Can I suggest you try out a rubber tire ( with no inner ) like a moto bike tyre to put your coins in.
You can't see the cleaning action and you need to know that your coins are sliding horizontal across one another, not "tumbling" as much. If you can see what the coins are doing, you will be able to find the correct speed to make them "slide" correctly
Nah u don't need a treadmill mate, just put the tire on the printrr rollers like your tumber tub mate. Get a small tire like a wheelbarrow one that will fit in it
What did u tumble them with ? They came up pretty good mate
I was told once to use kero instead of water , and also crushed up ceramic material and it gives a sheen rather than a dull finnish. Im yet to try it though .