Polishing Stainless Steel to a Mirror Finish
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A discussion started in 2007 but continuing through 2018August 21, 2009
Q. Hi, I am fabricator/polisher for a new company; being new, there is no experience I can draw on. My boss is happy to supply me with almost anything I find that helps the job and I would like to invite any key tips that any polisher should know. We work almost exclusively with SS, all hand tools, I've found trizact, pneumatic drums, I think I've found most of the right equipment but I can't find enough brain food.
I achieve a good dull, satin, brush finish; I can achieve a confident mirror finish but not close to the finishes you speak of, and it takes me far too long -- and polishing interior angles drives me crazy. Best I've found for this is dyna-brade for taking weld fillets out, then a thin mop. If it's a brushed finish I finish the inch or so where the wheel can't reach by hand with scotch cloth, but it leaves a finer finish than our brush finish. Any pointers in any area will be greatly received. Even if you think surely everyone knows that! Try me; no one will think you are amateur for giving me really basic advice, only me for not knowing it already but I don't mind, I know I have a LOT to learn.richard jowsey
- leeds, UK
November 9, 2011
A. Hi, I don't know if this issue has been resolved, or if there is still any interest in this question. Still;
Eric Brown's answer describes the issue nicely. The cause of the "orange-peel" is usually the result of the lap material being too soft for the substrate being polished.
All polished surfaces appear to have a Beilby layer. Acid etching can remove the layer, but that just exposes the microscratches that are present beneath this layer in almost all polishing processes.
Very hard laps produce scratches, but not orange-peel. Progressing from softer lap materials to harder lap materials (Buehler PoliPad, to TexMet to MicroCloth just as examples) gives a clear indication of the situation. The PoliPad with 1 micron diamond as an abrasive will produce very refined, flat surfaces, with some haze or "sleeks" evident. Following with a very short polishing on the MicroCloth (with lubricant-soap) will remove the haze.
However, extended polishing on the velvet-like MicroCloth will result in orange-peel. I believe the orange-peel is the result of differential hardness domains; areas of agglomerated polishing compound versus soft lap.
Buffing wheels by their nature produce orange-peel as well as localized galling.
- Livermore, California, USA
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November 15, 2011
A. Hi Mr. Laurence,
I am Daniel Ocampo working as a tool maker in past 14 years.
Your issue caught my attention.
Regarding the orange peel like appearance on the stainless steel it only means you over polish the workpiece. It has also correlation with the speed of your polishing machine and grit of material you use in polishing. I will give some points which may resolve your problem. If you are using silicon carbide the sequence must from rougher to finer. Example, use grit 600 then follow by grit 800 and then 1000. To achieve the mirror like finish after the silicon carbide you should follow by the diamond paste. Application of diamond paste same as silicon carbide rougher to finer.
Since you have already polish by silicon carbide you use finer diamond paste. Sequence must be grit 15 mic followed by 8-6 micro and for finishing use grit 1 micro.
Hope this suggestion will help you....
- Saudi Arabia
February 23, 2012 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread
Q. I'm an Italian stainless steel worker.
We manufactured a d-curve piece of furniture 180 cm x 120 cm with a polished stainless steel metal sheet.
After welding it we manually polished the welded parts.
The 2 polished finishes have a different mirror finish tone.
Does anyone have a suggestion to manually finish the piece (mirror finish) with a uniform/constant finish?
- Salerno, Italy
March 23, 2012
Q. I have a question about how to specify the mirror finish on stainless steel. We are a manufacturer of cameras and use stainless steel mirrors as part of the optical path so we need a true optical mirror finish with almost no scratches. The mirrors are typically 1 inch diameter 304 stainless. Currently, the surface finish specification for our stainless steel mirrors is "FLAT TO 2 WAVELENGTHS W/ 80-50 SCRATCH/DIG, MIRROR FINISH". We have used the same machine shop for years without many problems but recently we have been receiving the mirrors with lots of long small scratches. After measuring the scratches, I believe they are within spec but do not meet our optical quality requirements. Can anyone tell me what surface spec I should be using?Bob Dobson
- Horseheads, New York, USA
April 25, 2012
A. Thought of Electropolishing?Stan Martin
BioMed Eng. - Portland, Oregon, USA
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August 24, 2012
Thank you for this thread, it saved my life! I was ending up with an uneven "granularity" that looked like a cross between brushed stainless and smeared fingerprints. Then I came across this thread and read Laurence's words:
"If you go 90 degrees to the last operation you will be able to see the lines you have not taken out yet."
Laurence, you are my new best friend! That was my whole problem, and now that I'm using the 90 degree technique, I can see where the granularity came from and I can also see that I'm spending all of my free hours sanding! Maybe you're not my best friend after all, ha ha! I took it back down to 80 grit and I'm only at 220 now and the results are fantastic. It's great knowing when I'm done and ready for the next grit! Thanks again!
- Cupertino, California, USA
August 25, 2012 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread
Q. Hi, this is Abhishek Purohit, from Mumbai, India. I want to know how to do mirror finishing on stainless steel sheets. Currently I am using red oxide with nitric acid and water combination. But I am not getting good finish from above combination. Can anyone suggest me any other idea.
Thanks for your help. Can you suggest if the chemicals I am using are the right one?
August 25, 2012
A. Hi Abhishek. As you see, we appended your question to a thread which answers it.
Sorry, I don't understand your description of what you are currently doing, but mirror polishing is a multiple step operation -- never a single step operation. While you must use extremely fine abrasive in the final step, it would take you more than a lifetime to polish a rough surface with an extremely fine abrasive; and even then, it would cause waviness, orange peel, and selective hardness -- so you must progress through the steps from coarse through fine. Lawrence describes how to do it in 6 steps. Good luck.
Ted Mooney, P.E.
Pine Beach, New Jersey
Stainless Steel 316 polishing from 250 RMS to Mirror finish, what are the process steps?September 6, 2014 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread
Q. I have components with complicated but open surfaces that are Investment cast. I need to bring the 316 material from a 250 RMS finish to a mirror finish.
I want to do some preliminary test to see what finish can be achieved.
Surface are is about 25 inch^2 each.
Owner - Lake Charles, Louisiana
September 19, 2014
I'm not really an expert in surface finishes, but something along the lines of tumbling followed by electropolishing may be what you need.
Stellar Solutions, Inc.
September 22, 2014
A. I question your 250 RMS . I've never seen anything that rough. Normal mill steel comes in at about 35 RMS. So if that is the case, you can burnish or polish for a bright finish; but if you need a smoother finish less than 24 RMS, you do need to use a couple of ceramic steps. Do you know what you are trying to achieve?
September 24, 2014
Thanks for the response, I did a check and used fiber wheels and seems to be doing the job. The finish now is about 25 RMS which is good enough for the application.
Many thanks to all.
- lake Charles, Louisiana
March 27, 2018
Q. How important is the hardness in achieving a mirror finish?
Can I get similar results with 301 1/4 hard vs 301 full hard?
I've been asked to make some stainless steel mirrors as a side project at work. Yes I know we could just buy them...but i have time and materials and would like to be more proficient at it. I polished one for myself years ago but am having a hard time getting the same results. Currently material type is the variable.
I had previously used commercial Brasso [linked by editor to product info at Amazon] and was happy with the result. Now using similar product and process but getting a cloudy finish.
Aircraft Structures - Halifax, Nova Scotia, Canada
March 27, 2018
A. You are talking about 2 different things. Hardness and a mirror finish which is subject to interpretation. Are you looking for a reflective finish or a mirror finish? A true mirror finish requires a smooth surface. A reflective finish does not. To achieve the latter, hardness will effect the time it takes to achieve a smooth enough surface to get a polished appearance, meaning it is more difficult to remove or modify the surface material profile.
March 28, 2018
Q. Thanks for the quick response!
I think 'reflective' would be the best description. Obviously the clearer the image the better. It will be used to make out faded part numbers written inside the aircraft and similar detail work.
When I get back to work I will try to upload a picture of the piece I have next to the piece I am trying to recreate.
The reason I'm asking about hardness is the material I have available is 301 SS and available in 1/4, half and full hard. Just wondering what my starting point should be or what difference there is. It seems both could be equal quality. The full hard will take longer but be more durable and scratch resistant.
- Halifax, Nova Scotia, Canada
March 30, 2018
Q. The piece on the left I polished 7 years ago and am trying to recreate … a little scuffed up but still very clear image within a few feet. The piece on the right is what I'm currently working on.
I think my problem is too much pressure and speed. Is there a better compound to use other than the Brasso in the gold bottle? Thanks.Tony Murphy [returning]
- Halifax, Nova Scotia, Canada
How to get a good polish on a stainless weldmentOctober 17, 2018
Q. We make furniture products, and a couple years ago we started offering polished stainless products. The quality of our polished products has improved immensely over the years, but we can't seem to nail down the final polish that gives it a good mirror quality. Currently, the products look very good from a distance, or in dim lighting, but under sunlight, you still see a grain and haziness in the finish, which is unacceptable to my picky customers.
Our current process is to run the raw material through a Timesaver wide belt sander using 3M Trizact belts, starting at 120 grit going up to A6 (approximately 4,000 grit), we then cut the tubing, use a handheld drum sander to work out any scratches from handling the parts (again going up to A6 grit), then weld them together to the specified shape. The welds are then ground down, then the affected area re-worked with the handheld drum sander. Then we use a felt disc on a variable speed grinder and use white and green buffing compounds, then we use an orange NuVite polishing paste to put the final shine on the product. Like I said, it looks very good in general, but under close inspection looks sloppy.
From what I understand, conventional buffing would be faster and produce a much better finish. But I'm unsure of how we could polish the weldment using buffing pads on a handheld tool.
So I'm looking for advice on the best practice to achieve a better finish considering the process/shape of what we're making, and I'm also looking for advice on what would be the best equipment to use to achieve this.
Shop owner - Wauconda, Illinois, USA
December 8, 2018
A. You may still have to handwork the welds; however, check into electro polishing for your final treatment.
Streaky finish on my SS304 mirror polished part after buffingDecember 11, 2018
Q. Hi. We have a part that needs to be 8K mirror polished on one side. The part is 1170 mm x 110 mm x 6 mm SS304. We bought a single sided 8k mirror polished board. However after we weld some parts to it and it gets moved around, it has some small scratches; small cosmetic scratches. After buffing it with a loose cotton buff and or an orbital wool buffing disc with a fine green wax, the Board has waxy streaks/reflections on it. looks like oil residue not really an orange peal as others have described on this site. I have also cleaned the cotton buffing wheel of wax (using a sharp edge) and tried to dry buff the waxy streaks out, but still no luck.
Any input is greatly appreciated.
Small business owner - Fort Pierce, Florida, USA
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