210 ONE MAN HOLE DIGGER, FORM GOM-1061-1189, VERSION 2.0, AUTHORIZATION: DVR, PAGE: 15
becomes fully disengaged with no horsepower and
torque is being transmitted to the auger. In the slipping
mode, a centrifugal clutch still transmits a specific
amount of horsepower and torque to the auger. This
specific amount of horsepower and torque directly
proportional to many factors including: the mechanical
condition of the centrifugal clutch assembly and the
rotational speed of the centrifugal clutch assembly
when the initial slippage occurs. The response time for
the centrifugal clutch assembly to react to an overload
condition is directly proportional to its rotational speed.
The higher the rotational speed (RPM) of the
centrifugal clutch at the time of overload, the greater
amount of time it requires to react and actually slip.
This phenomenon is inherent with all centrifugal clutch
assemblies. It is also inherent with all powered
equipment incorporating such a device.
STRIKING BURIED OBSTRUCTIONS SUCH AS
TREE ROOTS, ROCKS AND OTHER DEBRIS AT
ANY SPECIFIC ENGINE OPERATING SPEED CAN
CAUSE THE HOLE DIGGER TO TRANSMIT
REACTIONARY TYPE "IMPACT" LOADS TO THE
OPERATOR. THESE TYPES OF LOADS ARE
CHARACTERIZED BY A SHARP, PULSATING
MOVEMENT OF THE HOLE DIGGER IN A
COUNTERCLOCKWISE DIRECTION (AS VIEWED
BY THE OPERATOR). SUCH LOADS CAN LEAD TO
THE LOSS OF OPERATOR CONTROL AND RESULT
IN PERSONAL INJURY. THE OPERATIONAL
EFFECTS ARE ALIKE TO THAT OF UTILIZING A
COMMON ELECTRIC DRILL AND OTHER,
ROTATION TYPE, POWERED EQUIPMENT. THE
RELATED PHENOMENON IS INHERENT WITH ALL
SUCH TYPES OF ROTATION TYPE, POWERED
EQUIPMENT AND IS TERMED AS KICKBACK.
UNDERSTANDING KICKBACK.
The operation of the Hole Digger involves engine
torque being transmitted and multiplied by the
transmission to the auger. The energy is then used to
dig holes. But to every force (action), there is always a
reaction force in the opposite direction. Thus, if the
auger contacts a buried obstruction, the operator will
feel the left side of the handle of the Hole Digger being
"thrusted" toward him. This "thrusting" force
experienced by the operator is called kickback. The
speed that the handle moves (and magnitude of the
resulting impact force) is directly proportional to the
amount/speed of the kickback force experienced by
the operator. The torque and kickback generated by
the digging process is inherent with a portable, one
man Hole Digger of this type. The operational effects
are alike to that of utilizing a common, electric drill and
other, rotation type, powered tools.
MINIMIZING KICKBACK FROM AN OPERATIONAL
STANDPOINT.
The operator should keep the left side of the handle as
close to his body (left hip and leg areas) as possible to
minimize machine "kickback" when a buried
obstruction is encountered by the auger. Assume
operating positions that allow exercising reactive "body
english" against the torque sensation created by the
digging process. Keep upper arms as close to the
upper body as possible to maximize mechanical
leverage. An operator should position his back as
vertical as possible by bending the legs as required
during the digging process. Positioning the left foot
ahead of the right foot at a confortable distance will
enhance proper body position. Maintaining proper
operating position is one of the most IMPORTANT and
EFFECTIVE procedures for controlling kickback.
Improper operating positions only aggrevate the effects
of kickback upon the operator. FIGURE 8 depicts a
proper operator position. FIGURE 9 depicts an
improper operator position.
FIGURE 8
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