Dave - if we are going to get into the engineering perspective,
let's talk about how far the steel moves to burnish the piece. In a
vibratory tumbler, the steel never really tumbles, it slides over the
work. In a rotary tumbler, it actually drops onto the work pieces.
Compare to a hammer planishing - it isn't going to do much at 1/16"
compared to an inch. If you want to slide stuff, do it with ceramic
beads, it's cheaper by far than steel.
Further, on the maintenance and care - yes I must oil the pillow
block bearings occasionally. My barrel is steel, doesn't leak, and in
twelve plus years, my belts have not broken nor do they appear worn.
I have however had two vibratory tumblers fail completely at the
Christmas rush. If my rotary failed, at the worst possible time, I
would buy a new belt at the auto store and be back in business the
same day. The vibratory tumblers require total replacement.
Here's something you may not have tried. When mass finishing to a
high polish, first run your jewelry in steel for 30 minutes, then in
the abrasive media for the normal cycle, and finish in the steel
again in your rotary tumbler. The work hardening done in the rotary
tumbler changes the crystalline structure of the precious metal
surface so that the smoothing of the abrasive media is more even and
the final burnishing is top rate. For a perfect shine, run more step
in a vibratory tumbler with dry media charged with simichrome for 24
hours. It results in a better finish than you can achieve by hand.