I also use a tumbler, mine from Harbor Freight was closer to $30 but it's still way cheaper than what you can find even on eBay. I'm still working on getting the "formula" just right, but here's what I've found so far:
Absolutely separate the clad (nickels, dimes, quarters) from the pennies, otherwise your clad will pick up a golden sheen from the pennies. For clad I put about a fistfull of coins (not too many or they won't have room to tumble) in the tumble drum, add aquarium gravel (for clad I use the slightly larger white gravel from Walmart) up to about 3" from the top of the tub, then add about two tablespoons of clean sand. Top if off with a squirt of Dawn or other dishwashing detergent (about a tablespoon) then add water to cover the whole mix by about 1/4". After you put the top on the tub give it a few rolling shakes to mix everything up, then tumble on the machine for 10-12 hours. I know this sounds like a long time, but these rock tumblers are made to run for days on end. I'll usually start mine in the evening and let it go overnight.
After 10-12 hours I turn off the machine, pour the tub into a kitchen strainer (not down the sink or you'll need a plumber soon because of the sand and any gravel that misses), and wash everything off. I made another strainer out of 1/4" wire mesh, I set this strainer in a cookie sheet and pour the cleaned gravel/coins in this. A few shakes leaves me with coins in the strainer and wet gravel on the cookie sheet, the coins go on paper towels to dry and the gravel goes in the oven on "warm" for 5 minutes to get it drying for reuse.
For pennies I do the same thing except I use the small blue gravel, no sand at all, and I add a teaspoon of cream of tarter. The cream of tarter acts as a chemical cleaner for brass and copper. I usually run pennies for only 6 hours before checking them, they might need to go longer but usually it only takes 8 hours or so at the most. Strain, rinse and everything else just like the clad.
What I like about this system is that the gravel is cheap and everything else is in the cupboards or around most homes. Personally I don't want to use a lot of chemicals to clean the coins and I don't want to spend a lot of money on specialty tumbling media or mixes. All it takes is time and a little effort.
I've had mixed results so far. Sometimes the clad coins come out clean as a whistle, you can't tell the difference between a tumbled coin and one from your pocket. Sometimes the sand blasts them to a dull shine. There are always half a dozen coins that just don't come clean, and I put them aside for another go with the next batch. Some coins don't come clean no matter what. You can either save coins up to turn in at the bank or use them in vending machines for stamps, snacks, whatever.
The pennies are usually VERY clean and shiny, especially the ones from the 70's. I don't know why. Of course the zinc pennies ('82 and later) will usually have pits from corrosion depending on the soil condition you pulled them from, if they look like they'll go through a counting machine I put them in a butter tub. The older copper pennies I put in a mason jar and don't know what I'm going to do with them yet. I was hoping to sell them as scrap since copper scrap is $3/pound now, but I heard it's illegal to sell US coinage as scrap. I'm just going to hoard them until I figure out what to do with them.
Of course follow all manufacturer's instructions on the tumbler, keep the kids and pets away from it's moving parts and experiment for yourself to find what works best. DON'T tumble wheat pennies, coins of any value higher than face value, or silver. If you come up with a foolproof formula let me know, I'm not too keen on using a lot of chemicals and stuff that I have to worry about.
Hope this helps,
Steve
