Wood Chippers by Mark Henricks

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Wood chippers are used to reduce dead wood—felled trees, retired utility poles, brush and other green waste. The process is fairly straightforward: wood goes in and chips fly out. But like the machines that create them, not all chips are created equal. Some can be profitable, others merely problematic. As far as chipper manufacturers are concerned, the desired end defines the right chipper for the job.

A chipping chore could entail residential landscaping and tree trimming, forest maintenance, clearance for power lines or land development. Three standard chipper designs are primed for the task. The high-speed rotor chipper — a.k.a. the “chuck and duck” — is a non-hydraulically-fed machine that has lost much of its luster to the safer, hydraulically-fed disc chippers first introduced by Morbark, Inc. in the late 1970s. Drum chippers have come into favor during the last decade.

“The choice depends on the products you’re processing,” says Greg Millis, governmental sales director for Morbark, which manufactures a range of chippers from the small, trailer-mounted drum-styles to giant, stationary disc chippers. “If I’m a contractor selling clean chips to a paper mill, I wouldn’t think about using a drum chipper,” he says. “If I’m a big land clearing contractor, though, I wouldn’t need a disc chipper.”

Disc chippers allow operators to size their chips, often a prerequisite to supplying spec.-happy pulp and paper mills, or landscaping companies that will color the chips for sale as decorative mulch, so-called “yuppie bark.” Disc chippers are considerably larger and heavier machines than their counterpart and, as a result, can be less maneuverable and far pricier. The upside is that they are capable of dispensing with the whole tree.

“Disc chippers are basically a Cuisinart on steroids,” says Dave Benton, marketing and advertising manager for Peterson. Like Morbark, Peterson offers a line of disc chippers that can be packaged as all-in-one solutions for large-scale tree operations catering to the pulp industry. Rather than waste tree tops, limbs and bark left over from traditional, manual preparation of trees for chipping, disc chippers like the Peterson 5000G Delimber/Debarker/Chipper incorporate various flail-type trimming devices to automatically sheer off and separate bark and other unwanted materials that cause pulp and paper mills to cry foul. The clean stem, or bole, is then fed through the chipper.

“Those smaller limbs and bark, the byproduct that is pushed out of the machine, can then be valuable for use as a ‘hog fuel,’” says Benton, referring to chips used for boiler fuel at pulp or biomass plants. With skyrocketing natural gas prices, the industry is seeing a shift back toward utilizing the waste chippers to create a fuel source.

Since chips for boiler fuel need not be free of bark or uniform in size, a drum chipper is equally well suited to the task. “Unfortunately,” says Mike Byram, senior director of Vermeer’s Environmental Business Segment, “we usually just hear customers say, ‘I take it to the landfill.’” To supply bio-fuel and reap a profit, mass quantities of chips are needed. Drum chippers, which typically cater to small-scale landscaping and land-clearing operations, rarely produce sufficient quantities. Still, manufacturers see future growth in this market as fuel prices continue to rise and more landfills invoke bans on dumping wood.

As it is, the drum chipper manufacturers interviewed for this article—Vermeer, Morbark, Bandit and Dynamic—focus more on improving the standard functions of their machines than worrying about the aforementioned fringe benefits, namely chips as fuel or mulch. According to Tom Gross, president of Dynamic Mfg. Corp., “Chippers are primarily used as the first means of breakdown, to take trees cut down from land clearing jobs, yard trimmings, to reduce the volume that may end up in a landfill.”

All hand-fed drum chippers function similarly. “To start with,” Byram explains, “you have the in-feed table. The material, once it’s on the table, is fed into the drum by hydraulic feed rollers. These act to pull the material in as well as to resist self-feeding. The old-style feeds, without rollers, would actually suck that material in. So it’s a more controlled process now.” The material is then chipped by the blades on the drum, after which a series of paddles accelerate the chips to blast them out the chute.

On contract jobs, where time is money, productivity and chipping capacity are major concerns. Dynamic Mfg. Corp. has developed and patented a unique Cone-Head drum design that orients material to its staggered knife system for more efficient cuts. “With a 12 inch log at 250 horsepower, a traditional drum machine might only chip a foot to a foot and a half before the feed system stops,” says Gross. “With the Cone-Head, our chippers can chip two to two and a half feet.”

As the hydraulic feed system is the heart of a chipper’s innards, it is also a focal point for innovations. Vermeer is another manufacturer that has reinterpreted certain standard chipper features. “Most chippers have some sort of feed system, based on engine rpm, that controls the feed speed,” says Byram. “With our Smart Feed control system, if a material won’t go in, the machine will back it up different distances each time, three times, to get the material to rotate and go back in.” This helps take the operator running the top bar out of the equation.

Reducing manual-labor costs and protecting chipper operators are not merely secondary goals to manufacturing efficient, high-capacity machines durable enough to stand both the rigors of their inherent engine vibrations and the rough terrain they are often pulled through. Horror stories abound of chipper operators being caught up in tree limps and dragged into the blades, to lose a pinky or, worse, a head. Safety, not surprisingly, is of paramount concern to manufacturers.

While all chipper designs incorporate some sort of emergency shut-down lever, Vermeer has redesigned and relocated its stop bar so that an operator who is being inadvertently dragged onto an in-feed table will automatically trip the bar, rather than have to actively grasp for it to shut down the chipper’s feed system.

Such dire situations are rare, but buyers are nonetheless wise to evaluate the safety features just as they would productivity, quality and durability and, lest we forget, its maintenance needs. Like all heavy machinery, chippers will eventually need servicing. As downtime equals money, users must ensure that a dealer network is close by.

Of course, preventative maintenance—checking fluids, cleaning filters, maintaining sharp knives, greasing moving parts—can reduce downtime considerably. A machine is only as good as the person operating it.