How was this Mirror finish achieved on stainless?

abdat60 · Jan 1, 2018

How was the finish done on this stainless steel "screw"? It a mirror finish. Im not sure what type of stainless or if is indeed stainless at all. Its pretty heavy, definitely not aluminum, although it does have two aluminum clamps inside of it attached with three bolts. I have seen knife makers like John Grimsmo polish a knife to a mirror finish. Any input?

abdat60 · Jan 1, 2018

As you can see the inside and bottom were not finished with a mirror finish because it is not required as they will have nothing in contact with them so friction is not an issue. To the contrary of the smooth outer side where it will have foam cups sliding on them and minimal friction is required hence the mirror smooth surface.

triumph406 · Jan 1, 2018

i would start with progressively finer grades of wet and dry, finishing with 1000 grade, then either polish with a buffer wheel, or use polishing compound with a rag.

If it was turned then it would be relatively straight forward to get a good polish. A milled finish would take longer. Also if you have to maintain a tight tolerance that will dictate how much material you can remove before polishing starts.

scadvice · Jan 1, 2018

I recall seeing some parts that somewhat hand finised to a resonable point then they were "Electropolished". If my memory serves me correct that was the term used. It's kind of like reverse electroplating. There was final polising afterwards.

LKeithR · Jan 1, 2018

Any place that does chrome plating could easily polish that--much easier than doing it yourself. That "might" be electropolish
but I think it's a bit too bright...

litlerob1 · Jan 1, 2018

Looks Chromed to me. Not to say you can't get there without, but that would be the easy(not necessarily cheap) route. I would try to get a hold of the print to see exactly what material it is. I can tell you it ain't 12L14 or 1018 or A36.

It seems like an obvious Turning job to me, but lately the Mill guys around here seem to think different.

17-4, 304 and 316 finish absolutely beautifully. With a Wiper insert, high SFM and slow Feed I can get a finish pretty damn close to that right off the machine, with those SS's. I have achieved a 4µin. per the Profilometer. :eek:

R

billzweig · Jan 2, 2018

Electro-chemical or chemical polishing leave a shiny finish but not precise surface. It is mostly used for decorative, food industry, high vacuum, high voltage - for parts that need polished surface but not perfect mechanical or optical accuracy. Buffing will have a similar effect. If both accuracy and finish are needed, it can be done by fine machining or grinding and then lapping - for example ball bearings.

Twiglet · Jan 2, 2018

That looks electro-polished to me

gregormarwick · Jan 2, 2018

billzweig said:
Electro-chemical or chemical polishing leave a shiny finish but not precise surface. It is mostly used for decorative, food industry, high vacuum, high voltage - for parts that need polished surface but not perfect mechanical or optical accuracy. Buffing will have a similar effect. If both accuracy and finish are needed, it can be done by fine machining or grinding and then lapping - for example ball bearings.

Dimensional change from electropolishing depends heavily on initial surface roughness. It removes the high spots, so rough finish = significant dimensional change.

We make some parts out of 17-4 that have close tolerances that are electropolished after machining. As long as the surface roughness out of the machine is in the 0.2-0.4µm ra out of the machine, then the dimensional change during polishing is in range of several µm only.

OP's part certainly looks similar in finish to our 17-4 parts after electropolishing.

doug925 · Jan 2, 2018

As others have said, it is probably electropolished.
With the exception of the fin at the bottom, it could also have been burnished as the final step in the turning process.

Vancbiker · Jan 2, 2018

litlerob1 said:
......17-4, 304 and 316 finish absolutely beautifully. With a Wiper insert, high SFM and slow Feed I can get a finish pretty damn close to that right off the machine, with those SS's. I have achieved a 4µin. per the Profilometer.

I think this is pointing the right direction.

One screw machine place I installed several Citizens at would routinely do an 8µin finish as turned in stainless. Feeds were sometimes as low as .0002" per rev when cutting a .04" diameter.

5 axis Fidia guy · Jan 3, 2018

Looks like a diamond polish to me. Any mold shop can do that on almost any material.

DMF_TomB · Jan 3, 2018

certain carbide inserts leave a shiny finish when sfpm is high enough and ipt is in the minimum range often .0030" ipt
.
cratex rubber abrasive sticks i hold in plastic hand holders (same used for abrasive stick polishing of molds) and hold against part spinning in a lathe. if acts like a rubber eraser and smooths finish. they come in coarse, medium, fine
.
also just using a buffing wheel parts can be hand held against to make shiny. the softer the abrasive the more it blends corners or effects shape, profile, tolerances. the harder it is the more it will true up the profile. just saying if cosmetic finish usually do not worry about removing .0005"

Nerdlinger · Jan 3, 2018

Abdat60 - It looks a bit "cloudy" to me, like a foggy mirror...is it? If so, that would be vibratory finishing...different cutting/polishing medias used with different pastes/additives can smooth out machine marks and even shine them up like what I think I see. I do not think you can achieve a "perfect" mirror finish with that process but if it looks like there are microscopic dings a smudges on it when you look closely that could be your scumbag.

DMF_TomB · Jan 3, 2018

Nerdlinger said:
Abdat60 - It looks a bit "cloudy" to me, like a foggy mirror...is it? If so, that would be vibratory finishing...different cutting/polishing medias used with different pastes/additives can smooth out machine marks and even shine them up like what I think I see. I do not think you can achieve a "perfect" mirror finish with that process but if it looks like there are microscopic dings a smudges on it when you look closely that could be your scumbag.

.
i have seen shiny surface where you could see a tape measure in reflection but not like you can read the small letters in reflection
.
buffed parts often a object with zebra stripes is held and you look at reflection to see how straight the zebra stripes look in the reflection. if distorted its cause part is not perfect or distorted
.
picture buffing to mirror finish

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How was this Mirror finish achieved on stainless?

abdat60

Plastic

abdat60

Plastic

triumph406

Diamond

scadvice

Titanium

LKeithR

Stainless

litlerob1

Diamond

billzweig

Stainless

Twiglet

Plastic

gregormarwick

Diamond

doug925

Titanium

Vancbiker

Diamond

5 axis Fidia guy

Stainless

DMF_TomB

Diamond

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Nerdlinger

Stainless

DMF_TomB

Diamond

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