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Gardening Articles: Care :: Soil, Water, & Fertilizer

Garden Grinders (page 2 of 4)

by Michael MacCaskey

Shredding Components

Shredding hammers. In addition to the chipping component, chipper-shredders have a separate shredding unit that handles soft or thin material, such as leaves and compost. The hardened steel blades, called shredding hammers or flail knives, are about 3 inches long, 1 inch wide and free-swinging, like the seats on a Ferris wheel. The shredding hammers are located just below the shredder hopper, where the material is deposited into the machine.

The hammers hang when at rest but are flung outward during operation and eventually contact the material you're feeding into the machine. If a shredding hammer hits a stone or something hard, it bounces back sustaining minimal damage in the process. Some shredder units include fixed knives that are attached as rigidly as the name implies. Although they'll cut more aggressively, they also wear much faster.

In most machines, fixed knives and flail hammers are reversible. Generally, the machines with more of these blades - whether moving or fixed - the more efficient and faster the shredding.


Chipper-shredders usually include perforated metal plates or closely spaced steel bars located just beyond the shredding hammers at the discharge area of the machine. These screens or bars keep the garden waste in the shredding unit until it is small enough to pass through the holes or spaces. If you're shredding heavy, wet, or matted materials, a screen with large holes (or no screen at all) will permit most efficient shredding. If you want evenly fine-textured material, you can attach screens with 1-inch or 1/2-inch openings. Machines with screens are more likely to clog than those without screens. But those with screens are usually easy to clean out if they become jammed. On many models it's as easy as removing two or three hairpinlike fasteners. Standard screens have 1-inch openings. Smaller and larger screen openings are optional.

Check any chipper-shredder you're considering for ease of access to the shredding chamber. Jams occur no matter what kind of machine you have or how powerful it is. Easy access to the shredding chamber also makes it simpler to service the chipper knife and flail blade.

Clutch, Rotor and Engine

The Clutch. The clutch of a chipper-shredder is similar in function to a clutch found in a car or lawn tractor. It engages and disengages the rotor that holds the shredding and chipping blades. Two kinds of clutches are available: "idler lever" (or "throw") and "centrifugal."

Idler-lever clutches include a lever that you use to engage the shredding mechanism. They are relatively simple controls that give you more control over the chipping or shredding.

Centrifugal clutches engage or disengage automatically, depending on engine speed. For example, if the shredding assembly bogs down, a centrifugal clutch will automatically disengage, giving the engine time to increase power.

Machines without clutches are called "direct drive," which means that whenever the engine is operating, so is the entire shredding-chipping assembly. This means the user has less control, and these machines are harder to start because you must crank the engine and shredding-chipping mechanism at the same time. On the other hand, direct-drive machines are usually less expensive.

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