I've had lots of fun doing plating with copper, but I've never tried it
with real machine parts.  It might prove useful for some applications
in the restoration of mechanical music instruments.

I use a solution of battery acid (from the auto parts store, four bucks)
copper sulfate (from the garden store) and water (from the faucet) in
whatever proportions seem reasonable (maybe 50-50 acid/water, added to
which are enough blue copper sulfate crystals to seem like too much;
it'll all dissolve overnight.)

Fold one inch of a six-inch-long piece of #12 copper wire sharply back
on itself and pry it apart such that a quarter can be inserted into
the crook and stay there.  Stick the quarter plus another piece of the
same wire into a flask containing the poisonous blue solution, and apply
current.  A few volts -- maybe three volts -- will do; twelve volts
gives you a brown glob of infinitesimally-divided pure copper powder on
your quarter, which impresses no one.  Takes about one second to make a
nice shiny copper finish on the coin.  The negative side of the source
goes on the coin.

The reason I mention this, and I'm aware that it has little to do
with the topic at hand, is that to the vast majority of the public,
electroplating is magic.  And I mean it: they've never heard of such
a thing!

I do the demonstration about every week at our big science museum, and
for some reason it's an utter show-stopper; you'd think I'd spun straw
into gold.  For power, I have a silly hand-cranked generator I made
from a small DC motor friction-driven from a lawnmower wheel.  I have
a little kid do the cranking.

Of course, you have to turn the crank the right direction, but once
you get a little bit of copper on the coin, you can then crank the
generator backwards to remove it.  That _really_ does it for the
assembled crowd!

A USA nickel coin is about the toughest thing to plate; there's
something about the cupro-nickel alloy that is uncooperative.  The
easiest is a plain steel nail: just dip it into the solution and it'll
self-plate instantly; the acid plus the steel form their own battery.

Whatever you plate, the part must be thoroughly cleaned of acid residue
when you're done or it'll corrode in ways you've never imagined.

Mark Kinsler
Lancaster, Ohio, USA
http://www.mkinsler.com/