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.
Step 1: Cut Holes in Trash Can
*Sharp Edges, be careful!*
Mark and cut the holes for the trimmer shaft (actually this center hole becomes a lot bigger later on so the head spins freely)
Mark and cut holes for your hardware cloth screen. Leave enough metal/plastic to support the motor.
Step 2: Add Screen
Cut some hardware cloth to fit the bottom of the can.
Add some wood supports to hold the hardware cloth and strengthen the motor mount. Screw into wood from the inside of the can and snap off the screws if they're too long.
Also remove any shrouds on the trimmer so it can fit flush onto the base of the can.
Here I also cut the center hole bigger so the head spins they way it should.
I also added a plastic spacer at the base of the shaft so it sets the head a little higher to clear the can.
Step 3: Add Legs and Motor
Screw through the can and into the plastic shroud on the trimmer. Use washers.
I adjusted the trimmer head depth with wood blocks so the string is rotating .25" above the bottom of the can; any higher and it leaves large debris that clogs the screen.
(With the newer string trimmer motor shown I had to modify it with a wood donut as seen in the picture below.)
Plug it in and start tossing in the leaves.
Rules of this machine (lessons learned on some of these):
*Always unplug when adding new string or making any adjustments.
*This is a high speed low power motor; that means it can be easily overloaded. When it starts to bog down, it's too much.
*This works best with completely dry seed heads, moisture in the plant material makes the stuff bounce around rather than shatter.'
*Pulsing the trigger works best because the air current lifts the debris away from the head.
(I didn't have any leaves to shred while making the video, so I used newspaper instead. That's where I discovered it's use as a paper shredder too.)