Brush-Clearing Head Evaluation
All but one of the heads held up well. The bottom housing of one head fractured when the head hit a rock abruptly (figure 6). A crack had developed from the small hole in the casting. This hole had been machined into the casting to help remove the pin used to hold the blades between the two housings. The hole is not required and will not be machined in any new heads.
Figure 6—A brush-clearing head that fractured during testing.
The fracture was a result of a machined hole in the casting.
The design flaw will be corrected.
Another problem discovered during the testing dealt with the head’s mount on the Stihl saw. Stihl has modified the shoulder height of the gear-head thrust plate on their new brush-clearing saws. Only a small amount of the head’s surface contacted the thrust plate. The head’s mounting surface cracked. Stihl has developed shims to fill the gap at the shoulder, which will eliminate the problem.
Comments From Evaluators—As part of the evaluation, the workers operating the brush-clearing saw were asked to critique the system.
Positive comments included:
Other comments include:
The new brush-clearing head with steel blades is effective for thinning young stands where workers must cut close to the ground (even in the ground) or around rocks. After some practice, the operator can become extremely efficient in clearing brush, trees, and other material with little or no downtime. The efficiency may make it practical to thin large areas of thick natural regeneration at an early stage rather than waiting for the stand to mature enough for chain saws to be useful. Clearing regeneration early may produce a stand that is more hospitable for wildlife and may promote tree growth. The clearing head has other uses, such as clearing trails or clearing undergrowth ahead of sawyers when constructing fireline.
The use of personal protective equipment cannot be overemphasized. In fact, from the test subjects’ comments, more equipment to protect the chest and groin should be specified and required to be worn. Additionally, the design of a larger or improved brush-clearing saw guard on the head may help prevent some of the debris from hitting the operator.
Two design flaws noted in field tests led to the fracture of one head. These flaws were determined by the manufacturer to be a direct result of the machining of the castings. The design flaws will be eliminated in the final design of future manufactured units.
Contact Pete Tagget at Fire Prevention Services (phone: 619–562–1058) for more information and availability of the brush-clearing head. At this printing, the head’s price had not been set.
Andy Trent is a project engineer at MTDC. He received his bachelor’s degree in mechanical engineering from Montana State University in 1989. Before coming to the center in 1996, he worked as a civilian engineer for the U.S. Department of the Navy. Andy works on projects in the reforestation and nurseries, forest health protection, and watershed, soil, and air programs.
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