I made this for breaking up seed heads for prairie restoration, but it ended up being an good leaf shredder too. I made an electric one earlier, but this gas powered one works so much better because of the lower RPMs and higher torque. This is very fun to use, the neighbor kids raked my whole yard just so they could throw leaves into this thing.
When collecting wildflower seeds for prairie restoration, hundreds of seeds can be enclosed in a seed head, (think of sunflowers.) I needed a way to quickly and cheaply break down the heads to extract the seeds for broadcast planting. Sure I could pay someone to process the seed or I could buy the expensive equipment, but this seems to work well and cost me about $5. I picked up almost everything from curbside trash at spring cleanup. The $5 went to new fuel line to fix the junked weedeater and to some .25" hardware cloth.
This doesn't work well with hard seed heads like echinacea, penstemon, and rose hips. For those seeds I made a smaller version of this using a five gallon bucket and a blender motor. That thing really rips things apart well without damaging the actual seeds.
A round 30 gallon trash can, already had this, new $20 (Use a plastic can, this metal one cuts the line a lot where the screen is attached.)
Gas power string trimmer, free or $60 new.
Lawn mower handle, free from junked mower.
.25" hardware cloth.
Some scrap wood, 1x6 board, 1x2 and 2x2 pieces.
Curtain rods or plumbing strap.
Deck screws and some bolts.
A throttle adjustment lever from a mower.
Step 1: Cut the Trash Can and Add Mesh.
Cut three or four sections out of the bottom of the can with a drill and some tin snips. Make it look like a wheel with 2" wide mags. Cut the mesh/hardware cloth to fit the can. Use some 1x2 pieces of wood to reinforce the mags and hold on the mesh. Drill screws into the wood from the inside of the can. Snap of the screw tips with pliers if they're too long.
CAUTION: SHARP METAL EDGES HERE!
Step 2: Make Legs and Motor Mount.
I used an old lawn mower handle to make the legs. Take the handle off the mower deck and take the two pieces apart. Use a pipe wrench to twist the handles so the flat tips match up with the can as shown in the picture. You may have to flatten the tips with a hammer and drill your own holes in the handle depending on the mower manufacturer. Drill through the can and put the bolts through the holes from the inside so the nut is out.
Attach a board to the bottom of the legs to mount the motor.
Drill holes in the bottom of the legs to attach the 1x6 or 1x8 board with screws. The length of the board depends on how much you shorten the weed trimmer shaft, This one is 2.5' long.
At this point you may want to attach small stabilizer 1x2 boards perpendicular to the motor mount board.
Step 3: Prepare the Gas String Trimmer.
Remove the shaft from the trimmer (save all the parts.)
Bend a 90 degree in the shaft with a tubing bender.
Remove the drive cable and shorten the shaft with a hacksaw; I removed about 12" for this project. (Remember how much drive cable sticks out the end before the cut.)
Cut the drive cable with some bolt cutters.
Now you need to make a new tip for the drive cable with a grinder or file; just grind the fresh cut tip to the right shape. I think generally they're square tipped.
Step 4: Mount the Motor and Go.
Before attaching the shaft to the motor, slide the loop handle grip back onto the shaft and use it to prop up the trimmer head into the can; look at the picture to understand this better.
Center the trimmer head in the trash can and adjust it so the string spins .5" to 1" above the bottom of the can. Use something to screw down the handle to the board once you have everything lined up; I used half of an electrical fitting clamp.
Use some wood to block up the engine like in the picture. Then use plumbing strap or whatever else you have (I used flattened curtain rods) to brace the motor to the board.
You can mount the hand trigger throttle assembly to a lawnmower throttle adjustment lever so the rpm's can be set to be constant; thus freeing hands for loading seedheads.
Step 5: Video, Tips, and Extra Pics.
Wear eye protection.
Wear respiratory protection if you're sensitive to allergens.
Clean the engine air filter often because this makes a lot of small debris.
Use a piece of wood to tap the button on the trimmer head to let out more string when needed.
Don't forget to lay out a tarp to catch your seeds.
I considered adding wheels, but this is pretty light and easy to carry.
A patched together video, some sound is missing because of the old camera.