Clearance for chroming

I have two pieces that will eventually be chromed. One will be held
via a shoulder bolt and the other will have pressed in bushings.
Neither piece spins. they must rock back and forth at low speed and
very light load. Should I allow for chroming when I ream the holes or
ream them afterward. If afterward - how much material should I leave
or should I ream them to size and then ream them again after chroming.
Thanks
Jim
Reply to
Jim
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You didn't specify if your chrome was ornamental or hard chrome, so I'll assume you mean ornamental. If you request it, they can mask off the area of concern so it doesn't receive any plating. I am of the opinion that would be in your best interest. Once you get parts chromed, you risk damaging them in handling if you do any kind of operation on the machines. Further, if you screw up and scrap them, you're out the chroming costs along with the loss of the part.
If, by chance, you find that you still want to ream your holes after plating, anything from a couple thou up to no more than .015" should be enough, depending on the condition of the hole you've created. Reaming any more than .015" can get testy, especially in small holes. I suggest you double drill your holes so the end result is cleaner and more likely to be the size you want. Start with a drill that is a couple sizes smaller for the first drilling.
Hard chroming would not leave you any options, you could not do the work afterwards unless you have access to grinding equipment. Chrome (hard chrome) can not be machined. You would have to mask finished diameters.
Harold
Reply to
Harold & Susan Vordos
It will be very difficult (nearly impossible) to allow for chroming thickness on anything that requires a few thousandths precision. The processes used for the plating and prep are just not controlled that well. A plated part can easily end up several thou over or under the pre-plated dimension. I speak from some very bad expriences with bearing surfaces in chromed motorcycle wheels. It will be best to work with your plater ahead of time when designing the parts to see if he can mask off the critical surfaces. And, if he agrees that he can mask the critical surfaces make sure this ends up clearly on the work order. On aluminum in particular it is possible to end up undersize because of an acid etching step during prep. Otherwise you'll need to plan on grinding to the final dimensions after plating.
Reply to
Terry Mayhugh
Is this hard chrome, or bright chrome ?
Chrome is of negligible thickness (this is a rec.* newsgroup). It's so thin that it's a problem to measure it. If you're making any allowances, it's more likely to be an excess of material, to account for the losses in polishing (or reaming).
Chrome plate is about 0.0002 to 0.0005 (half a thou) for bright or most hard chrome. Hard chrome _can_ be thicker, up to about 0.015 maximum, but this is a specialist process only used for recovering worn out components, or for some extra-hard-wearing coatings. Few platers do it. As to the precise thickness you're going to get, talk to your plater.
Because chrome is so thin, it's usual for all surface polishing to be done before chrome plating. If you're putting chrome over nickel plating (which is common practice), then the nickel will be considerably thicker. I don't know about reaming, but it's usual to polish, nickel plate, final polish, then chrome.
-- Smert' spamionam
Reply to
Andy Dingley
Also there will be a slightly higher ridge of chrome build up right next to the masking. You could machine that area down a few thou beforehand over a length of about 1/8". HTH
Reply to
John

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