Electroless Nickel Plating

What is nice about electroless nickel is that there is no electrolytic throwing issues. If the parts gets in contact with fresh EN solution the process occurs. You do not mention if these are blind holes, if so then there must be a mechanical means to move the part so the holes get filled with the solution and continues to see fresh solution during the complete process. You mention rust so keep in mind that the part must be properly cleaned and rinsed before going into the EN bath. You also do not mention if this is a process you presently do in house or send out to a metal finisher.

Thanks for the reply. The magnetic iron is in the form of plates of approx. 50 mm x 14 mm x 8 mm with blind holes on two sides. We are presently sending the pieces to a metal finisher. I assume that in case we use some mechanical means to move the part, the areas of the components which are in contact with the fixture used for the mechanical movement may not get exposed to the EN bath solution. Can we agitate the EN bath solution itself instead of mechanical movement of the components? Please advise.

Hard to say in any event you need to get the blind holes filled with solution and continue to flush fresh solution into the holes. With blind holes you have air entrapment preventing the EN solution from getting in there. If there was no issue with blind holes then the answer would be , "yes" you can agitate the solution typically with 10x filtration and air spargers. Regarding the contact points from the fixture you need to use a fixture that allows some movement of the part and the EN will cover those points. If you are using a fixed contact fixture or rack as you would for electrolytic plating then you may end up with contact marks.

You are asking for trouble. If the threads are plated, a bolt may not fit anymore. I had a problem plating brass turnbuckles for the Navy, they like chrome. The plated threads would not go together anymore, and when I tried to run a die over the male threads, it tried to remove the chrome,(of course), looked like hell, and dulled the die, chrome is hard! Re-tapping the female holes did not go easy, either.

I don't know of an oversize tap that would make room for plating on the threads. A tapped hole with a bolt in it should not rust.

You should be able to put a rust preventer in the hole until a bolt is installed. There are cutesy plastic plugs for holes that are not used.

Electroless plating is the right, and almost only process able to plate metal inside a hole, electroplating generally do not succeed in plting metal in small deep holes. That said, you have to take in account the added thickness when machining the thread.

If you are worried about the bolt not fitting after plating there are taps that are made .005" oversize for this purpose. Check with your tooling distributor, I'm sure they can help.

When I had a chess set anodized, the plater told me to tap a hole in the bottom of each piece, to provide a mount and contact for the process. The hole was on the bottom, so it didn't matter.

I don't understand the need for the tapped holes to be plated. They are small, aren't they?

I would use a tapped hole for the mount in this process. If you are concerned about the area around the hole not getting plated, have the mounting screw extend out of the hole.

All you have been told about proper cleaning prior to plating, bath flow and agitation, and proper rinse & drying are important for the best results. Somehow, it will never be perfect when/if you 100% inspect these blind holes from lot to lot or supplier to supplier. The only guaranteed way (when possible) is to drill the hole through (since you are 3/4 of the way through any way) and only tap to the depth required. In 30 years, it is the only sure 100% solution I have found.

If not possible, stay with the most disciplined plating supplier to achieve the best results. Good luck!

Thanks. The tapping is parallel to the 50 mm side. As such, it is only 1/4 of the way through. We also have been advised by our processor to go for through holes. However, the drawings are supplied by our customer. It would be a long process to get the drawings changed by the customer (the through holes may affect the magnetic properties). Thanks any way. I will be using the inputs provided by all of you and update you on the results.

Since a tapped hole and then EN Plating will not allow the bolts to fit anymore, can we drill through an EN plate thickness of say 0.0005" and drill and tap after the EN Process?

Also, what about milling a 1/8" flat section off a round bar ~ 1.5 " diameter that has been EN coated, again 0.0005" thickness. Will that work?

Thank you

You can't, I would just insert some anti-seize in the holes, this should stop the rust....

Thank you for the anti-seize tip. Adding a bolt with anti-seize will likely prevent EN to enter the tapped bore. Perhaps ordinary grease may be equally effective?

Since the tapped bore (4-40) is on the OD or a round bar, I intend to go ahead with the EN coating and then grind off the area where the tap is needed to get access to the steel below. I trust that this will work. Only a small grinding depths is needed.