Any good suggestions for removing a scratch from the brushed aluminum finish on the back of a new imac, case of a unibody, mac pro, etc?

I have an imac here that I have been asked to remove a scratch from the back of and I know from past experience that merely trying to sand/polish it off doesn't work out. Sanding tends to produce parallel scratching (which is hard to impossible to randomize) and doesn't rapidly remove the scratch. Polishing removes the scratch but leaves a mirror finish in contrast to the brushed look around it.

The only other option is to replace the rear housing. For which the relevant adjectives are "unpleasant", "involved", and "expensive".

A random orbit sander will not leave the parallel marks and if you use say 400 or 600 grit any scratches would be too fine to be seen by the unaided human eye but that might produce a shine as well.

From my experience in woodworking, I would try buffing the back with a linen buffing wheel with perhaps a bit of white diamond polishing compound. If the scratches are too deep for the white diamond I would switch to a canvas wheel with Tripoli buffing compound. If the buffing leaves the surface too shiny I would "break" the shine with 320 grit sandpaper on a random orbit sander. That will leave a very slightly roughened surface but the random orbit sander does not leave any parallel or straight sanding lines.

Random orbit sanders can be found anywhere woodworking tools are sold. The ultra fine grit (320, 400, or 600) sandpapers are harder to find, but any store catering to woodworking such as Rockler's or Woodcraft will have sandpaper in those grits.

I discussed use of such a sander with a professional fabricator I know and after looking at the finish he said that's probably not going to work, and had no better suggestions. I may give it a shot anyway, I have another spare rear housing to do some test on. Any other ideas welcome.

Your surface texture may require chemical etching to restore from edge to edge and make it look uniform after removing the scratch......or possibly shot/bead/sand blasting.....either way, it would be more work to try to repair the scratch than to replace the back.

Yes I was wondering if it might be chemically etched. Hadn't thought about shot blasting but that's certainly another way to get an even brushed look. Thanks for the info, I'll keep looking also, but it's looking bleak.

Years ago, I spoke with someone at the now defunct Apt Corporation about their black finished aluminum front panels. He told me that they were glass bead blasted anodised aluminum, and that after blasting, the edges were taken off the craters with a chemical before they were anodised. The final surface was alleged to be harder than steel. Unfortunately, at the time, nobody in the USA was offering to do this treatment (which cost 10 cents per square foot) so the front panels had to be shipped to Japan.

harder than steel but scratches like plexi

Virtual1,

Not much of an advertising slogan, is it?

I used to use Simichrome on my Honda.
[just joking... but then again, who knows]