Polishing stainless steel...

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Zach
Boat Obsession Medal Finalist
Posts: 684
Joined: Wed Jan 25, 2006 6:28 pm
Location: Beaufort, North Carolina
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Polishing stainless steel...

Post by Zach »

Wrote this for another venue, thought somebody here might find it useful...

So one of the things I have to do quite often, is polish stainless steel. 316 will still tarnish if it was ground on by a disc that touched mild steel in its life... The mill scale and carbon present on the surface allows for the same rusty grunge to form.

So, for the look of a yacht and the corrosion resistance it needs to be polished.

What I do is take a polishing sander (Makita 9227, which is my chosen favorite grinder for doing fiberglass work...) and put on a hard foam pad that takes pressure sensitive adhesive sandpaper.

In my case I grab a box of 80, a box of 220, and a box of 320 and get set up in a comfortable working position. The 80 gets walked down the piece, with a comfortable feed rate... meaning that whatever speed you move the sander you keep moving at that same rate forever and always. Inches a minute, feet a minute... whatever works. Just never stop in one spot, if you have pits you have to burn down the whole length till they are gone or you'll dig a low spot that doesn't look very good.

When you get the end your scratch marks should be regular and equally spaced. Go back down the part until all the pits are gone, they show up as dark specs that hold metal dust.

Once everything is flat and pit free, switch over to 220 and walk it down the part. You can now lean on the sander a bit, which is where having an adjustable speed works nicely. PSA sandpaper discs overheat the adhesive if you stay in one spot with a lot of pressure... So focus on moving steadily.

Now flip the part over, your half moons (Random orbitals on steel are overkill...) formed by your sanders rotation will be taken out or evened out by changing the direction you move the sander. Curved scratches are the hardest to hide, where as straight ones disappear...

Step it up to 320, around now you'll see the outline of yourself in the part. You are now shooting for an even luster. Like... brushed stainless.

After you are pit free, flat, and smooth...

Grab a 4.5 inch angle grinder, take off the disc and load a 5 inch spiral stitched buffing wheel on to the grinder. Tighten up as tight as you can get it. Grab a few tubes of polishing compound, cut the cardboard so you have a rounded corner knocked down a little less than a 45 (Think fish-mouthing one side of a pipe...) Touch the grinder to it to load the wheel, and work it down the part.

You'll hold the grinder perpendicular to the works surface. Flat plate on a bench, the grinder is on its side. Perpendicular the length of a pipe... but being dragged up and down it.

You have in your hands a polishing wheel spinning greater than 10,000 rpm. There is a right way and a wrong way to hold it, both hands... and let it catch an edge, very quickly you'll see with one side up it catches and tries to run away, on the other side it digs in and makes you work.

As you might guess, it takes a little less time to polish something at 10,000 rpm, than on a buffing wheel that is bench mounted spinning 1750rpm. I use a hitachi 4.5, its the lightest weight and smallest overall height. G12SR3... side mounted switch, paddles get in the way on intricate parts as sometimes you can't get your fingers on them, and the switch has to bump something to get around the corner...

So, when your wheel is about done, don't use it all the way up... set it aside for when you need to get into a tight corner.

Avoid loading a finer grit on top of a coarser one. I start with grey light cut compound and finish up with red rouge. You end up with a mirror, and don't have to go any farther than 320 grit.
1961 Pearson Triton
http://pylasteki.blogspot.com/
1942 Coast Guard Cutter - Rebuild
http://83footernoel.blogspot.com/
One Way David
Skilled Systems Installer
Posts: 183
Joined: Sat Aug 02, 2008 8:46 pm
Boat Type: Pearson Ensign
Location: Kansas

Re: Polishing stainless steel...

Post by One Way David »

Thats a good guide Zach, thanks for the post. And one could use that technique for any steel. I've made some HSS knives and tools that way.
Never finish all your projects or you'll be bored.
boatsnh
Rough Carpentry Apprentice
Posts: 61
Joined: Mon Feb 02, 2009 6:55 pm
Boat Name: IRIS
Boat Type: Dickerson 36 Ketch
Location: Concord, NH

Re: Polishing stainless steel...

Post by boatsnh »

Hi Zach,
Have you ever taken some of the stainless you have polished & had it then "Electro polished"? I bumped into this process when I was contemplating having a custom steering station bracket made and the folks at Edson in New Bedford Ma. mentioned that I ought to take any custom part out and have it electro-polished. So in the spirit of the project I talked to a local electro polishing shop. Not that expensive & the benefits seemed enought to justify a reasonable $ outlay. The process removes any surface contamination & Actually removes material and makes the surface more "microscopically" smooth - no little places for the stainless to corrode. It greatly minimizes any future discoloration &/or stainless bleeding. The new steering station guards from Edson are all electro polished & they look nice - My 11/4 tube guard looks as good as the day it went in 3 seasons ago. Oh...the custom part I was going to fabricate?? Edson had an aluminum part that was made for an oddball application & it fit perfectly after a but of work on a drill press with a 1 1/4 inch bit. Only issue is it's painted white & not shiny stainless. Such is life....
Edson has some good folks in their office willing to offer lot's of help. They are at the Maine Boatbuilding show every year and worth a visit.
Mike
Zach
Boat Obsession Medal Finalist
Posts: 684
Joined: Wed Jan 25, 2006 6:28 pm
Location: Beaufort, North Carolina
Contact:

Re: Polishing stainless steel...

Post by Zach »

Mike,

I've never had a need to have anything passified, but if it's going to see salt water it is a good idea. I started out polishing tool and die equipment, which just gets oiled down... Grin.

Only real tip hidden in there for anyone that has done any polishing, is using an angle grinder!

Cheers,

Zach
1961 Pearson Triton
http://pylasteki.blogspot.com/
1942 Coast Guard Cutter - Rebuild
http://83footernoel.blogspot.com/
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