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Polishing cast aluminum

Ultradog MN

Cast Iron
Joined
Jun 14, 2020
I'm working on cleaning up and painting an older machine.
It has a couple of cast aluminum belt guards on it - or some admixture of aluminum.
They were painted at the factory.
I was thinking about chemically removing the paint off of them and then polishing them.
It doesn't look like they were sand cast..
Too smooth a surface for that.
After stripping them, I could spend some time with a wire wheel in the pedistal grinder and then using a cloth buffing wheel to give them a shine.
Guess I should use some buffing compound too?
What kind of coumpound would I want and where to buy it. Also, what grit or grits would I want?
Lastly, is there a clear lacquer I could spray them with to keep the shine?
Now because you're all Practical Machinists, you're probably thinking what the hell do you want to do all that useless work for anyway.
Well, because it might be fun to add some bling to the new paint I'm putting on the rest of the machine and because, I'm fat, dumb and happy and can.
 

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Mtndew

Diamond
Joined
Jun 7, 2012
Location
Michigan
Before polishing, be prepared to do a lot of sanding to get the smooth surface that you want.
 

bosleyjr

Diamond
Joined
Sep 30, 2006
Location
SE PA, Philly
I've repeated here at least once the story Ben Franklin wrote about

"the man who, in buying an ax of a smith, my neighbor, desired to have the whole of its surface as bright as the edge. The smith consented to grind it bright for him if he would turn the wheel; he turned, while the smith pressed the broad face of the ax hard and heavily on the stone, which made the turning of it very fatiguing. The man came every now and then from the wheel to see how the work went on, and at length would take his ax as it was, without farther grinding. " No," said the smith; " turn on, turn on; we shall have it bright by and by; as yet, it is only speckled." "Yes," says the man, "but I think I like a speckled ax best." Count the cost of polishing. There's a reason the factory didn't do it!

Aluminum forms an oxide layer (same chemical as in sandpaper grains, and rubies!) which is hard and so Al doesn't tarnish. Unless you use something it finds corrosive which could be coolant or cutting oil. May be fine. Anyway, you shouldn't have to have a clear-coat on Al.

Myself, I'd paint it the same color as the rest of the machine. But you may want to enter your machine into the contest to appear on "Pimp my Mill". Good luck.
 

DrHook

Hot Rolled
Joined
Oct 8, 2013
Location
Pierre
You can make it "shine" pretty easily with almost any polishing compound, and some elbow grease. However, if you want a "mirror", that is a rabbit hole of multiple grits of sandpaper and compounds, and a buffing wheel. My vote is shiny it up and post pics and the story of how much effort you put in to it! :D
...full disclosure... I have never done it all the way to a mirror finish myself, but I have watched it done, and I "inherited" a shopful of stuff with my current job that I do not know how to use. I suspect the last person working here purchased all of it with company funds for his own use.
 
The paint was flaking off mine, so i sanded and polished those same parts.
Belt shroud you show, end/gearbox cover, and top/back gear cover.
I agree, it brightens up the lathe with "minimal" work. Certainly less effort than a paint job.

But "minimal" does not mean time or effort-free.
You have to get the paint off including around the details.
Then file and sand the castings smooth starting with about 120 and ending with 400 or finer.
Then decide how much further effort you personally look forward to. I use pumice. Maybe sometimes rottenstone.

smt
 

Vecair

Aluminum
Joined
Feb 19, 2017
Location
Prescott
If it makes you happy to do and see it everytime you come into your shop I say do it. I do plenty of meaningless little things to my machines when I have the idle time, I like the results and I like the thinking it takes to make them 'my own'. So it takes some time, I think it will look good and it will be yours.

Cheers mate!
 

implmex

Titanium
Joined
Jun 23, 2002
Location
Vancouver BC Canada
Hi All:
Just as a quick aside...if you are not very skilled with a buffer you can gouge the crap out of it and make it look like shit in a very short moment.
So get good with the buffer before you take on a high value piece.

Remember a 0.002" gouge is an obvious eyesore on a polished part...so don't gouge it!
Hand sand it until you're virtually there and then just kiss it GENTLY with the buffer to bring up the shine.

Cheers

Marcus
www.implant-mechanix.com
www.vancouverwireedm.com
 

Dan from Oakland

Titanium
Joined
Sep 15, 2005
Location
Oakland, CA
Don't wire wheel it- that will just add additional scratches that would need polishing out- Start by sanding with 180 or 220 frit and then go finer in steps with a final polish at the end.
 








 
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