Polishing Aluminium

Topics include, Machine Tools & Tooling, Precision Measuring, Materials and their Properties, Electrical discussions related to machine tools, setups, fixtures and jigs and other general discussion related to amateur machining.

Moderators: GlennW, Harold_V

pollys1dad
Posts: 296
Joined: Mon Jun 25, 2012 12:13 pm
Location: Wiltshire United Kingdom

Polishing Aluminium

Post by pollys1dad »

Can aluminum be polished to give a finish appearance almost, or just like like chrome, are some grades of aluminium better at this?
Any how to advice on method, welcome.
Cheers.
Last edited by pollys1dad on Mon May 29, 2023 4:45 pm, edited 1 time in total.
User avatar
Harold_V
Posts: 20231
Joined: Fri Dec 20, 2002 11:02 pm
Location: Onalaska, WA USA

Re: Polishing Aluminium

Post by Harold_V »

While I don't have anything to bolster my opinion, I would suggest that a high zinc aluminum alloy (7075 as an example) would come quite close to the color of polished chrome. Chrome has a blue highlight that is different from most aluminum alloys, although they do come close. That particular alloy is also relatively strong and machines quite nicely as well when properly aged.

H
Wise people talk because they have something to say. Fools talk because they have to say something.
User avatar
rmac
Posts: 787
Joined: Tue Jun 26, 2012 12:48 am
Location: Phoenix, Arizona

Re: Polishing Aluminium

Post by rmac »

I'm not sure what "just like chrome" means, but it's pretty easy to polish aluminum to a bright, mirror finish.

The first step is to use sandpaper to remove any and all scratches and tool marks. Start with whatever grit seems appropriate for the initial condition of the surface you want to polish. Then progress through finer and finer sandpaper until you get to, say, 600 or 1000 grit.

Each time you change to a finer grit, change the direction you are sanding by 90 degrees so you can easily see the scratches made by the previous coarser grit. At each step, remove ALL (Every. Last. One.) of the scratches from the previous grit before going on to the next finer grit.

Then put some white rouge on a buffing wheel and do the final polish. It'll be like magic.

I polished the engine in this old thread using this method. The material in the engine is plain old 6061 aluminum. It doesn't have that blue cast that Harold is talking about, but it is shiny.

-- Russ
pollys1dad
Posts: 296
Joined: Mon Jun 25, 2012 12:13 pm
Location: Wiltshire United Kingdom

Re: Polishing Aluminium

Post by pollys1dad »

Harold, " blue highlight " what does that mean?
Thanks.
Rich_Carlstedt
Posts: 1754
Joined: Sat Dec 21, 2002 12:16 am
Location: Green Bay Wisconsin USA
Contact:

Re: Polishing Aluminium

Post by Rich_Carlstedt »

We polished the aluminum covers on our dies at work
We used "Simichrome" polish-- wow did that work
It may be more expensive but you see your face in the reflections
Rich
User avatar
Bill Shields
Posts: 10460
Joined: Fri Dec 21, 2007 4:57 am
Location: 39.367, -75.765
Contact:

Re: Polishing Aluminium

Post by Bill Shields »

Getting it polished is one thing. Having it stay that way is another 🤔
Too many things going on to bother listing them.
User avatar
Harold_V
Posts: 20231
Joined: Fri Dec 20, 2002 11:02 pm
Location: Onalaska, WA USA

Re: Polishing Aluminium

Post by Harold_V »

pollys1dad wrote: Mon May 29, 2023 4:49 pm Harold, " blue highlight " what does that mean?
Thanks.
Hard to explain unless you've paid attention to the slight color differences in metals. Stainless steel, 300 series, has a slight yellow cast to it when compared to a different alloy, say 440C, which contains chromium. When compared to even carbon steel, the color is obvious that the 300 series is tinted yellow.

Steel looks quite white (silvery, really) but when compared to aluminum or silver, it isn't nearly as "white", having a rather gray tint. Both lead and zinc tend towards a blue tint, similar in nature to chromium. It should be understood that I am not talking about luster--just color.

If you pay close attention to chrome plating, you'll see that it leans towards blue. That is easily noticed when you have a white metal near so you can see the difference, like pure silver, assuming it isn't sulfated (turned brown to black). That's really one of the easiest ways to see what I'm talking about.

Here in the states Harley Davidson produces bikes that are highly desirable to old guys. They use both chrome and aluminum, highly polished. They look quite nice when new. Armed with that thought, do a good job of polishing and the slight color tint difference isn't likely to be an issue, especially if you choose an aluminum alloy that leans towards blue at the outset.

Bill commented about aluminum staying polished. Yeah, that's a whole different matter. It readily oxidizes unless well protected. That's one of the reasons that aluminum is commonly anodized.

H
Wise people talk because they have something to say. Fools talk because they have to say something.
Mr Ron
Posts: 2126
Joined: Tue Dec 22, 2009 12:36 pm
Location: Vancleave, Mississippi

Re: Polishing Aluminium

Post by Mr Ron »

Doesn't the reflectibility of the metal depend on the temperature of the light source used?
Mr.Ron from South Mississippi
Mr Ron
Posts: 2126
Joined: Tue Dec 22, 2009 12:36 pm
Location: Vancleave, Mississippi

Re: Polishing Aluminium

Post by Mr Ron »

Rich_Carlstedt wrote: Mon May 29, 2023 7:25 pm We polished the aluminum covers on our dies at work
We used "Simichrome" polish-- wow did that work
It may be more expensive but you see your face in the reflections
Rich
Simichrome polish was supplied to Volkwagen owners to polish the chrome bumpers.
Mr.Ron from South Mississippi
pollys1dad
Posts: 296
Joined: Mon Jun 25, 2012 12:13 pm
Location: Wiltshire United Kingdom

Re: Polishing Aluminium

Post by pollys1dad »

Harold_V
Very enlightening reply, thanks for that. Just been reading up a bit, https://en.wikipedia.org/wiki/Anodizing#Aluminium
" choose an aluminum alloy that leans towards blue at the outset. " What grade would this be? If I have a choice, what grade/s would produce the best result?
I'm very new to the world of machining but I do have a machinist friend in his 70s who has done little jobs for me in the past. He is the secretary of the local Steam Locomotive Society. He has a big Warco lathe and mill in his garage.
I've mentioned to him if making a pedal steel guitar, S-10, single neck 10 string would be something do able for me, or completely beyond me? I've sent him a few emails about my idea, he is very busy just at the moment but will reply in full a bit later. He says he has many years of Model Engineering magazine that are looking for a new home.

In anticipation been reading up a bit.
How to Machine Aluminum: All You Need to Know
https://makeitfrommetal.com/how-to-mach ... d-to-know/
Machinist Tools: Edge Finding,
https://hackaday.com/2019/07/31/machini ... e-finding/
A Buyer’s Guide To Lathe Options
https://hackaday.com/2018/04/24/lathe-f ... t-machine/
Also been reading Milling Cutters Explained,
https://en.wikipedia.org/wiki/Milling_cutter
Also see, Milling (machining),
https://en.wikipedia.org/wiki/Milling_( ... g)#History
Are there any books to read that would be helpful, YouTube channels to watch and learn?
Thanks again.
Ps other people who replied, thanks for the input.
User avatar
liveaboard
Posts: 1971
Joined: Sun Dec 08, 2013 1:40 pm
Location: southern Portugal
Contact:

Re: Polishing Aluminium

Post by liveaboard »

I also polished up some aluminum motorcycle engine covers; it was quite easy and the polish was great.
For a few months.
A year or two later, they were completely grey again.

You need to way of varnish after polishing. But wax doesn't last, and varnish peels.
User avatar
Bill Shields
Posts: 10460
Joined: Fri Dec 21, 2007 4:57 am
Location: 39.367, -75.765
Contact:

Re: Polishing Aluminium

Post by Bill Shields »

old-fashioned hair spray works for a reasonable while on brass and aluminum -> is easy to remove
Too many things going on to bother listing them.
Post Reply