Reaction Forces - Echo SRM-225 Operator's Manual

OPERATION

Reaction Forces

The cutting attachment will continue to rotate even after the throttle is released, maintain control
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of the unit until it has come to a complete stop.
Blade thrust may occur when the spinning blade contacts an object that it does not immediately
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cut. Following proper cutting techniques will prevent blade thrust.
Blade thrust can be violent enough to cause the unit and/or operator to be propelled in any
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direction, and possibly lose control of the unit.
Blade thrust can occur without warning if the blade snags, stalls or binds.
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Blade thrust is more likely to occur in areas where it is difficult to see the material being cut.
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Push or Pull - Kickout
During normal use, operating a brushcutter with a circular metal blade can produce sudden strong reaction
forces that are difficult to control. Strong reaction forces can cause a loss of balance or loss of control of the
equipment, resulting in serious injury to operator and bystanders.
Understanding what causes these reactive forces may help you to avoid them, and can help you to maintain
control of the equipment if you experience a sudden reaction during cutting. Reactive forces occur when the
force being applied by the cutting teeth of a blade meet resistance, and some of the cutting force is directed
back toward the equipment. The greater the cutting force or the amount of resistance, the greater the
reactive force.
Push and Pull Forces
Push and pull forces are reactive forces that push the equipment directly toward the operator, or
that pull the equipment directly away from the operator. These forces are the result of cutting on
the sides of the blade. The direction of the force depends on the side of the blade being used,
and the direction of blade rotation at the point of contact. The reactive force is in the opposite
direction of blade rotation at the contact point, regardless of where the contact is being made.
These types of reactive forces are also called "Blade Thrust."
As shown in the illustration, a blade turning counterclockwise will cause the equipment to pull
away from the operator if the point of cutting resistance is on the left side of the blade. If the
point of cutting resistance is on the right side of the blade, the equipment will push back
toward the operator. In both examples, the reactive force is in the opposite direction of blade
rotation at the contact point where resistance occurs.
Kickout
Kickout is also a reactive force caused by resistance to cutting, but the direction of blade
thrust is lateral (to the left or right of the blade), instead of forward or back toward the
operator. In most cases, Push, Pull, and Kickout can be reduced or eliminated by:
• Using the correct blade for the cutting job
• Using properly sharpened blades
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SRM-225
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