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Where I work we have a polishing machine,basically a big buffer wheel,I recently polished up some M960 XTR cranks,I can now see my reflection in them When the wheel grabs it tends to throw stuff quite a long way though
For those, I would scrub with a brillo pad and hot water. Then work with the autosol. If theres any heavy scratches that your bothered about try some wet and dry. If you think you might do some more stuff and have access to a pillar drill, buying a mop and cutting compound is the way forward. Soooo much less time consuming.
Personally I like Damian's approach. I like to use 1000 and 1200 grit and then finish with a white scothbrite sheet and almost any finishing polish to put the mirror on them. I too have done the XTR blue/grey cranks and that's some of the toughest finish in the world to work through but they turn out great.
Polishing by hand is a great feeling but takes time and patience. If they are scratched then there's no alternative than to get abrasive using wet and dry. The severity of the scratches will determine the grit of yet and dry needed. I'd say 600 will be a reasonable start point. When the deep scratches are out the cranks should be smooth but dull. You now need to go through the grades of paper all the way down to 1200. By this time any scratches on the cranks will be very smooth but still dull. Time to break out the autosol and then the brasso. The wet and dry is far far more important than the polish. The smoother the cranks before you break out the polish the better the final finish. Use plenty of soapy water with the yet and dry. Tea helps too. Milk, no sugar please