Blue Skies wrote:
take a look at portable cement mixers for a starting point.

These are a little bigger than the tumbler I'm planning to make! I'm
thinking of a desktop model with a barrel diameter of perhaps 6".

By the way, has anyone thought of making a wind powered rock tumbler?
You could perhaps have a wind turbine with a shaft descending to ground
level and driving a concrete mixer type drum? Just a thought...

Best wishes,

Chris