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6. Confirm the tightening torque
The following factors contribute to a reduction of the tightening torque. So con-
firm 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) Line voltage:
The tightening torque decreases when the line voltage becomes low. (See
Fig. 4)
(2) Operating time:
The tightening torque increases when the operating time increases. But the tight-
ening torque does not increase above a certain value even if the tool is driven
for a long time. (See Fig. 4)
(3) Diameter of bolt:
The tightening torque differs with the diameter of the bolt as shown in Fig. 4.
Generally a larger diameter bolt has a 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 metal through which the
bolts are to be tightened.
(5) Using optional parts:
The tightening torque is reduced a little when an extension bar, universal joint
or a long socket is used.
(6) Clearance of the socket:
A worn or deformed hex. or a square-holed socket will not give an adequate tight-
ness to the fitting between the nut or anvil, consequently resulting in loss of tight-
ening torque.
Using an improper socket which does not match to the bolt will result in an insuf-
ficient tightening torque. Matching socket and bolt sizes are shown in Table 1.
English
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