Polishing Of Ss

[Paul Seamons]

I have occasion to have various SS fittings, bases etc. fabricated at my local machine shop. These are fine and functional but with a "mill finish". Anyone have any experience polishing SS from the mill finish I get at my shop to the nice, almost mirror, finish found on most marine hardware?

[Renoir]

The "easiest" method is to use a right angle air tool and 3-M Rollok (sp?) sanding discs then moving to the 3-M abrasive pads and then buffing wheels.

For welds start with 36 grit discs then 60, and 80. Practice your method of using the outer diameters of the discs so as to not cause unwanted damage to areas adjacent to the welds. Move then through the coarse, medium, and then fine abrasive pads. The 2 inch diameter pads work best on tight places and work everywhere else also. Use the abrasive pads to work through removing the marks left by the bending dies used to form your piece.

Buffing takes a lot of horsepower. Use the black sticks for compound designed for stainless. Use 3-M (there are a few other brands as well) fiber wheels (they look like a plastic version of wire wheels and cups) which are impregnated with a fine abrasive, to get inside the welds that you cannot dress down with the fiber pads if the welds have not been left "proud" of the adjacent virgin stainless. This removes mostly the coloration left by the welding process which needs passivation to keep from showing rust and discoloration. A better method of "electrocleaning" without having to use nasty combinations of Nitric acid is to use a 25-30 Volt power supply current limited to about 1 Amp. Attach the negative lead of the supply to a sponge soaked with Oxalic acid (a common benign acid found in Rhubarb, for example, and most easily obtained as FSR...Fiberglass Stain Remover in boat stores). Attach the positive lead to the stainless. Slowly work the gel-impregnated sponge around the welds and watch the discoloration dissappear. This works well for cleaning rust off of stainless. Grease and oil will interfere with this process.

If you allow too much heat buildup to occur when dwelling with a buffer wheel on the part you will discolor the stainless and need to either electroclean it with the power supply or use an abrasive pad again before buffing again.

[Brion Toss]

Renoir,
Nice post!
Fair leads,
Brion Toss

[tpg]

Off topic, I know. Can't figure how to post new topic. Is there a link I'm missing?

My question is; what is the best equip for mast climbing - assuming the climber is 60-years on
& may be climbing without aid of other hominids.

Qualify that, please, to under $500 bucks...make that $300 bucks). Mast height circa 50 ft.

And, Why has El Jeffe, "The Brion," not launched his own mast climber?

Highest regards. tpg

[Paul Seamons]

Thanks for your complete description, Renoir. That should get me started.

[TomP]

Paul,

A good source for both the tools and materials as well as a wealth of knowledge in their forum is available at http://www.caswellplating.com/buffs/buffman.htm

They seem to carry those odd shaped cones and pads that make polishing that much easier.

Oh, and regards to Renoir. He is right on with his technique though I think 1 amp at 25 volts is a little high. We use 12VDC and the amperage is based on the surface area in the bath, rough .1A per 1 inch of surface area for a .00005 coverage. Oxalic acid would not be my choice. It is not agressive enough. I would use a 33% solution of nitric acid. A little more agressive.

The passivation method we use, and refers to ASTM A380 treatise are:
Grades with at least 16% Chromium (except free machining grades e.g. 303)
20-50% nitric acid
Room temp. to 40?C
30-60 minutes

Grades with less than 16% Chromium (except free machining grades e.g. 416)
20-50% nitric acid
Room temp. to 40?C
60 minutes

Free machining grades such as 303, 416 and 430F
20-50% nitric acid + 2-6% sodium dichromate
Room temp. to 50?C
25-40 minutes
We keep our acid tank at about 38C. Any hotter and emissions become a problem.

Electropolishing is by far more favored and much much less labor intensive. But it has its own set of issues. Namley that you can turn your garage into an EPA Super Fund site if you are not extraordinarily careful. Here is the flow chart we use for this process:
Heavy Alkaline soak and clean (Ph 10) we use caustic soda ash. Garunteed clean
Cold Water Rinse
Acid (Sulfuric) descale
Cold Water Rinse
Electro polish
Drag out (looses the heavy metals)
Polish rinse
Nitric Acid bath
Cold Water Rinse
Hot Water Rinse
Cheesecloth wipe and buff.

It is theoreticaly possible to set this kind of operation in your garage, but by the time you have everything needed to start: heaters, tanks, FUME HOOD AND AIR SCRUBBER, and the power rectifier (which, for a small one can run close to $1000), chemistry supplies, and lots of beverages for your neighbors when they complain about the smell. Might just be easier to find a local polisher.

Hope this helps.

Originally Posted by Paul Seamons

I have occasion to have various SS fittings, bases etc. fabricated at my local machine shop. These are fine and functional but with a "mill finish". Anyone have any experience polishing SS from the mill finish I get at my shop to the nice, almost mirror, finish found on most marine hardware?

[Renoir]

TomP's input is wonderfully "industrial" yet, as he states, can certainly be performed at home in the garage. Here is a comment regarding the convenience of using a voltage higher than 12V and a current limit higher than one used with nitric acid.

Resistivity of the electrocleaning (I like to call it electrocleaning rather than the presumptuous electropolishishing term which tends to connote something that might compete with actual mechanical polishing which it does not) decreases with increased pH of the solution used. The greater the pH the more dangerous it is to use and the more difficult it is to obtain for us in garage-type operations. Nitric acid keeps best in glass containers which are VERY dangerous to have in an unsecured area accessible by children or unwary adults.

So, if you want to use easily obtained solutions, like lemon juice or FSR without being too concerned about getting ANY of it in your eye on your skin you need higher voltage and higher current to overcome the greatly increased resistivity of a sponge soaked with the milder pH solution while making it easy to use. You can get a tingle from using 25V if you happen to get yourself across the voltage with acidic solutioned hands and, therefore, you chould use plastic gloves (like nitrile or vinyl or).