Surface prep for chrome plating

[Frank Ford]

I'm just finishing up a second batch of those steel horseshoe magnets for the vintage guitar pickups, and I'm wondering about the optimum surface finish I can present to the plater. In a conversation with the plating outfit, I came away without the answer I'd hoped for.

It went like this: "Polish them the way you did in the first batch - it was fine." Then a little while later they said that they were so rust damaged in the flood (the plater is in Nashville) that they really didn't know how they looked when they arrived - they were submerged for weeks. That leaves me still wondering how scratch-free they really need them. My first ones were highly polished, and I'm thinking that I'd rather not go quite that far unless it's reasonable.

Mine had a high reflective shine, which dulled back on heat treatment, of course, before I sent them off.

I'm hoping that, say, a really clean 400 grit belt sanding job would allow them to fill with copper, nickel, or whatever is in the process. . .

[Circlip]

Don't ever remember seeing any of your bits looking rough? The more a plater or painter has to fill a surface to acheive a gloss/glass finish, the more the cost. They are going to polish between the different layers, so do you supply a "Keying" surface for the Copper coating to level?

My Fabs foreman used to say that painting would take care of any marks and scratches, not in powder coating it don't, the better the surface to start with, the better the final finish.

Oil prevents rusting on bare Steel parts, the plater is going to de-grease initially as part of the operation.

Regards Ian.

[speedy]

From Rob the polisher and Max the plater.

Frank, FWIW my mate Rob has polished at his old mans plating shop over the Shore for an age. He tells me that the better polished the surface finish the better the plating. They only ever used nickel/chrome. Copper was only ever used for copper plating only and where the surface was beyond polishing without destruction & needed building up to enable it to be brought to a polished finish.
The other that he told me; most other shops use triple plate; copper, then flash nickel, then chrome - to save on costs as nickel is the expensive component.

[NiftyNev]

The better the preparation the better the finish. As simple as that. Copper, nickel, chrome is the proper way to do it. Never heard of polishing between layers unless a different copper solution was used to build up worn parts. Can't remember if that's cyanide or acid copper though. My brother is the plater and been doing it for thirty years or so.

Nev

[Dr Stan]

Frank,

All of the posters are correct. The analogy I like to use is finishing fine furniture with a clear finish. If the surface of the wood is rough, the clear finish will simply conform to the existing surface resulting in a rough and unacceptable finish.

Consequently the smoother the surface finish of your magnets the more satisfied you will be with the plating. There is another step we used in Dalic brush plating that was etching prior to applying any plating. If your surface finish has any smeared metal the etching will remove this smeared metal leaving you with an extremely uneven surface. My boss discovered this when we had some parts tank plated in which the holes had been "bearingized" which is a high precision process to size a hole and also tends to work harden the surface. However it achieves this by smearing or moving the metal around. When we received the parts from the plating shop the surface finish inside the hole reminded one of a miniature moon scape.

[gwilson]

For your info,aluminum is always plated with copper before any other metal is plated over it. As far as I've ever been able to tell,even a small scratch in your surface will be magnified by the plating,because it will shine out and really be seen. I am not aware of any "filling" with other metals,but it could be possible. I am not a professional plater.

[fredwillis]

My old trick is to hold my finger up to the part and if I can see my fingerprints in the reflection then its good to go to the platers.
Its a quick and dirty test procedure.

[Frank Ford]

Thanks, everybody - that's about what I expected to hear. Jason (the pickup maker) says he sends rougher parts to the plater, but those are generally brass. I'm not surprised they'd want polished stuff from me because it's heat treated to max hardness by the time they get it. So I guess I'm back on the buffer. . .