Wow 
I had a tumbler 30 years ago, i was right into gemstones & rocks, and dad bought me a tumber for xmas, it ran 24/7 turning my horrid rocks into .....well..... "smoother" horrid rocks (i never quite got a 'gemstone' come out).
MY tumbelr from from a local lapidary club (gemstome shop) back in the day, but there might be better range at todays gem shops, wherever they may be?? maybe sold at mining (metal detector) shops?
I would have thought these days a mini ultrasonic bath (jaycar etc) would be used for cleaning parts?
Also try the Oxalyic Acid from Bunnings for rust removal brings things back to original chrome/nickle/zinc again.
Marty Machine.
I'd like to try the ultrasonic method to clean parts. I hear it is particularly good to clean ribbed plastic posts etc..
