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3. Tightening torque
Refer to Fig. 17, 18, 19 and 20 for the tightening torque of bolts (according to size),
under the conditions shown in Fig. 21. Please use this example as a general reference,
as tightening torque will vary according to tightening conditions.
NOTE:
⅜ If a long striking time is used, screws will be strongly tightened. This may cause the
screw to break, or may damage the end of the bit.
⅜ If the unit is held at an angle to the screw being tightened, the head of the screw may
be damaged, or the specified torque may not be transmitted to the screw. Always keep
the unit and the screw being tightened in a straight line.
4. 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 5/16” (8 mm), there is a danger of the screw breaking, so please confirm the
tightening time and the tightening torque beforehand.
5. 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 proportionate to the operaton time.
Use the correct operating time for the bolt.
6. 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.
7. 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.
(See Fig. 17, 18, 19 and 20)
(3) Diameter of bolt
The tightening torque differs with the diameter of the bolt as shown in Fig. 17, 18, 19
and 20. 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 (WR12DM2, WR9DM2)
The tightening torque is reduced a little when an extension bar, universal joint or a
long socket is used.