Polishing aluminum

BlownMGB-V8 · November 04, 2011, 11:43:32 AM

I'm looking for a few production type tips on prepping a large rough surface for buffing. I'm in the range between a flapper wheel on an angle grinder and the final finish. As you guys know, you can only get so smooth with a flapper wheel and it leaves swirl marks and gouges. From there I've gone to a 7"dia x 2" wide rubber faced sanding drum on a 3400 rpm pedestal grinder, then a 6" dia x 1" 80 grit loose bonded flapper wheel, and I have a 3m scotchbrite/flapper v-fine grit 6 x 1" wheel ordered.

What I'm hoping to do is get the finish worked down to a nice smooth satin so that the buffing operation will be quick and easy, but I'm working with a very large area and don't want to spend the rest of the winter getting it done. I have some buffing compound that I picked up at the local truck stop, a big dark gray bar, plus some old stuff, one is white and the other is a sort of reddish brown. I know some of you have worked with this stuff enough to know what is what and I'd appreciate any tips you can send my way.

JB

roverman · November 04, 2011, 12:43:14 PM

Picture would help. I've learned , use buffing compund/stick, for aluninum only. You might ask a buffing/polishing shop ? Good Luck, roverman.

Bill Young · November 04, 2011, 12:56:40 PM

Jim, the polishing compound sticks are color coded by grit. The grey is the most aggressive with the white being the finest. I had good luck in the past using red compound on a sewn cotton buff, gives a nice luster, but not quite a mirror type finish. Use the grey first to polish out the marks from the flap wheel and then change buffs and go to the red compound. The white does a nice job on stainless steel. For large areas that you can't hold up to a spindle mounted buff you can get pretty good results from a standard 7" polisher, but it will take some time as the force you can use is much less than you can apply if you can lean into the work. I was working on rather small pieces and small areas on the blower case and valve covers and a 7" buff mounted on a 1/2 hp electric motor I mounted on the shop wall worked fine.

BlownMGB-V8 · November 04, 2011, 07:07:20 PM

Once I get it smooth enough to buff I think I'll be fine with it but getting to that point is the challenge. I have 3 pieces I'm working with, the inlet housing for my blower (scoop) which is 6061-T6 and the stainless stringers that bolt to my inner fender flanges. The stainless is fairly smooth but has marks that show up when buffed, and they are pretty slow to buff and quite long so I think more polishing would really help a lot on those. The same really applies to the aluminum housing but it isn't as smooth to begin with.

As far as changing the buff, that really isn't much of an option. My buffer is a large frame 3 phase motor with about a 2" shaft on which is mounted a 2" thick stack of 16" dia. x 1/2" thick spiral stitched buffs. Changing buffs would be neither easy, cheap, or fast, but on the plus side, nothing I can do is going to slow it down.

So I guess I'll be mixing abrasives, but I'm not overly concerned with getting a mirror finish and if that changes I guess I can rake the buff to clean it out, provided I can find something to rake it with. I'm not too worried about that yet.

Has anyone tried that red scotchbrite wheel with the emery flaps in between the scotchbrite? I'm just wondering how aggressive it is. If it will easily take me from a rough satin finish down to really smooth but still dull then I'll be in business.

JB

roverman · November 04, 2011, 11:39:35 PM

"Cermachrome" works on aluminum-hint.

BlownMGB-V8 · November 05, 2011, 12:02:01 AM

Yeah, there's an almost identical product called Met-all that comes in a decent sized can (a pound or two I think) at a fair price. But the metal has to be smooth first, and I'm not there yet.

JB

BlownMGB-V8 · November 15, 2011, 05:07:35 PM

Guys, thanks for the help. I got my parts polished and while they aren't perfect I think it's pretty good for a prototype.

I ended up using a 180 grit flapper wheel, followed by the red scotchbrite wheel and then took it to the buffer where the dark gray abrasive and lots of pressure did the rest. I'm satisfied with it. I don't really care that much for polished aluminum as it's just another thing to keep up with, but maybe over time it'll develop a nice patina.

JB

roverman · November 16, 2011, 08:01:14 PM

Jim, the way youv'e built this beast, woudln't be the latter ? Go fast, go safe. roverman.

74ls1tr6 · November 18, 2011, 10:00:26 AM

Jim,

Put Sharks hide on your aluminum, it will coat it. Easier to keep it looking nice.

http://www.sharkhide.com/apinfo.html

I put this stuff on my steel steering shaft, a couple of coats, and I have no surface rust showing yet. Soon I will put it on my rims before the rain hits here, and my aluminum boat after cleaning.

http://www.sharkhide.com/mpinfo.html