Mirror polishing stainless sheet - to perfection

[samfish]

Hi guys.
I am aware that you can buy stainless sheet pre-polished, but I have a job where the reflection needs to be absolutely PERFECT!
They have shown me a sample of the finish they need, and it looks like a perfect mirror. From some directions you can still see VERY slight 'pit' marks - I guess this is where more material needs to be removed.
Also the 2x1m (1.5thick) sheet appears to be guillotined, so the edges have very slight distortion....
I have not got any experience polishing stainless, but I have lots of paint polishing experience, and I am sanding/welding metal most days.
I have a few questions, and I would be very grateful for any advice.

Better to laser cut do you think? Can they laser cut mirror polished stainless?

Will the 'paint' polishing compounds and mops work on stainless, or is there something better? I have a decent air powered polisher/mop.

Is it simply a matter of working up through the grades with a decent DA sander, to 2000 then compounds?

How 'perfect' does a 'mirror' polished sheet arrive from suppliers?

Is 316 grade better for polishing than 304?

Any other advice is greatly appreciated.
Thanks
Sam

 

[langy]

I use a lot of pre polished stainless and it's not perfection for sure but it's pretty good, I then just polish it but you need the right gear
You will struggle with a buffer.
Laser won't hurt it but the edge will discolour slightly

 

[samfish]

Thanks Langy.
What gear do you use, if you don't mind me asking?

I have seen alot of information about polishing components on wheels, but what is the ideal set-up for sheet?

I have a big compressor and alot of patience

 

[samfish]

I just spoke to these guys, and he was quite helpful.

So an angle grinder is better for the speed?
A kit like this?

http://www.metalpolishingsupplies.co.uk/pro-max-angle-grinder-6-metal-polishing-kit/

 

[cr500dom]

Laser won't hurt it but the edge will discolour slightly

It depends on what sheilding gas is being used. Laser wont discolour the edge if you cut with Nitrogen shield

 

[langy]

Thanks Langy.
What gear do you use, if you don't mind me asking?

I have seen alot of information about polishing components on wheels, but what is the ideal set-up for sheet?

I have a big compressor and alot of patience

Air powered won't cut the mustard i'm afraid, it will just stall, I use a hand polisher or proper machine, Like below, its not easy and you need to know what your doing.

 

[ronan]

I used to work making up and adapting hose couplings and fitting along with sch 10 pipework , sometimes it had to be polished , we used to send them to a place that did electro-polishing, it leaves a very smooth surface.

 

[AndyStobbs]

Use a compound called autosol for polishing stainless/alu on my motorbike.
Not found anything to better it yet.

 

[langy]

Use a compound called autosol for polishing stainless/alu on my motorbike.
Not found anything to better it yet.

Autosol is the last thing I would use as its abrasive, fine on aluminium but will scratch Stainless & Chrome, the compounds for polishing stainless is far finer.

 

[AndyStobbs]

Have to beg to differ as I've always had good results myself on silencers, both stainless and chrome.
Aluminium is surely softer than stainless, why would it scratch one but not the other?

Not trying to question your methods or findings, more wondering why two people could have such different results.

 

[ford34/2]

Given the choice I would stay well clear of working with Mirror finished Stainless, I have fitted stainless mirrors in high risk vandal areas and also in high risk patient areas, I have worked extensively with Chrome formica, identical to a Mirror,

If the Architect wants a MIRROR type finish use a mirror.There are plenty of Glass options for safety.

Trying to Polish and match a manufacturers finish or to try and better that finish -- forget it. The last "polish cutting Liquid" we bought--was over £50 for a 1/4 litre. But in fairness it was unbelievably brilliant.It was diamond based and did glass as well.It took over a day for a few square inches to get perfect.
You only need to wipe the surface with your handkerchief and its scratched.The bigger the area the worse the problem will be, and it will be like the hall of mirrors when you move past a big area.Images will be distorted.

Stan

 

[hotrodder]

I'm with Langy, autosol is too abrasive for good chrome (or for brightening/cleaning anything that was highly polished) and results in fine scratches. Maybe not properly accurate but it's kinda, sorta like grinding or sanding in that harder materials need a different abrasive for best results... to do with how they break down in use. For polishing metals you need heat to get the compounds (abrasives in grease) working which means enough power to lean on the work without dragging the rpm down. If you can't lean on it without stalling the kit then you don't generate the heat and end up just spreading grease around the work piece

How big are the guillotined pieces and what/how are they attached... flawless shiney is one thing but a perfect, distortion free mirror in 1.5mm thick stainless?

 

[zardoz]

doesent ally have an oxide coating on its surface though. Is that not what you are polishing when you polish ally ?

I know nothing whatsoever about this. So I an going to put myself forward as an expert and reccomend that you try gradually finer grits then a polishing wheel, then a cutting compound and a rag wheel.

 

[hotrodder]

Stainless does too, a crazy thin layer of chromium oxide is what makes it stainless. With ally the oxide layer is porous and tends to grow thicker with time hence it dulling more easily. Heat tint colours from welding stainless is the result of a thickened oxide layer refracting light differently and anodising ally involves artifically growing a thicker but very uniform oxide layer and then sealing it

 

[brightspark]

http://www.englishcustompolishing.com/usca/stainless.html

 

[langy]

Have to beg to differ as I've always had good results myself on silencers, both stainless and chrome.
Aluminium is surely softer than stainless, why would it scratch one but not the other?

Not trying to question your methods or findings, more wondering why two people could have such different results.

Ask any professional polisher and you will get the same answer Andy, If you take a piece of highly polished stainless and use autosol it will leave scratches in it.
Using anything abrasive on chrome is madness, only a cream cleaner should be used.

 

[langy]

doesent all have an oxide coating on its surface though. Is that not what you are polishing when you polish ally ?

I know nothing whatsoever about this. So I an going to put myself forward as an expert and reccomend that you try gradually finer grits then a polishing wheel, then a cutting compound and a rag wheel.

Polishing is the process of removing surface imperfections so that it reflects light rather than absorbs it. The more light it reflects the better it is polished.

When a piece is polished, what we do is to change its surface. We remove surface imperfections by scratching them off with various grits.
We start with a coarse grit and gradually reduce it to finer grits. Each grit has a scratch factor. We work our way from a coarse scratch to one that cannot be seen by the eye. The small particles on the surface become polarized. They line up like soldiers and the surface becomes slightly harder, and more resistant to oxidization, acid and water stains. Water runs off easier, as it is can’t get a grip on the polished surface. It is also more resistant to corrosion, just because of its smoothness and its hardness. Of course it will dull with time due to handling and chemicals in the atmosphere.

Corrosion sets in when the ions no longer line up like soldiers. The surface gets attacked by chemicals in the air and the little soldiers start falling by the wayside one by one.
Once the oxidization starts, if left unattended the polished surface dulls and can discolour.

 

[samfish]

Thanks for all your replies.

The panel is for an artist, and will be supported by a subframe. The idea is the visual clue of it being a mirror, but having the supple qualities of still being a sheet of steel. A glass mirror is always obviously glass.

I am considering getting the 2x1m laser cut from larger sheets, as the gelatine edges are just not clean enough.

I have seen all the specialist pastes/waxes and see those as the solution, but I am interested to hear the best possible machine. Is converting a 6inch angle grinder going to do it?

I have a 'mirror' polished sample from a supplier, and it is very very reflective. But it is still slightly dull, and not good enough. It needs to be super bright and reflective - I know it is possible, as they showed me something from their last supplier (they are changing because other bits where not up to scratch).

I am aware I may be jumping in at the deep end, to obtain perfection...
Although I have alot of experience of sanding aluminium/steel up through the grades to a satin finish - but just not 'perfect mirror'....

 

[langy]

Thanks for all your replies.

Is converting a 6inch angle grinder going to do it?

.

 

[samfish]

Quite a few online retailers seem to sell this kind of stuff: http://www.abrasivesformetal.co.uk/inoxi-grinder.aspx
These look great:
http://www.youtube.com/watch?v=Az9PfQzAL6U

Ok Ok, maybe it is all aimed at the hobby market...

What is the ideal for polishing large stainless sheet? 6 square meters.

I know it isn't going to be a breeze, and I'll ache after. I have done my fair share of 45+ hour-weeks of sanding.

Please, where did you get your large hand polisher from Langy? Or similar?