We purchased this tumbler as a christmas gift to tumble stones we acquired "gem mining" in the NC Mtns.First, advice: to keep the belts from slipping I used a bit of baking soda around the outside of the plastic barrel, which keeps it running smoothly. Without this, it was sticking a lot and the belt would come out of its track. Having figured this out, I was excited to see some final results, but nothing good to say there. While it seemed to go through the first few weeks of course and fine grit with decent results and improvements, we NEVER got to a final product that is shiny and nice. They are dull. Only obsidian type rocks (glass like to begin with) look nice. I tried double washing, extending the final polish, lighter loads, etc. to no avail. 3 full month long polishes and no nice rocks.I would NOT recommend this product at all. I'm looking for an upgrade!