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

"Jim" wrote in message
m...
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

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

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.


"Jim" wrote in message
m...
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

On 7 Jan 2004 09:53:52 -0800, (Jim) wrote:

I have two pieces that will eventually be chromed.

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

Harold & Susan Vordos wrote:
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.

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
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