Tumblers are really burnishers. The require the items put in them
to be free of scratches. If you put an item in a tumbler with
scratches, you'll get out a pieces with shiney scratches.
This applies to tumblers being used with steel shot. Put items in a
burnishing operation, and guess what, you get only burnishing action.
But tumblers can do more than burnish. Start, instead, with
abrasives, such as the various abrasive cone media, and these then
are able to refine rough unfinished, or roughly finished surfaces, to
ones with then finer scratches and fewer defects. Switch to a finer
abrasive media, and you may then end up with a surface that’s matte,
finished to a higher degree. Switch again, perhaps to a burnishing
operation (steel or ceramic media), and then you get your burnished
finish when the original items were quite rough and perhaps
scratched or filed.
You can also use media other than steel burnishing shot. Walnut
shell with rouge or polishing compounds, when applied to work with a
sufficient preparation before, can indeed give you a very high level
it is possible, but not so easy, to get a tumbler to finish metal to
almost the same level of finish you can get with hand buffing. The
main difference is that with hand buffing, you can do things like
respect and refine edges, while tumbling tends to finish everything
uniformly, which will soften and round edges and corners.
But simply buying a tumbler is just the first step. It LOOKS like an
automatic tool, put the stuff in, get magic out, etc. But it’s not.
It takes some experience to know what sequence of media, how to use
them, for how long at each step, and what level of prefinish is
needed, etc. It’s not surprising that a new user of a tumbler,
especially if using just steel shot, could be disappointed with not
getting a super high polish. But that does not mean the tumbler
isn’t capable of giving you that level of polish. You just cannot do
it with only steel shot. Steel shot, used right, is fast and easy,
giving a nice level of uniform finish that may be just right for some
things, and the burnishing action, which other tumbling abrasives and
media don’t give you, is great for improving the surface of castings
which may otherwise suffer from a bit of porosity. But it only does
what it does. To get it all (super polish from rough) takes a good
deal more than just steel shot.
Take a look at the level of high polish easily attained on tumbled
semiprecious for example. From rough crushed rock to
shiney softened usable bits of ornamental material, or from preforms
to finished cabochons and the like. Getting this requires the proper
sequence of abrasives, used correctly. But with lapidary tumbling,
such results are pretty routine. And there’s no reason you cannot
get a tumbler to give you the same level of results with metal, if
you also follow the same degree of care and proper process.