Polishing Cast Aluminum

[nikos8]

I have a cast aluminum intake with a rough surface which I would like to polish. Can someone walk me trough the steps of which wheels and compounds I would require? Also what's the best way to keep it nice and shinny afterwards?

Thanks
Nick B.

[tvsp]

I'm interested in the answer to this, too. I have some aluminum parts that were sand cast & want them to look flawless. From the polishers & finishers at a local shop, I was told to use a die grinding disc (air tool) with #80 sandpaper, then #120, then 2 grades of 3M pads, then (optional) tumbled with 3/4 plastic cones, then wheel & compounds.

[mpierich]

Originally Posted by tvsp

I'm interested in the answer to this, too. I have some aluminum parts that were sand cast & want them to look flawless. From the polishers & finishers at a local shop, I was told to use a die grinding disc (air tool) with #80 sandpaper, then #120, then 2 grades of 3M pads, then (optional) tumbled with 3/4 plastic cones, then wheel & compounds.

That's the general idea, but you certainly won't get into all the pockets with discs. That's what cartridge rolls (amongst other tools) are for. Assuming you're also talkng about an intake manifold. I use rolls from 120 to 320 plus a couple of oher gadgets.

I used to begin with 80-grit but found it an unnecessary step. 120 usually works plenty fast and doesn't leave massive scratches to sand out.

Not sure what 3M pads you'd use. And again, if you're talkng about an intake manifold I am truly interested in specifics of how you "tumble" something like that.

[alabama_lowlife]

depending on how rough the casting is, you can start with any type of grinding device to get the BIG ridges out. like the ones left from where the mold halves went together. in some cases you'll have to use sandpaper, but in others you can just use greaseless compound on a sewn cotton wheel to smooth the rough surface. it dries on the wheel like a soft grinder and takes of aluminum pretty well. in most cases it'll come down to what spots on the intake you can get to with which tools. you may have to use a dremel or something similar to get alot of places.

after you get the coarseness out, you start with emory on a sewn cotton wheel and then tripoli on a sewn cotton wheel, followed by white on a loose section or cushion buff.

keep in mind none of this is set in stone. you will have to experiment to get the right combination for each work piece. tripoli causes hazing on some pieces. just take some time to read through alot of the threads on here. there is alot of information here.

[tvsp]

Sorry, I said tumbling for my small parts, not for a manifold. And my parts also have no nooks & crannies, thus just the discs.

[jrow]

nikos8,

I have successfully used a metal file to remove the mold marks from the casting process. They make files especially for filing aluminum. You can also use a diamond impregnated fingernail file to do the same thing. If you are using a die grinder with cartridge rolls, be careful they will gouge when you move from one direction to another. On flat surfaces you can use a DA sander, it will leave a nice flat surface when done properly! I would also recommend the greaseless compound to get the aluminum to the place where you can start to buff it. I would suggest that you get treated buffs ranging from 1" to 3" for use with the greaseless. When you start sanding your project, match the grit of your sanding media with the finish of the part you are going to sand. That's a good starting place! You can normally start to buff after you have sanded with 600 grit paper. I wet sand with that grit using water and a little bit of dish washing liquid. That helps to keep the paper from loading up. Prior to starting to buff wash your aluminum in hot water and dish washing liquid, Dawn. After you start to buff use acetone or brake cleaner to clean the aluminum.

There's plenty of information on the site on aluminum polishing, go through that it will give you further information.

John

[nikos8]

Thanks for all the input. I have found a lot of info on the polishing and buffing stage but only general answers as to how I would start off. There aren't many casting seams on the manifold. It's mostly the "sand" finish on it that I was confused on how to smooth out.

Thanks for all the help.

Nick B.

[mpierich]

Originally Posted by alabama_lowlife

...in some cases you'll have to use sandpaper, but in others you can just use greaseless compound on a sewn cotton wheel to smooth the rough surface. it dries on the wheel like a soft grinder and takes of aluminum pretty well...

I can never use greaseless on an edge or a ridge - it drags the compound off the wheel in short order, even when I've put on 3 well-cured layers. Any tips?

[alabama_lowlife]

oh no, it definately won't work on sharp edges. i should have been more specific on that aspect. it gets taken right off if you try to use it on an edge. i meant the overall roughness of the casting. the nissan valve covers that i am usually working on don't really require alot of grinding of edges so i usually just go straight to the greaseless.

[Tng21]

greaseless it great stuff, i started this thread a while back , see the inlets im doing

Sanding questions

and this is what they look like after the greasless and a bit of polishing

Inlet polishing progress