Getting a mirror finish on aluminum in a vibratory machine requires a couple different media......first use fine grit plastic triangles for 24 to 36 hours. Then use rouge treated walnut shells for another 36 hours. The part has to have smooth surfaces when it goes it the machine. You could use a more agressive media initially, but as it cuts away mill marks, etc it will also be eating away at the other features of the part. Vibratory polishing isnt selective. On turned parts where the proper aluminum-specific inserts have been used for machining, the surface will be sufficiently smooth with no hand prep. Most milled parts require some sanding, and a small vibratory sander works well....better IMO than hand sanding and not nearly so tiring. I've got a couple vibratory finishing machines in my shop, but after fooling around with polishing aluminum parts in them I decided it was too much of a hassle. Here's a part I make. Once the sanding is finished, the whole thing can be buffed out in ten minutes. It's a nasty job, but it makes stuff purty
