Stihl HT Instruction Manual page 11

Reactive Forces
WARNING
Reactive forces may occur any time the
chain is rotating.The force used to cut
wood can be reversed and work against
the operator. If the rotating chain is
suddenly stopped by contact with any
solid object such as a branch or is
pinched, the reactive forces may occur
instantly. These reactive forces may
result in loss of control, which, in turn,
may cause personal injury. An
understanding of the causes of these
reactive forces may help you avoid the
element of surprise and loss of control.
Because of the design of the pole
pruner, the reactive forces experienced
when working with it are generally not as
severe as those encountered with a
chain saw. Nevertheless, you should
always maintain a proper grip and good
footing to control the power tool when
you experience such forces.
The most common reactive forces are:
kickback,
–
pushback,
–
pull-in.
–
Kickback
Kickback may occur when the moving
saw chain near the upper quadrant of
the bar nose contacts a solid object or is
pinched.
HT
The reaction of the cutting force of the
chain causes a rotational force on the
pole pruner in the direction opposite to
the chain movement. This may cause
the bar to move upward.
To Avoid Kickback
The best protection from kickback is to
avoid kickback situations:
1. Be aware of the location of the guide
bar nose at all times
2. Never let the nose of the guide bar
contact any object. Do not cut limbs
with the nose of the guide bar. Be
especially careful near wire fences
and when cutting small, tough
limbs, which may easily catch the
chain.
3. Cut only one limb at a time.
A = Pull-in
Pull-in occurs when the chain on the
bottom of the bar is suddenly stopped
when it is pinched, caught or encounters
a foreign object in the wood. The
reaction of the chain pulls the saw
forward.
Pull-in frequently occurs when the chain
is not rotating at full speed before it
contacts the wood.
To Avoid Pull-in
1. Be alert to forces or situations that
may cause material to pinch the
chain at the bottom of the bar.
2. Always start a cut with the chain
rotating at full speed.
B = Pushback
Pushback occurs when the chain on the
top of the bar is suddenly stopped when
it is pinched, caught or encounters a
foreign object in the wood. The reaction
of the chain may drive the saw rapidly
straight back toward the operator.
Pushback frequently occurs when the
top of the bar is used for cutting.
To Avoid Pushback
1. Be alert to forces or situations that
may cause material to pinch the
chain at the top of the bar.
2. Do not cut more than one limb at a
A
time.
3. Do not twist the bar when
withdrawing it from an underbuck
cut because the chain can pinch.
English
B
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