How to choose & use brushcutters – woodlot thinning

How to choose & use brushcutters – woodlot thinning – includes related information

Kenneth R. Boness

How To Choose & Use

Managing undesirable vegetation may seem a never-ending task if you’re a homeowner, grounds-keeper, woodlot owner, or forester. But if you’ve never enlisted the aid of a brushcutter, or haven’t tried one for a while, you may be amazed at how efficient today’s long-stemmed buzzsaws have become.

Streamlined and lightened through the use of space-age plastics and alloys, the modern brushcutter offers improved power output because of advances in the design of the engines and carburetors. The new models are being applied to a variety of tasks ranging from selectively thinning timber stands to clipping underwater weeds and cutting concrete. (Brushking makes an adaptor kit with a special blade hard enough to go through concrete.)

Options for controlling vegetation fall into three basic categories: natural, chemical, and mechanical. In many instances natural control – like the creation of a dense overstory to choke out brush – is simply not feasible. And you may wish to rule out chemical control if the treatment area is near a home, a body of water, or even a colony of bees. Cost, liability, and government regulations are other factors to consider in applying pesticides.

As for mechanical control, using hand tools is often unappealing because it is so labor-intensive. And cutting brush is not a chainsaw’s forte: kickbacks and broken chains are common, and stooping contributes to back strain.

Brushcutters are – or should be – the first choice for controlling unwanted vegetation. Offering advantages over all the alternatives, the modern brushcutter is rapidly growing in capability, adaptability, and popularity.

For one thing, unlike chemical treatments, brushcutting can be done year-round except in deep-snow country. In my neck of the woods (Wisconsin) in winter, I have experienced problems in getting a clear view of the stem at cutting height and dealing with ice buildup, which can cause a brushcutter’s blade to become unbalanced. As a result, I prefer to do most of my work in the fall after leaf drop. Visibility is enhanced, the weather is cooler, and summer chores are coming to an end. To cut brush along fencerows, I wait until the first dusting of snow, which makes foreign objects such as pieces of old barbed wire much easier to see and avoid.

Another factor to consider in timing your brushcutting is the health of the remaining stand. The downed stems, as they decompose, can allow disease organisms and harmful insects to multiply, damaging some tree species. Selecting the optimum season for thinning a stand can help avoid these plagues. Consult your local forester.

To help you select a brushcutter, I’ve examined their general characteristics and the specifics of 12 models, focusing on machines designed for cutting brush and saplings up to eight inches in diameter, which means those equipped with blades rather than line-trimmer heads.

Models intended to be used solely for clipping grass and weeds are known as trimmers. Practically all brushcutters can be converted into trimmers by substituting a line-trimmer attachment. Another term you may run across is clearing saws, which for all practical purposes can simply be described as the heavyweights of brushcutters.

Brushcutters have five readily recognizable components: handles, housing, guard, cutting attachment, and engine. The general arrangement of these components is, of necessity, standard, but features vary widely. For example, Tanaka and Shindaiwa each offer a model that features a backpack power unit.

Handles vary in design between brands and within product lines. Most, but not all, brushcutters have J or bicycle-type (also known as bullhorn) handlebars. Designed to give maximum control, the handles also act as a barrier, preventing the blade from contacting the operator in the event of a kickback.

Two handle elements you’ll want to look for are anti-vibration mounts, especially on the larger machines, and convenient, comfortable grips and controls. On all the units I’ve used, the handles can be swiveled forward (away from the operator). Some can be slid from side to side; others cannot. And you’ll find a few models that allow the handle clamp to be positioned at various points on the driveshaft housing.

As a general rule, brushcutters utilize straight driveshaft housings while the driveshaft housings of trimmers are curved, A straight housing allows the use of a stronger, rigid driveshaft and extends the blade farther from the operator’s feet.

One major difference between trimmers and brushcutters is the direction of rotation of the cutting head. Curved-shaft trimmers spin the cutting attachment in a clockwise direction. The straight shaft of brushcutters requires that a bevel gear be added in the drive head, which reverses the blade rotation. Consequently, should you want to switch from a curved- to a straight-shaft machine, you will need to alter your operating technique accordingly.

Every brushcutter also has a guard as standard equipment. Mounted on the driveshaft housing or the gearbox, this protective device should always be in place during operation. Even the small eight-inch blades can develop a maximum rim speed of over 225 miles per hour. I assure you that bits of wood as well as foreign particles will be flung indiscriminately. Everyone – operators and helpers – should have leather workboots, workgloves, and eye protection, preferably goggles.

Hardhats are necessary when cutting trees tall enough to inflict head wounds. Anyone not operating the brushcutter should stand back a distance equal to twice the height of the material being cut or 30 feet, whichever is greater.

Generally, blades are designed to cut wood, brush, heavy weeds, and grass. For convenience, regard this list as being in descending order in that blades can move down the list but not up. For example, brush blades will work on brush and weeds but labor horribly when put to wood. The difference lies in cutter design: brush blades cut by knifing, wood blades by sawing.

Another clue that will enable you to quickly determine a blade’s purpose is its construction material. Nonmetallic blades are meant for weeds or grass only. If used on brush, they will place an unreasonable load on the engine. Used for their intended purpose, they do a reasonable job.

Metal blades are divided into three groups based on tooth design and cutting action: knife, crosscut, and chainsaw chain. With metallic blades, the fewer the teeth, the lighter the intended purpose. A blade with three, four, or eight teeth is a grass, weed, or brush blade. Those intended for use on wood have 20 to 80 teeth, depending on design and diameter.

The knife blades are intended to cut nothing stouter than light brush and can be operator-sharpened. Blades of a crosscut design are similar to those used on a carpenter’s power saw or table saw. They have excellent stay-sharp capabilities but usually require professional sharpening.

The third category includes chain-saw-type blades, which can further be divided into those that use a pseudo chain pattern and those employing actual chainsaw cutters. The pseudo types appear to have chainsaw cutters when viewed from the side. They are a bit ticker than the crosscut blades, can be field-sharpened, and, like the others examined so far, are one-piece construction.

By contrast, the blades using actual chainsaw cutters are assembled from multiple components. Sabre Textron’s Sabre Tooth [TM] blade and the P.J. Blade from Big Pines Timber Company are two examples of blades made by rivetting individual chainsaw cutters to a steel disk. Saw Tech Industries’ Beaver Blade [TM] is constructed by welding two disks together so as to form a groove similar to that found on chainsaw bars. An actual length of saw chain is fitted into this groove and closed to create an endless loop.

Chainsaw cutter blades offer the same ease of sharpening as the pseudo blades, but they develop a significantly wider kerf, or width of cut. This is especially advantageous when cutting saplings three or more inches in diameter as blade pinching is minimized.

Choosing a blade diameter necessitates matching cutting depth capacity with the diameters of the stems you wish to cut. An eight-inch blade will not sever an eight-inch trunk even if you saw from both sides. Remember to deduct for the diameter of the gear head, which is at least 2 1/2 inches. Instead of an eight-inch blade yielding a cutting depth of four inches, you’ll get only 2 3/4 inches at most.

True, large stems can be felled by making an open notch and a back cut a la a chainsaw. But this is time-consuming and should not be the norm. You’ll enjoy being able to snip 90 percent of the stems without multiple cuts.

Each blade has a specific power requirement that corresponds to engine size expressed in cubic centimeters. My experience has been that a 25cc engine is sufficient for an eight-inch blade, but a nine-inch blade requires the power generated by a 30cc unit. Ten-inch blades need 35 to 40cc, and 12-inch blades require some extra snort, at least 50cc.

Let’s say you’ve selected blade type and diameter and correlated that with a particular range of engine sizes. What’s next? Comfort and ease of operation.

A few small brushcutters are equipped with a simple shoulder strap; the majority have harnesses instead. Harnesses have special features not commonly found on shoulder straps. Some have extra width across the shoulders to spread the load while others employ padded straps. All have hip pads to prevent chafe and wear on you and your clothing.

All harnesses have a quick-release system so that in case of emergency you can readily rid yourself of the brushcutter. Most systems use an integral pin worn near your solar plexus. One strap is attached to the pin, and the other three straps slip over it and are secured by a clip. Releasing the clip will allow you to shed the brushcutter and harness in a second or two.

Comfort is greatly enhanced by taking the time to balance your machine so that it will ride gracefully on your hip. The idea is to get the unit balanced so that you can let go and the cutting head will neither sink to the ground nor come up toward your face. When you’re working, the head will be right where you want it without constant effort on your part.

I tie a rope to a joist in my garage and adjust the rope so that a snap tied to one end hangs about chest high. I then slip the brushcutter’s ring into the snap and start adjusting. This is much easier than trying to locate the balance point with the machine on my hip.

One problem with balancing a brushcutter is that an empty or full fuel tank affects the unit’s behavior. It is customary to balance the machine with a full tank so that as the tank empties, the cutterhead will not have a tendency to float up toward the operator. Husqvarna has a new 49cc model, the 250RX, which introduces a forward-extending fuel tank to minimize balance change.

Throttle and ignition controls are standard in purpose and varied in design, but carburetors have greater differences. Most models still use a standard choke for cold starting, but the Olympyk 400B utilizes a positive primer, while the RedMax Reciprocator and Homelite ST-385 feature both a primer and a choke. A primer affords several advantages, but the one most apparent to the operator is the easy cold starts.

Maintenance of a brushcutter is relatively simple. The condition of the air filter, fuel filter, sparkplug, and starter rope should all be checked on a regular basis. Tighten all loose fasteners as soon as they are discovered, but check frequently the bolt or nut used to secure the blade. On straight-shaft machines, left-hand threads are used, which means that you will have to turn counterclockwise to tighten.

While you’re down there, check two other items. Make certain the gears are supplied with grease, and then visually inspect the blade for cracks or other defects. One-piece steel blades should also be checked by a single tap with a metal object: a cracked blade will not have a true ring. If any blade is found to be defective for any reason, discontinue using it at once.

If and how blades are to be sharpened depends on their construction and design. Nylon blades cannot be filed but can be dismounted and turned over, providing fresh cutting edges. A few nylon blades, such as one available from Sachs-Dolmar, can be trimmed with a scissors to expose new cutting edges. Be sure to follow the manufacturer’s instructions to avoid unbalancing and weakening the blade. Chainsaw-style blades can also be filed on the job, but most of us will need the services of a professional to maintain the edge on a crosscut blade.

Although brushcutter operation is something I enjoy, I had to make some adjustments as my experience grew. At first I would forget that a brushcutter’s blade will continue to spin after the throttle is released. There were times when I accidentally scarred trees that I didn’t want to cut. The easiest way to stop a blade is to hold it against the stem or stump that was just cut, but that was something I had to learn.

Cutting clumps such as alders posed another problem – I had trouble with the guard catching on the stumps as I went after more stems. Using a brushcutter requires a choreography more complicated than that of chainsawing, but once I’d worked out a system of moving around a clump, my production improved.

What I’ve presented so far is a brief summary of brushcutter capabilities, maintenance, and operation. In the second half of this article I’ll look at specific brands, models, and features. You may be amazed at the wide range of tasks these machines can tackle and how innovative features give each model a bit of individuality.


The process of determining which brushcutters best meet your needs requires identifying the tasks to be done and becoming familiar with brushcutter capabilities. Shindaiwa has published a booklet that is definitely worth reading. How To Buy a Trimmer without Getting Clipped is a commonsense approach to basic trimmer and brushcutter characteristics.

Once you have selected the blade(s) you’ll need, you’re about ready to make your final decision based on personal preferences of brand, features, dealer service, warranty, and price.

Following is a list of brushcutters and blades that I have examined and operated. The brushcutters are listed in alphabetical order so as to avoid inferring preference for any model.

Echo sent an SRM 3800, which at 37.4cc is the second largest model in its line. The company does not believe (and neither do I) in using a fast-idle throttle setting during startup. When you start this machine, the blade will not spin like a whirling dervish. Another unique feature is the multi-position blade guard which permits the use of blades of various diameters without having to purchase additional guards.

The Homelite ST-385 sports a compact powerhead assembly. My first impression of it as being too small soon changed as its 25cc engine was more than a match for all jobs up to and including cutting light brush. Featuring a primer and choke, it frequently started on the first pull.

Not meant for around-the-yard chores, the Husqvarna 165RX is an animal. Weighing in at 23 pounds, it is 10 pounds heavier than the Homelite ST-385, and the driveshaft housing is exactly three times the diameter of the Poulan/Weed Eater XT 125’s housing. The unit I received had Husky’s special Christmas-tree harvesting guard, which prevents kickback, allows the operator to “feel” trunk location, and prevents accidental contact of the blade with the ground. Powered by a gutsy 65cc engine, the 12-inch crosscut blade is carbide tipped and efficient.

Recently introduced at the top of the Jonsered lineup, the RS/51 deserves its position. Its displacement of 51cc affords power to spare for the heaviest of brushcutter chores. Features that pleased me were the easy-to-operate choke control, the multi-position possibilities of the handles, and one of the best harnesses on the market.

PHOTO : RedMax Reciprocator’s unique two blades cut with a scissoring action.

PHOTO : The Shindaiwa BP-35 is carried backpack-style and has a thick backpad for comfort.

PHOTO : The Echo SRM 3800 is used to clear out a suburban woodlot.

PHOTO : Using a Sachs-Dolmar,the author cuts small brush with a sweeping motion.

PHOTO : A properly balanced brushcutter like this Stihl FS 180 is a pleasure to operate. Note the quick-release harness system.

PHOTO : The Husqvarna 250RX clearing saw features a forward-mounted fuel tank for better weight distribution.

PHOTO : Brushcutters like this Poulan Pro 195 can easily be converted for grass-trimming duties.

A former professional logger and one-time retailer of brushcutters and chainsaws, Wisconsinite Ken Boness helps his brothers operate a tree farm and oversees maintenance and weed control on another tree farm.

COPYRIGHT 1990 American Forests

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