Polishing aluminum to a mirror finish?

[nautilus29]

Anyone have tips for polishing aluminum to a mirror finish? I have alot of experience polishing hard steels and carbide, but the same techniques don't work for aluminum.

So far I've been working my way up to 3000 grit sandpaper and then I polish using #3 diamond paste (yellow). It gives it a really good finish but not quite mirror. I'm not sure if I just need to go to a higher grit paper, or if diamond paste isn't right for aluminum.

 

[neilw20]

Have a look at jewellery forums. I know a jeweler that uses 8000 grit. You will have to find the forum for yourself, or others might respond.
There are special methods with EDM that can achieve 0.25 micron! But where will you get a machine that stable! University research stuff.

 

[gbritnell]

The only way I know of to get a mirror finish is to buff using a crocus stick. You have to be careful because you can round the edges very easily.
gbritnell

 

[michael-au]

I use Brasso for a mirror finish

 

[Cogsy]

I don't know if I'd call it mirror finish, but I use Autosol polish when I want the maximum shine I can get.

 

[Mechanicboy]

Use thin leather sheet or cotton clotch + chrome polish (Autosol to example) to make mirrorfinish. You can use rotating cotton disc, but be careful when polishing the aluminium since the metal is soft.

 

[Blogwitch]

I have found that Autosol gives a 'greyish' hue to aluminium surfaces.

To get a real chrome like finish to the work I used to do, I purchased a 'plastic' polishing wheel and the plastic polishing compound to go with it. The rotary wheel was very soft indeed, just like duck down. It is designed for polishing the likes of perspex..

http://www.caswellplating.com/small-plastic-polishing-kit.html

Aluminium castings come up like chrome, and stay that way because of the wax contained in the polishing soap.

The larger piece hasn't been brought to final finish in this shot, the smaller piece is finished.

John

 

[WOB]

Commercial wrought grades like 6061, 2024, 7075, usually polish nicely. Castings made from scrap (typical for model engine castings) and even some commercial castings may not polish to a mirror no matter what you do. So if you can't get the desired finish with reasonable amount of work, don't waste your time as it may be a lost cause.

WOB

 

[ninefinger]

Go and look in the car care / appearance aisle of any major store - there should be a polish for aluminum wheels there. Here in Canada I've used "Mothers" brand polish for aluminum wheels, works a real treat but it is time intensive to do a large surface.
http://www.mothers.com/02_products/05100-05101_b.html#yGFMjf56cHSiSuYh.97&slider1=7
Mike

 

[Naiveambition]

Here's my experience
I've done a fair share of different alum. The best finish will always be billet style alum. And degrades when cast, magnesium etc... So metal type is important in achieving a true mirror finish.
All of my compounds were bought bru Eastwood , sand to 400 at bare minimum, upto 1200 Be agressive with control on alum. Tripoli first then white. I like to start with a fresh wheel after an initial pass of white rouge. And be genourus on the last one with the rouge.

Two hard knocks lessons I've learned is if possible always change direction after each sanding/ buffing grit.

And always judge under sunlight. Fluorescents show and unbelievable amount of flaws but in natural light it will look amazing.

 

[rodw]

I'm with Cogsy and finish with autosol after working through wet and dry grades to about 1200 and some kerosene. Doing this on a lathe is quick and one piece used almost daily for about 3 years still looks nice and shiny

 

[Billitmotors]

If you are polishing a part spinning it in the lathe, like an aluminium cylinder head with or without fins, try using a fine Steelo soap pad used wet. Try getting the best possible machined finish you can without using abrasive paper before you start polishing. If you want an even better finish after using the soap pads, get some very soft flanalettte material, or even better soft cotton like old underpants material and use some Pennybrite polish which appears to be finer abrasive paste than Autosol.
ALWAYS remember to keep the size of the polishing pad as small as possible, so that it can't get wrapped around the job and pull your hand into the chuck.
Also it is best to cover the bed of the lathe with plastic to stop the water and even more so the abrasive paste getting on the bed.
Rob.

 

[nautilus29]

Thanks for all of the suggestions! I'll try some of these aluminum polishes and see how it turns out. I've been staying away from using buffing wheels because I don't want to round the edges of my part.

 

[Nick Hulme]

I've been staying away from using buffing wheels because I don't want to round the edges of my part.

Polishing is an art, part of which is choosing the size, material and direction of buffing wheel to avoid unwanted changes in shape, in general you will want to have the buffing action across a surface and only just reach, or drop off the edge, having the buffing material run up an edge then across a surface will round the edge significantly. There is a similar consideration when buffing paintwork where buffing over an edge onto a surface will usually strip off the paint ;-)

- Nick

 

[Blogwitch]

Here's my experience
I've done a fair share of different alum. The best finish will always be billet style alum. And degrades when cast, magnesium etc... So metal type is important in achieving a true mirror finish.

N,

You will notice that the picture I showed above is a cast material, and is well known for not being much good. These were from my own era, and know first hand how bad they were, you only had to tap the castings and spider web cracks appeared, in fact, on the larger piece, I had to grind out and repair such a fault before reshaping and polishing.

This shows the part having a rev counter boss being fitted. It is a shame that the spiders web can't be seen correctly, it is just to the left of the bright hi-light.

Dressing back to get the shaping correct.

I gave up on hand finishing with Autosol or any other tube or liquid based aluminium polishes because they just couldn't get the depth of shine that I wanted.

When the new plastic polishing wheels and soaps came along, it answered all my prayers, I could then get a hard chrome like finish on ANY non ferrous materials, including brasses and all it's ranges and all plastics. A thing that just can't be achieved by hand polishing.

People say that you get rounded over edges with buffing wheel polishers, but that only happens when you don't know what you are doing. In fact, I can sharpen up edges with the correct wheels and compounds.
Marvelous what you can do when it is done correctly.
BTW, I was shown all the tricks when watching the stainless polishers in R-R for a couple of years, doing their thing, they could work wonders with a scruffy old bit of welded up SS, which most of it started life as.

John

 

[nautilus29]

Looks like I need some practice using buffing wheels, and or a softer wheel. While doing some test runs with a buffing wheel I was having some issues with inconsistent finish. I noticed some of the info online suggests a softer wheel when you are close to being done, and I wonder if the hard felt wheels I'm using is hurting my feel.

After seeing some of the finishes you guys are getting I know it can be done! Thanks again for all of the tips!

 

[Blogwitch]

N,
I only use hard felt wheel when I have to remove large bits of machining marks or for digging out and flatting off large dings. I also use them to cut back radiused edges to get them square again, they really are like a soft grinding wheel, but only used to reshape metals, not to polish them.
After that, stitched wheels will start to get your shine. Once that is carried out and you have a sort of deep lustre the string cotton (plastic polishing wheel) comes into action to give you that chrome like finish that we all want.
If you are after a brushed effect to the finish, then invest in a brass wheel. This can also be used very effectively when cleaning up silver soldered parts. When it starts to become ineffective (brass wires bent back) then just turn it around on the pigtail and it will be just like new.

http://www.proopsbrothers.com/6x22-...ng-wheel-polishing-mop-brush-x1231-1130-p.asp.

There is a lot more to it than this, but these are the basics.


John

 

[bazmak]

I remember doing the cast iron fireplace with fine polish and cloth
we called it burnishing

 

[Nick Hulme]

I wonder if the hard felt wheels I'm using is hurting my feel.

Finishing wheels are a stack of cotton sheets sewn together.
Part of the advantage of these finishing wheels is that it's almost impossible to apply too much pressure, they are also the only wheel style which will work properly with a fine finishing polish, coarser wheels will leave artefacts and often lead to the conclusion that polishes like Autosol don't give a true mirror finish, they do if used correctly ;-)

- Nick

 

[goldstar31]

Ah Yes- the three B's or Bullsh1t Baffles Brains. The RAF Museum at Cosford has a DH Devon C1 which was originally made as a Dove and registered VP-952. She came to RAF Hendon in 1949 to replace the aging Avro Anson 19's of RAF 31 Squadron( The Goldstars)

She was polished by the pilot and he polished through the cladding and had to be rebuilt.

'981 was the boss of Coastal Command's private kite and it became the hack for the Battle of Britain Memorial Flight after its Hendon days.

They were ALL looked after by LAC John Leggett who also looked after Jimmy Robbs Spitfire SL-721-- JM-R which is still flying.

We're still mates though John is a bit shaky now

Happy Days

Norm