Brush-Clearing Head Evaluation, 0324-2336-MTDC

A TUFF KUTT head was purchased and tested at the Island Park Ranger District of the Targhee National Forest in Idaho. One TUFF KUTT head that was mounted on a Stihl FS 550 brush cutter failed during testing. The aluminum-alloy housing cracked (figure 3) and testing was stopped. Repeated attempts to contact the manufacturer were unsuccessful. Fortunately, we were able to contact the original inventor. He said that the manufacturer had focused on downsizing the original design to enter the consumer market. The inventor (now the director of technology for Fire Prevention Services, Inc.) agreed to produce a test run of the original design and allow the Forest Service to field test that design for 2 years. The test period ended December 31, 2002. This report summarizes the findings.

$Photo of a brush-clearing head fractured during testing.$
Figure 3—The alloy housing of this TUFF KUTT
brush-clearing head fractured during testing at Island Park, ID.

Design and Concept

The clearing head (figure 4) was designed to cut small brush around rocks and to cut below the ground without the need to sharpen the blades. The head’s cutting diameter with new blades is 11 inches. The head can cut up to 2-inch-diameter softwood trees, although test results show that the head should not be recommended for use on trees this large. The head works best on trees that are 1¼ inches in diameter and smaller, and for briars, grasses, and brush.

Photo of the original design for the brush-clearing head.

Figure 4—The original design of the brush-clearing
head used in Forest Service evaluation.

The clearing head is constructed of two lightweight aluminum-alloy castings housing three rotating (replaceable) steel blades mounted on steel pins. The saw’s mounting nut keeps the clearing head together. No other mechanical fasteners are needed. The clearing head weighs about 3 pounds with the blades. The head’s steel blades swing out as the head rotates, producing a well-balanced, easy-to-use cutting tool that can “carve” trees to cut them. The clearing head does not require that the tool be held tightly. The head should be pressed against the material being cut rather than swung into the material.

The main benefit of this brush-clearing head is its ability to strike the ground, rocks, and other hard debris repeatedly without loss of performance. The blades are designed to get shorter through wear without requiring sharpening. Cutting in rocks actually produces a slight curl at the end of the blade, enhancing the cutting action. Blade life depends on site conditions and the material that is being cut.

Recommended Brush-Clearing Saws

The clearing head’s manufacturer determined that brush-clearing saws manufactured by Stihl have the best power head and gearbox for use with the clearing head. No other manufacturer whose saws were tested could produce gearboxes that would hold up to the punishment of day-to-day use of the head.

Stihl models FS280K, FS350, and FS450 are recommended for use with the brush-clearing head (see table 2 for comparison). The FS 280K clearing saw is no longer manufactured, but this saw was able to stand up to all the testing to date. Such saws may still be available. The power output is satisfactory and the gearbox can withstand the punishment from the head. Other attributes that make the FS 280K a good choice include a long shaft length (35 inches), light weight (17 pounds), and adjustable handlebars. In addition, the saw rapidly recovers its cutting speed after it has slowed while cutting material.

Stihl brush-clearing saw models
	FS 350	FS 280K	FS 450
Weight (pounds)	15.4	17	17.4
Displacement (cubic centimeters)	36.3	39	44.3
Fuel capacity (pints)	1.35	1	1.43
Maximum engine speed (revolutions per minute)	12,300	12,500	12,500
Tube wall thickness (inches)	0.0625	0.0625	Heavier than 0.0625
Shaft length (inches)	36 7/8	35	31 5/8

Because the FS 280K is no longer readily available, the Stihl FS 350 is a good substitute. It is similar to the FS 280K, but has a slightly smaller engine and is about 1½ pounds lighter. The FS 450 would also work with the brush-clearing head, but it is about 2 pounds heavier than the FS 280K and has a much shorter shaft, which may make the saw harder to maneuver.

Stihl makes another brush-clearing saw, the FS 550. This saw was not tested because it was considered too large, had a shaft that was too short, was heavy, and was too expensive.

Several minor modifications to the saw’s guard are needed before the brush-clearing head can be mounted on the Stihl saws. Two gussets or “ears” must be removed from the guard so it can be mounted farther back from the end of the shaft. Also, a small piece should be removed from the lower corner of the guard, tapering back about 1 inch. This allows the clearing head blades to rotate without hitting the extreme outer corner of the guard. The modifications will be detailed in the clearing head operator’s manual supplied by the manufacturer.