Most shredders are similar in design. There is a hopper on top in which to dump loose material, and a side opening through which to feed pruning clippings and small branches. Shredders differ primarily according to the size of the hopper, the size and type of the cutting devices, and the power of the engine.
The hammer mill method is most common for shredding materials of small to average size. Rows of free-swinging, short lengths of metal are fixed to a drive shaft that flails the plant material into small pieces.
The material is held in place near the shredding devices by a metal screen with holes about 3/4 inch in diameter (in the standard version). When the hammer mills have broken the material down far enough, the material passes through these screen holes. Some manufacturers offer a wide choice of screens, with holes ranging from 1/8 inch up to 2 inches so that the user can vary the size of shredded material. Most models also have a roller bar system that’s used instead of the screens for handling wet or green material that doesn’t pass through the screen holes easily.
Once the material is cut, it is thrown out a chute on the shredder’s bottom or side. Some models come with a pan to catch the debris; others provide bags. In both cases, the purpose of the container is to move the shredded vegetation to the compost pile or to the garden for mulch.
Selecting a Shredder
Shredders come in electric and gas-operated versions. In deciding which to buy, consider how far from a power source you must work. Gas models can be taken anywhere, even into the woods to shred a pickup’s load of fall leaves; electric shredders must stay within reach of the nearest electric outlet.
Engine sizes range from 3 to 8 horsepower. Obviously, the larger the engine, the heavier the material it will handle—but the cost also increases proportionally.
Better shredders are built of 12- to 16-gauge steel; less expensive ones are made of sheet metal. Steel has the advantage of greater strength and durability. Screens should be readily accessible so that you can change them according to the size of compost desired, or remove them when they get clogged. If you live in a wet climate, be sure to get a model with roller bars in addition to the screens.
- Always wear protective goggles when working around a shredder.
- Never push material down the hopper with your hand. Use a stick.
- Do not let children feed the shredder or even play nearby when it is operating.
- Unplug the power cord on an electric shredder or remove the wire from the spark plug on gas-operated machines before attempting to clear a jam. Make sure the plug wire will not fall back against the plug.
- Know how to turn the machine off quickly—you never know when this may be important.
Follow the manufacturer’s recommendations for cleaning, sharpening, and lubricating. In general, cleaning involves washing out the hopper to remove the residue and keeping the screens unclogged. Check the hammer mills, or steel flails, at least once a year (more often if they are used extensively). If any are broken, replace them.
Gas-operated shredders require routine engine maintenance. Virtually all shredders use a four-cycle engine, so the oil needs to be changed about every 25 operating hours. Use a 30-weight oil or whatever the manufacturer recommends. Consult the owner’s manual and follow the engine maintenance and tune-up guidelines in Tuning Gasoline Engines.
If the shredding devices don’t work but the engine does, the problem probably lies with the clutch or the belt. Check the owner’s manual for trouble-shooting advice. If the problem isn’t something you can handle comfortably, take the shredder to a competent repair shop or to your dealer.