I made this to shred leaves and break apart wildflower seed heads. This instructable shows an electric weed trimmer model; another instructable to make it gas powered is Gas Powered Shredder
. The gas trimmer seems to have more torque and lower rpm which keeps everything from shooting out of the top of the can.
A Round Trash Can
A Old Electric String Trimmer (gas if you're really good at mods)
Some Scrap wood 1x2s
.25" Hardware Cloth
1" Deck Screws or Similar Screw
Note: One picture below shows the machine upside-down; snap off the screw ends with some pliers.