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the powerful 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 like a log or branch or is
pinched, there active forces may occur
instantly. These reactive forces may
result in loss of control which may, in
turn, cause serious or fatal injury. An
understanding of the causes of these
reactive forces may help you avoid loss
of control.
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.
14
The reaction of the cutting force of the
chain causes a rotational force on the
chainsaw in the direction opposite to the
chain movement. This may fling the bar
up and back in an uncontrolled arc
mainly in the plane of the bar. Under
some cutting circumstances the bar
moves towards the operator, who may
suffer severe or fatal injury.
Kickback may occur, for example,
when the chain near the upper quadrant
of the bar nose contacts the wood or is
pinched during limbing or when it is
incorrectly used to begin a plunge or
boring cut.
The greater the force of the kickback
reaction, the more difficult it becomes for
the operator to control the saw. Many
factors influence the occurrence and
force of the kickback reaction. These
include chain speed, the speed at which
the bar and chain contact the object, the
angle of contact, the condition of the
chain and other factors.
The type of bar and saw chain you use
is an important factor in the occurrence
and force of the kickback reaction. Some
STIHL bar and chain types are designed
to reduce kickback forces. STIHL
recommends the use of reduced
kickback bars and low kickback chains.
ANSI B 175.1-2000 chainsaw
kickback standard
Section 5.11 of ANSI standard
B 175.1-2000, sets certain performance
and design criteria related to chainsaw
kickback.
To comply with section 5.11 of ANSI
B 175.1-2000:
MS 440, MS 440 W, MS 440 C
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