Polishing Machined Aluminum to a Mirror Finish





Introduction: Polishing Machined Aluminum to a Mirror Finish

About: I'm an Artist in Oakland, CA; formerly an Artist-in-Residence at Autodesk, Pier 9.

This is one of many strategies to get aluminum to a mirror finish. If you have sandpaper, a buffing wheel, and some compounds, you can get pretty close to mirror. To get clearer and clearer finishes, you can chrome plate, electro-polish, or do it the way NASA recommends.

Step 1: Machine the Aluminum

I started with machined aluminum from a Haas Mill, which saves a lot of sanding time. I recommend using the facing tool on all the flat surfaces you need to make shiny. End-mills are okay, but not as good. For this (kinda) cube, I rotated the piece and faced (with a facing tool) every side that was going to be polished. The sides of end-mills were leaving machine marks that were too deep.

Step 2: Sand to the Highest Grit You Have

Because I had machined it with a very precise machine before all this, I could start with 1200 grit wet/dry sandpaper. After getting rid of all the machine marks, I sanded it with 1500, and then 2000, giving it enough time on each to make sure all of that surface gets to that grit-level.

You can see from my set up that I clamped the sandpaper down using a random piece of metal, to a flat table that I've cleaned off before. (Any dirt underneath will only cause scratches in your finish). Wetting the paper makes it stick to the table as well, giving it you a flat surface to push against. Every once in a while, I would rinse off the grit in a bucket of water right next to my whole setup.

Step 3: Buffing Wheel + Rouge

The next and magical step is to hit the surfaces with a buffing wheel. At Pier 9, I used a cotton wheel on the Burr King and applied some brown rouge to to it, after knurling and cleaning the cotton a bit. Use the rouge sparingly, otherwise you'll end up with streaks of it on your metal. I placed a spongy mat underneath the wheel, just in case the Burr King caught an edge and flung it to the ground. Be sure to not even come close to the edge that will catch (like I did). Simply flip the piece around and buff from a different direction.

I sand and buff all in the same direction. This is not necessary, but it creates a uniform sheen on it at each stage which makes it easy to see what you have yet to sand/buff.

You should see it become reflective after just a light touch on the buffing wheel. Buffing it further will give it a little more clarity.

Step 4: Hand Buffer + Metal Polish

Apply some appropriate metal polish, and follow the directions on the back of the tube. At Pier 9, we have a buffing hand-tool with some nice cotton buffing heads. This saves some time and arm movements of rubbing the polish in. But after buffing it, you still need to rub the compound away with a clean microfiber cloth. If you watch the video, it's kinda magical to rub away this black tarnish to reveal a near-mirror finish.

And that's it! Be patient, and whatever strategy you use, try it on a test piece first. There are a lot of little nuances that only come with doing it a few times.

Step 5: Take Some Selfies

and don't touch it without gloves on. :)



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    So aluminum oxidizes very quickly,
    how does this effect the polish? Can we see some photos after 24 hours?

    7 replies

    Hello! Thanks for the comment – many others have expressed the same concern as soon as I showed them. The last polish I used (a California Gold brand) was also a wax that helped seal the metal. All the aluminum in these neon pieces were photographed a week after polishing: http://jimmychion.com/neon.html

    A week is nothing. A decade is the test of time for something that is worth doing instead of environmental waste/trash.

    You could use water soluable cystal clear polyurethane finish.
    That will last quite some time~

    Crystal clear polyurethane is not UV stable. If place in sunlight, it will discolor and eventually flake. Also, the polished aluminum piece will have to be cleaned very well prior to top coating as the buffing compounds leave behind a waxy layer that help prevent oxidation. I've done my share of aluminum polishing. It can be time consuming and frustrating especially working on a one horse buffer with a large buffing wheel. It's no fun when you have a prop spinner yanked out of your hand and then have to push out a crease in the tip of it.

    I've done mostly indoor. You are right. If clear coating becomes yellowish, semi-transparent discoloration, then there is no point to coat the aluminum with polyurethane.

    I will be sure to send you photos in a decade.

    Aluminum is a very soft metal so to get it to an A1 fishing is pretty difficult. Very great job. I'm a steel polisher. Have been for 9+ years. We work with various metals like 4200ss, elmax, s-7, etc. we rarely use aluminum just cause it's softness and ability to pit so easily.

    How not to pillow shape on grinding and especially polishing ?

    Way back in the early days of disk memory they used aluminum disks with painted magnetic material on them. This had it's limits, and they started to use deposited films on the aluminum. But, the old way of lapping the disk down to make them smooth enough wasn't good enough. They started to use a diamond bit in the machining process, and completely eliminated the lapping process. The diamond turning gave a smoother finish. All of the finishes were 'mirror' like, but the requirements for the disks were much better than a mere mirror finish.

    On your final finish did you have any pits.

    Wow! Incredible. And Thanks for the "how to" explanation. I suspect that there is a lot of skill, as well as knowing the steps.

    The best hand aluminium polish is proably 'Simichrome" about the only place to get it is motorcycle shops

    Shiney! Good job, I never seem to be able to get aluminum any where near that polished.