I'm working on a project to restore a few small watch parts that need
be polished for further treatments. As the surface is uneven, it is
difficult to polish some surfaces and I trust EC Polishing to be my
However, I don't have the composition of the bath (for a simple home
setup) and other process parameters.
I would appreciate any tips and experiences on this topic.
Go ask a horology newsgroup. We're hairy-arsed engineers round here and
our processes are crude and unsuitable for polite company.
For anodic cleaning and electropolishing dirty brass I've used the
following. I _think_ it's based on Canning's Anodax cleaner formulation,
but I've no idea how accurately.
1 part caustic soda (sodium hydroxide), 7 parts washing soda (sodium
carbonate). Mix to a strength of 8oz / gallon. Use near-boiling hot
(90°C) at a current around 30A/sq ft. and agitate it by bubbling air or
CO2 through the bath. Max duration about 30 seconds.
For electropolishing you probably want to tone it down a bit and do it
Wash afterwards, swill in hydrochloric acid pickle, then wash again.
I don't recommend this process on smallparts without experimentation.
But it's cheap to make up, easy to work with, and might give you a
Big problem is that electropolishing doesn't like to penetrate down
holes, and is very good at rounding off sharp edges like you probably
have at the edge of your slot. You don't get significant polishing past
about 10-20% of the diameter down a hole, and deeper than that (down to
maybe 50% of the diameter) you can actually roughen and degrade the
surface as the current density falls off below what gives good
polishing. Don't know where you live but most any big city will have a
few electroplating/electropolishing shops. Take your part for a visit
and let a pro look at it in person.
Carl Ijames carl.ijames at verizon.net
The hole problem can be addressed by placing "robbers" (conducting
wires) through them. This is what chrome plating shops do for the exact
same problem. Also, it helps to have the solution in motion via a pump.
Rounding is a function of time left in. If you over-polish, you round
the edge. Can't change the physics of that!
Thanks for answering.
If I go to a shop they will laugh at me...
The reason is that my parts (watch screws) are so tiny, about 1mm
I would try electroless chemical polishing at home (I don't have more
that 6 at a time) but I don't know the composition of the acid bath.
Can you please help?
Sorry, can't help with electoless polishing. What makes you think a
shop hasn't seen lots of stuff like your screws already? If you are
lucky they will relish the challenge :-).
Carl Ijames carl.ijames at verizon.net
I get a lot of stainless electropolished commercially- they use a
propietary solution, but the main ingredient is phosphoric acid. My
guess is Ospho would probably work, or dilute phosphoric, which is used
as a paint prep, and is often available at good paint stores.
For stainless, there is a citric-acid based product line called
"Citrisurf". They offer cleaning, passivating, and polishing formulas
and equipment. I wanted a small amount to do some electrocleaning and
passivating of stainless for jewelry -- after some discussions with the
company and a look at their MSDS, i decided to do some experimenting on
my own. For the record, the company was very helpful and even offered
to send me a few samples of their products, but the minimum purchase
quantities are way more than I could ever use.
Anyway, I got good results on 416 stainless with a home-brew mixture of
10% food-grade citric acid, and 1% disodium EDTA, dissolved in
distilled water and run at about 90 celsius. I was using a home-made
brush plating setup (with reverse polarity, of course) at about 18
volts, and the "wand" was a piece of flattened copper tubing with a
strip of fine scotch-brite wrapped over it and secured with a wire tie.
I got very good results with electrocleaning, being able to easily
remove the brown heat-stain from prior silver-soldering. After final
polishing, I then passivated the pieces with a 20-minute soak in the
Cleaning and passivation seemed to work well -- I also noticed a
reasonable amount of polishing action during the cleaning, though that
was not my principal objective.
In this formula, the sodium EDTA serves as a chelating agent to hold
dissolved metal in solution.