How to Use: Brush cutters make the cut

Choosing the right brush cutter depends on factors such as worksite environment, terrain and the type of brush that needs cutting. The nature of the wood, for example, can affect your productivity, especially in different regions.

“Most regions have some form of invasive species and how it grows and cuts varies greatly,” says Mike Slattery, vice president of Fecon. “An oak tree in Wisconsin grows differently than one in Texas. In the West and Southwest fire is a great concern, as well as invasive species like pinion and juniper. Longer growing seasons in the South mean more vegetation to manage throughout the year.”

Bill Causey, an industrial salesman with Pioneer Machinery, which sells Prentice tractors, says softwoods such as pines, cedars or evergreens cut easier than hardwoods like hickories or oaks and older trees take longer to cut because their trunks thicken with age.

In heavy-duty land clearing applications, brush cutters are either dedicated tractor machines or attachments fitted to a skid steer, excavator, tractor or backhoe. “Mowers” refer to cutter attachments that handle grass, weeds and light brush under diameters of 4 inches. “Mulchers” include cutters that handle brush more than 4 inches in diameter and dedicated brush cutting tractors.

The role of brush cutters has evolved over time, fueled by changes in worksite management.

“Brush cutters were a long-time staple in forestry,” Causey says, “but in recent years, maintaining habitat has gained greater importance for construction applications. In the past, developers preferred to clear everything out. Now they realize maintaining some of the vegetation and mowing around it increases land value.”

A variety of cutters
Brush cutters come in two basic types, rotary (vertical shaft) and horizontal (drum). Each type cuts brush in a similar way, but excels in different applications.

“If you want a job to look like someone’s lawn, a horizontal drum cutter with a flail cuts best,” says Stan Brown, president of Brown Bear. “If you are not concerned about the finished product, you’d use a horizontal drum with fixed teeth. If there are no people, houses or other safety issues, and you don’t care what the result looks like, you cut with a vertical shaft machine.”

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The thickness of brush and terrain also factor into cutter choice. Justin Odegaard, attachment product representative for Bobcat, cites North Dakota as an example. “Up here we don’t have big trees but smaller brush, and we don’t want to remove trees if we can help it. The terrain is flat here, so something like a rotary cutter works well. When you get to the central East Coast where it’s rolling, a Brushcat or a flail works better there. A rotary on rolling ground ends up cutting dirt as much as cutting brush. Typically 2 to 3 inches is as close as you are going to get on flat ground with the rotary cutter.”

Rotary cutters resemble a lawnmower and come in several variations, but cut with blades that rotate parallel to the ground. They are simple to use and maintain, and cost 25 to 50 percent less than horizontal cutters. They are sometimes called “brush hogs.” “Rotary cutters are economical because they are not difficult to build and the components are relatively inexpensive,” Odegaard says. “The blade itself is your biggest wear item and it is easy to replace.”

But rotary cutters come with some drawbacks. They leave cut brush on the ground without processing it. Slattery says flails have a high travel speed and cut through brush 4 or 5 inches in diameter, but you sacrifice cutting quality compared to drum cutters.

The beat of the drum
Horizontal drum cutters consist of a set of blades or hammers attached to a steel drum. There are three basic types: flail, fixed tooth and ax blade.

The flail cutter breaks brush with sharp knives or blunt hammers. Flails have the longest belt, shaft and bearing life; cut faster and mulch material finer. They are also easy to maintain and their design allows them to give way when they pass over rocks.

Fixed-tooth cutters cut with blades attached to the outside of a drum, creating a unit with rigid teeth for cutting sturdier material below ground level. Some fixed-tooth cutters are made of carbide steel for chipping and handling large metal objects hidden in thick brush.

Fixed-tooth cutter teeth can last 300 to 400 hours, but the cutter only matches about 85 percent of a flail’s cutting speed. You get a shorter usage time with flail cutter knives because they need sharpening after 100 to 200 hours.

Ax blade cutters chop brush with sharpened knives. They cut grass, weeds or brush with diameters up to 6 inches and excel at chopping brush to fine mulch. To maintain efficiency, the blades need to be resharpened in the field two to three times per week.

“Sometimes a rotary ax is more productive with smaller material,” Causey says. “If you are working around buildings or if you want to ensure the safest environment, use a fixed ax head so you don’t throw material.”

Carrier machines and attachments
Some manufacturers produce dedicated tracked or rubber-tired tractors for brush cutting applications.

Rubber-tire tractors do little or no damage to roads and they excel in transport speed. “If you are going to travel down a road and then jump back into the woods, a rubber-tire machine can travel faster,” Slattery says. “That is also important if you are in a larger open space where the tree growth is spread apart. At that point, tree-to-tree time becomes critical and if they are far apart, faster travel speed is crucial.”

The low ground pressure of tracked tractors is a benefit on terrain that challenges rubber wheels. They also allow work on slopes with less risk of tipping over. “The wheeled carrier is nimble and moves through the woods with more speed,” says Lee Boyum, president of Jarraff and Geo-Boy. “The tracked carrier is a better option when conditions are muddy and wet, offering better traction and lower ground pressure.” Some tractors in the higher horsepower ranges have cutters that are power-take-off driven, using a driveshaft to deliver power from the tractor’s engine.

Some companies, such as Brown Bear, produce machines built for brush cutting and attach their own cutters to the machine. Others build tractors but use the attachments of another manufacturer. Geo-Boy, as an example, makes a rubber-wheel tractor, but uses Fecon drum cutters as an attachment.

Brush cutter attachments fit on carrier machines such as skid steers, excavators or backhoes. Although cutter attachments vary in design by carrier machine, their mechanics are the same.

The ideal carrier machine depends on the worksite’s brush. Skid-steer attachments, for example, effectively cut brush 4 to 6 inches in diameter. Although they cut larger debris, power and time become an issue.

“These mulchers can cut just about any size of wood. Even a skid-steer attachment can grind a 20-inch tree, it will just take longer,” Slattery says. “There are so many factors you have to think about with a skid steer such as the number of acres, the diameter of the trees onsite and how you want to grind them. Those variables start to factor into your production time. We try to tell people that if they want to buy a mulcher for a skid steer, look at hitting about one to two acres a day cutting 3- to 5-inch material.”

Excavator attachments are useful when you want to reach up onto steep slopes, dig down into ditches or need to selectively reach into areas. “National forests require a particular spacing between each tree to minimize fire-spreading,” Slattery says. “But you are not allowed to touch or damage the surrounding trees. In some cases an excavator can navigate in between those trees and reach rather than drive in between them, so it can minimize the disturbance area.”

Attachments reduce cost and time if you need to clear brush in a short period of time. “A lot of contractors have a skid steer or compact track loader already,” Odegaard says. “So instead of subbing that out, they can bring it back in-house and it will be on time because they are the ones coordinating the time frame of the work. That will potentially save them a lot of money over time.”

But Norm Beattie, product manager at Pro Mac Manufacturing, points out that attachment costs vary greatly depending on the carrier machine.

“There’s a considerable price difference between a skid steer compared to a mid-size excavator,” Beattie says. “You are talking $40,000 for a skid steer compared to $240,000 for a mid-size excavator. But the skid steer is not going to have the reach of an excavator. With a skid steer, you need to confine your work to a flat, level environment.”

Cost and hydraulic horsepower
An important cutter attachment spec is hydraulic horsepower. Hydraulic horsepower is the combination of hydraulic flow and pressure from the carrier machine to the attachment by way of a hydraulic pump. As the flow or pressure increases, so does the power transferred to the cutter. Attachments with a flow rate of 25 to 35 gallons per minute are a better match with carriers with engine power in the 80- to 100-horsepower range. The high engine horsepower of tractors can push hydraulic horsepower over a 100 gallon-per-minute rate. According to Jerry Sechler, vice president of sales for Loftness, hydraulic horsepower varies by design and manufacturer. “Many manufactures choose to keep the hydraulic horsepower level below the engine horsepower, using the relief valve system to limit the power to the head,” he says. “Other manufacturers will use a hydraulic system capable of higher horsepower than the engine. In this case the engine will pull down before the hydraulic system goes into relief mode. Ultimately, the power to the cutter head will be equal to the lower of these two numbers.”

The size of the brush also affects productivity. “If you are in the 25- to 35-gallon-per-minute flow range, you shouldn’t expect to cut more than 4- to 6-inch material,” Brown says. “If you are in the 35- to 40-gallon-per-minute range, you can expect to cut more than 8- to 10-inch material depending on the hardness and amount of the wood.”

In terms of cost, the smaller skid steer attachments that handle 1- to 2-inch-diameter material are the least expensive, ranging around $5,000 to $6,000. Larger drum attachments that handle 4- to 6-inch brush are about $20,000 to $25,000. Brush cutting tractors with an attachment can cost upwards of $100,000 to $300,000.


Quick Tips
Here are some safety and maintenance tips offered by the experts:

“Inspect and run clean air filters, check to see that the radiator and hydraulic coolers are clean and be sure these areas are free of debris. Remember that liquid leaks – especially engine and hydraulic oil – attract and hold dust and wood material, thus creating ideal conditions for fire.” – Mike Slattery, vice-president, Fecon

“Keep your blades sharp. Replace any blades you lose. Dull cutters and lost blades create an unbalanced cutter and cause vibration, which tears up the machinery.” – Stan Brown, president, Brown Bear

“Like any vehicle, brush cutters require periodic maintenance, which includes checking the air in the tires, the oil levels and replacing the air and oil filters. Always ensure the machine is properly greased before every work day.” – Lee Boyum, president, Jarraf Industries/Geo-Boy

“Maintain rotor rpm, allowing the speed and the inertia of the spinning rotor to help do the job. Constantly stalling the rotor and going over the relief valve settings can overheat any hydraulic system.” – Bill Schafer, product manager, Loftness


What about chippers and grinders?
Figuring out what to do with the material left over from brush cutting can create a dilemma, especially after cutting a large amount of brush. In some cases, the material is just left to biodegrade, but some jobs may require a clean site. This is where chippers and grinders come in. Although they process wood similar to brush cutters, chippers and grinders differ because the material needs to be cut before it is processed. Once processed, this material can be collected and sold for fuel or mulch.

Chippers process material with knives mounted on a disc or drum while grinders mulch with hammers in a mill. Tub grinders feed material into a bowl through an opening on top and horizontal grinders pull material into the hammer mill with an infeed conveyor. Tub grinders handle large-diameter pieces of material such as stumps and rootballs while horizontal grinders are better with longer pieces of raw material.

Chippers require clean wood with little rock and dirt to prevent knives from dulling quickly. Grinder hammers will tolerate some added debris.

“Establish what type of material your machine will process the majority of the time before you specify your machine,” says Mark Rieckhoff, environmental segment manager, Vermeer. “You may have to do some extra brush cutting to get the material to fit into some smaller machines.”

Many areas have a wood chip and fuel market that uses the waste products from chippers and grinders. Jerry Morey, marketing manager for Bandit, says a grinder can produce added revenue if put to good use. “If you have an established mulch market, you can produce $1 million a year easily per grinder,” he says. “Some of what you get from chippers will be mostly reground by a grinder. I know one guy who is doing between $18,000 to $20,000 worth of chips a working day, but everybody doesn’t do that.”


Source websites for more information
Brush Technology
www.brush-technology.com

Brown Bear
www.brownbearcorp.com

Jarraff Industries
www.jarraff.com

Pro Mac Manufacturing
www.promac.bc.ca

Loftness
www.loftness.com

Prentice
www.prenticeforestry.com

Gyro-Trac
www.gyrotrac.com

Sneller Machine
www.snellermachine.com

John Brown and Sons
www.brownbronto.com

Tigercat Industries
www.tigercat.com

Franklin Equipment
www.franklin-treefarmer.com

Fecon
www.fecon.com

Rowmec
www.rowmec.com

Kershaw Manufacturing
www.kershawusa.com