polishing stainless steel sheet to mirror finish

[Mark Pearse]

Hi everyone

 

My current build is a half model & I plan to mount it on a sheet of mirror finish SS. I have a piece cut to size, it's 750 x 300mm, as per the poor quality photo below.

 

The finish is some sort of mill finish, it's not brushed & it's smooth & relatively flawless but not polished. I want to polish to mirror finish, using straightforward tools like my hands, a drill etc. Has anyone any advice on a simple way to do this?

 

thank you

 

[Jaager]

I did my usual process of imagining a theoretical way to approach your problem:  bars of polishing compound with a gradation of every finer grit - attaching pieces of leather or shammy leather to a disc - maybe using the DIY hook and loop as a way to attach, go at it with a rotary tool.  -AND - I decided that I would probably skip all of that work and go to a glass shop and have them cut me a piece of mirror to the size that I needed.  Glass should stand up to time better than SS.

[kurtvd19]

A front surface mirror eliminates the gap that one sees between the half hull and the mirror's reflective surface that in a std mirror is on the back side.  The front surface mirror is fragile and easilly scratched but once you see the difference the care is worth it.  Front surface mirrors are expensive but a good source is scrapped copy machines - there are places that take these machines apart and sell the parts - mostly in major cities.

[Roger Pellett]

Try successfully finer grits of polishing compounds applied to a motor driven rag wheel.  If you’re not familiar with them they come in sticks that are held against the spinning wheel to load it up. You will need a new wheel each time that you change grits.

 

Your shop must be free of any carbon steel filings shavings etc. that can contaminate the wheel or the part that you’re polishing.  These will leave rust booms on your polished surface.

 

Stainless steel isn’t really stainless. A cleaned surface will form a microscopically thin corrosion film that prevents further corrosion. This corrosion film is what gives it its characteristic grey color.  Once polished, you would have to provide some sort of coating to prevent this film from forming

 

There is also a process called electropolishing that is sort of the reverse of electroplating.  That’s all that I remember from my stainless steel  pipe fabrication days. You’ll have to look up the process.

 

Roger

 

 

[Mark Pearse]

Jaager, Kurt, Roger - thank you for your thoughts. 

 

I'm not going to use glass because of that visual gap from the glass thickness when seen at acute angles, as Kurt noted. The front surface mirror is not something I've heard of & would bear investigation - except that am now the proud owner of a 1.6mm stainless steel sheet cut to size. 

 

Roger, I had wondered if something like this could work. Fortunately my brother has one of the rag wheels mounted to a heavy drill press. The polish acrylic mainly so I'd need to investigate the appropriate polishing bars, but probably a firm that sells them would advise.

 

Any thoughts on the process below?

Gently hand rub with some black scotch brite, then to white (maybe there's one between...), would get me close. Then perhaps the rag wheel trick.

 

thanks

 

[Bob Cleek]

Been there, done that, got the tee shirt.

 

Do not use a buffing wheel chucked into a drill press! Odds are the drill press chuck is held in the quill with a Morse taper which is not designed for side loading. If the wheel is used with any significant pressure, which you will need, the Morse taper will probably come loose (unless it's rusted solid) and cause the chuck to drop out of the quill and possibly cause serious injury to the operator. (Din't ask me how I know this! )

 

Use a six inch or larger solid tightly spiral-sewn cotton or felt buffing wheel mounted on a proper horizontal shaft. Use emory compound (usually black or dark grey) or Tripoli (usually reddish brown) for aggressive buffing. There is also a compound made specifically for stainless, which is fine, as well. When done with the basic buffing, switch to a canton buffing wheel, which is made of a stack of cotton that is loosely sewn, or not sewn at all, and use white rouge compound. (Never use anything but white rouge on the wheel you use for final buffing.)  It will take a long time to bring the shine up. If your buffing wheel gets too full of polishing compound, it can be renewed by gently applying the toothed edge of a hacksaw blade to the wheel's edge to scrape off old compound. Make sure the saw blade is held in a saw frame so it cannot cut you if it catches on the wheel.) Work on one small area at a time until it's done. (If you go all over the sheet, you'll give up long before the whole sheet comes up to a good shine. When it's all shined, wax the sheet with a quality non-yellowing wax. 

 

When working with metal sheet on the buffing wheel, wear leather gloves and exercise extreme caution never to present the edge of the metal plate to the wheel in such a way that the edge of the plate can be caught by when wheel and be knocked out of your hands. Serious injury can result. Always be aware of the wheel's direction of spin when presenting the piece to the lower edge of the wheel when it is spinning downward to be sure the edge will not catch on the wheel. A face mask is a must, and a shop smock is handy, because this is a dirty job.

 

Again, it will take a long time, but you eventually will have a stainless plate with a mirror finish. This is not a job to attempt doing by hand or even with a Dremel tool.  Stainless is hard stuff.

 

Here's a good video how-to-do-it. The safety instructions are very good. Don't underestimate a buffing wheel. It can be a dangerous machine.

 

 

 

Edited May 17, 2021 by Bob Cleek

[Mark Pearse]

thank you Bob,

 

I'll digest that before attempting anything

[shipman]

I have a 1956 BSA motorcycle. 30 years ago I replaced 99% of the fasteners, laboriously hand polishing each one, using files, emery and finally using a buffing wheel. That took me an entire winter but the results were exceptional. After all the years, being exposed to oil, road dirt and British weather, a quick wipe with an oily rag reveals all the glitter. Brilliant!

If I'd gone with new cadmium plated steel it would be rust and need replacing again.

[Mark Pearse]

Hi Shipman, thanks & sounds like a lovely motorbike. What compound, if any, did you use on the buffing wheel?

[shipman]

Mark, after all these years the source of the compound eludes me, however I do recall it was red 🙄

 

 

 

[shipman]

OOPS! Don't know what happened there......Admin, please remove the duplicates 🤓

[mtaylor]

13 hours ago, shipman said:

OOPS! Don't know what happened there......Admin, please remove the duplicates 🤓

Done.

[druxey]

Red? Sounds like Tripoli compound. Sweet bike, BTW!

[wefalck]

Check out jewellers' or lapidary supply stores. They have all grades of grinding and polishing pastes and sticks, as well as buffing wheels.

 

Tripel or Tripolis (as it seems to be called in the USA) is a fine clay that came originally from Africa and is usually sold as sticks bound in wax.

 

Rouge or Paris Red is iron oxide finely ground and is sold in sticks bound with wax to be applied to buffing wheels, as compacted poweder in tins (like the ladies' rouge), or as cream in tubes (as polish for silver and brass).

 

Vienna chalk is usually sold as compacted blocks for rubbing, but may also be the active component in creams

 

Tin oxide is sold as powder and is used with a drop of oil on a glass or hard steel plate to give a mirror finish to watch components

 

Grinding and polishing is the progressive removal and flattening out of surface roughness. At each step a homogenous surface has to be achieved, deep scratches left in a previous step will not go away in the following step.

 

It is important to always move in one direction, cross or circular strokes lead to irregular patterns that will not result in a mirror finish on larger surfaces.

[shipman]

It's also worth noting there are many grades of S/S, some I've encountered are so hard right through and impossible to improve the milled finish. Most nuts and bolts seem to have a hard skin microns thick, once that has been removed the softer under surface takes a lovely polish rapidly.

Avoid S/S plate which has a grey rolled grain surface....it can be levelled and polished but the effort isn't worth the effort.

May I suggest getting a supplier to provide the type which already has a mirror finish, but cut to the size you require. This usually comes in plate 1-2mm thick. Be careful not to scratch it  as removing that is a nightmare.

[wefalck]

OK, he doesn't want to throw out his nice piece of SS, but there would be other option, such mirror-coated Plexiglas (which even allows you to drill holes from the back to mount the half-model).

 

Just before reading this thread, I happened to see a Chinese vendor on ebay, who sells 304 SS with a mirror finish already ...

[shipman]

If you have a local chrome plater....for a modest fee he will polish your plate for you 😉

[jefferyt]

7 hours ago, shipman said:

It's also worth noting there are many grades of S/S, some I've encountered are so hard right through and impossible to improve the milled finish. Most nuts and bolts seem to have a hard skin microns thick, once that has been removed the softer under surface takes a lovely polish rapidly.

Avoid S/S plate which has a grey rolled grain surface....it can be levelled and polished but the effort isn't worth the effort.

May I suggest getting a supplier to provide the type which already has a mirror finish, but cut to the size you require. This usually comes in plate 1-2mm thick. Be careful not to scratch it  as removing that is a nightmare.

Some Metal shop stock a bright Annealed type 430 S/S  in a #8 mirror finish. It should be available in sheet form from 0.020" to 0.062" (0.9 mm to 1.6 mm). Look for metal shops that specialize in restaurant and hotel equipment. Metal Supermarket may carry it as well if there's one in your area. 

[Mark Pearse]

thank you everyone

 

That is a big help. I'll experiment on a corner of the sheet soon & see how it goes.

[Mark Pearse]

The ideas here helped a lot & I am happy with the results. Most of the tools I used are below: some mesh sanding sheets 400,600, 800 grit; a sponge pad used in a drill, Autosal metal polish. I actually did borrow a fabric polishing head & green Tripoli wax, & it helped as well but didn't seem to do as much as the Autosol & sponge pad...but perhaps I needed to do both. You can see the reflection is  clear, but not a full mirror finish. It took a couple of hours of hand sanding using the sanding sheets, with a light spray lubricant at the same time, about an hour with the fabric head, & about 30 minutes with the sponge head.

 

 There is a slight ghosting in the reflections, but I am very pleased with that. It adds of softness to the reflection that is very appealing, & was quite unexpected. You can see the effect in the reflection below.

 

 

It's likely that I could have gotten closer to a full mirror finish, but I think the result that I got is what I prefer.

Edited June 17, 2021 by Mark Pearse

[lmagna]

Congratulations on a very nice finish. I agree, the slightly rustic uneven shine looks much better than a true modern day mirror.

 

If you do it again, you may look at toothpaste. It is surprisingly abrasive in most cases.

Edited June 17, 2021 by lmagna