electrochemically reacts as it deposits, it becomes insulative. That's good because it leads to a relatively uniform deposit thickness, rather like electroless nickel. So James' comment on electroless nickel should be generally applicable.

Luck & Regards,

A. Plug the holes before plating. Even easier, make the holes after plating. If you must have plating on the threads, use a slightly oversize tap to allow for the build-up of plating.

A. If you are plating with a relatively soft metal you can use a roll tap to open up the hole without removing all of the plating.

A. Dear Gurbaran,

Please check what kind of tolerance gauge you are using. Before plating the gauge for checking to be used 6G, and after plating the gauge to be used 6H.

A. Hi, Tonya.

In a way, the cart is before the horse here, because the problem is not so much gaging the part or measuring anything before plating, as much as it is determining the plating specifications and the capability of the plating process. Internal threads generally don't plate well (sometimes not at all in the root) unless you have made some special provisions for it. These sound like precision fasteners that you would not barrel plate, but I hate to make that assumption. If they are rack plated, an internal anode may be practical, although expensive.

You need to find out (or decide) whether your .0003" minimum applies to the root of the thread or actually only applies to a surface touchable by a 3/4" diameter ball, or whatever. Then, based on the plating practice, you can estimate what the plating profile will look like and what it will do to the dimensions -- it will double the thickness on the threads, etc., and a rule of thumb is that the pitch diameter increases by 4X the plating thickness. Please see if you have any additional info for us. Thanks!

Regards,

A. Good afternoon, Tonya:

It would be best if you had the spec in front of you, along with the blueprint. And it might be a good idea to re-read Ted's response. Otherwise, you might be making a bad assumption.

Plating thickness on nuts is often measured on a flat surface, not the threads. You have to know what's considered a significant surface, and with nuts, the threads may not be -- they may have little or no plating on them at all. And the end user may be expecting that! If you try to compensate by putting 8 microns (0.0003") on the threads, you may be putting a lot more plating on the outer surfaces of the part than necessary, which will just drive up the cost of plating for no reason. And maybe cause some other quality issues.

Another point to consider is whether your plater is using an alkaline or acid plating process; it will affect how plating thickness is deposited on various areas of the part.

This issue should (ideally) be agreed upon in contract review.

One more tidbit: Are the threads deformed after tapping, as part of the locking feature? That would be an obvious issue with gauging.

Have a good weekend.