Hitachi WH 9 DMR [9/74] English
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Hitachi WH 9 DMR [9/74] English

Hitachi WH 9 DMR [9/74] English
English
8
CAUTION
Applying the impact driver for too long tightens the
screw too much and can break it.
Tightening a screw with the impact driver at an angle
to that screw can damage the head of the screw and
the proper force will not be transmitted to the screw.
Tighten with this impact driver lined up straight with
the screw.
OPERATIONAL CAUTIONS
1. Resting the unit after continuous work
After use for continuous bolt-tightening work, rest
the unit for 15 minutes or so when replacing the
battery. The temperature of the motor, switch, etc.,
will rise if the work is started again immediately after
battery replacement, eventually resulting in burnout.
NOTE
Do not touch the protector, as it gets very hot during
continuous work.
2. Cautions on use of the speed control switch
This switch has a built-in, electronic circuit which
steplessly varies the rotation speed. Consequently,
when the switch trigger is pulled only slightly (low
speed rotation) and the motor is stopped while
continuously driving in screws, the components of the
electronic circuit parts may overheat and be damaged.
3. Use a tightening time suitable for the screw
The appropriate torque for a screw differs according to
the material and size of the screw, and the material
being screwed etc., so please use a tightening time
suitable for the screw. In particular, if a long tightening
time is used in the case of screws smaller than M8, there
is a danger of the screw breaking, so please confirm the
tightening time and the tightening torque beforehand.
4. Work at a tightening torque suitable for the bolt
under impact
The optimum tightening torque for nuts or bolts differs
with material and size of the nuts or bolts. An
excessively large tightening torque for a small bolt
may stretch or break the bolt. The tightening torque
increases in proportion to the operation time. Use
the correct operating time for the bolt.
5. Holding the tool
Hold the impact wrench firmly with both hands. In
this case hold the wrench in line with the bolt.
It is not necessary to push the wrench very hard.
Hold the wrench with a force just sufficient to
counteract the impact force.
6. Confirm the tightening torque
The following factors contribute to a reduction of the
tightening torque. So confirm the actual tightening
torque needed by screwing up some bolts before the
job with a hand torque wrench. Factors affecting the
tightening torque are as follows.
(1) Voltage
When the discharge margin is reached, voltage
decreases and tightening torque is lowered.
(2) Operating time
The tightening torque increases when the operating
time increases. But the tightening torque does not
increase above a certain value even if the tool is
driven for a long time.
(3) Diameter of bolt
The tightening torque differs with the diameter of the
bolt. Generally a larger diameter bolt requires larger
tightening torque.
(4) Tightening conditions
The tightening torque differs according to the torque
ratio; class, and length of bolts even when bolts with
the same size threads are used. The tightening torque
also differs according to the condition of the surface
of workpiece through which the bolts are to be
tightened. When the bolt and nut turn together, torque
is greatly reduced.
(5) Using optional parts (Impact wrench)
The tightening torque is reduced a little when an
extension bar, universal joint or a long socket is used.
(6) Clearance of the socket (Impact wrench)
A worn or deformed hex. or a square-holed socket
will not give an adequate tightness to the fitting
between the nut or anvil, consequently resulting in
loss of tightening torque.
Using an improper socket which does not match to
the bolt will result in an insufficient tightening torque.
MAINTENANCE AND INSPECTION
1. Inspecting the driver bit (Impact driver)
Using a broken bit or one with a worn out tip is
dangerous because the bit can slip. Replace it.
2. Inspecting the socket (Impact wrench)
A worn or deformed hex. or a square-holed socket will
not give an adequate tightness to the fitting between
the nut or anvil, consequently resulting in loss of
tightening torque. Pay attention to wear of a socket
holes periodically, and replace with a new one if needed.
3. Inspecting the mounting screws
Regularly inspect all mounting screws and ensure
that they are properly tightened. Should any of the
screws be loose, retighten them immediately. Failure
to do so may result in serious hazard.
4. Maintenance of the motor
The motor unit winding is the very “heart” of the
power tool.
Exercise due care to ensure the winding does not
become damaged and/or wet with oil or water.
5. Inspecting the carbon brushes (Fig. 13)
The motor employs carbon brushes which are
consumable parts. Since and excessively worn carbon
brush can result in motor trouble, replace the carbon
brush with new ones when it becomes worn to or
near the “wear limit” P. In addition, always keep
carbon brushes clean and ensure that they slide freely
within the brush holders.
NOTE
When replacing the carbon brush with a new one, be
sure to use the Hitachi Carbon Brush Code No. 999054.
6. Replacing carbon brushes
Take out the carbon brush by first removing the
brush cap and then hooking the protrusion of the
carbon brush R with a slotted head screw driver,
etc., as shown in Fig. 15.
When installing the carbon brush, choose the direction
so that the nail of the carbon brush Q agrees with the
contact portion outside the brush tube S. Then push
it in with a finger as illustrated in Fig. 16. Lastly,
install the brush cap.

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