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20 Cordless Impact Wrench Operator's Manual
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.
a. Voltage:
When the discharge margin is reached, voltage decreases and tightening
torque is lowered.
b. 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. 16)
c. Diameter of bolt:
The tightening torque differs with the diameter of the bolt as shown in
Fig. 16. Generally a larger diameter bolt requires larger tightening torque.
d. 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 workplace
through which the bolts are to be tightened. When the bolt and nut turn
together, torque is greatly reduced.
e. Using optional parts:
The tightening torque is reduced a little when an extension bar, universal
joint or long sockets are used.
f. Clearance of the socket:
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.
g. Tightening torque varies, depending on the battery’s charge level Fig. 18
shows an example of the relationship between tightening torque and the
number of tightenings. As shown, tightening torque gradually weakens with
the increase in the number of tightenings. In particular, as the torque
decreases very close to the complete discharge (“a” margin in graph), the
unit’s impact weakens, the number of time impacts declines and tightening
torque drops off abruptly. If this occurs, check torque level, then recharge the
battery if necessary.
OPERATION CAUTIONS (CONTINUED):
Operation