Tightening Torque Inspection Prior To Operation; Tightening Torque Variation - Hitachi WH 14DMR Technical Data And Service Manual

8-2. Tightening Torque Inspection Prior to Operation

As described and shown in Para.7-3-3, the output tightening torque of which the Models WH 14DMR,
WH 18DMR, WR 14DMR and WR 18DMR are capable in excess of the rated tightening torque of certain bolts
and screws. Accordingly, if the tightening time is prolonged for such bolts and screws, it could cause damage to
their threads or, in the worst case, cause them to be sheared off. (This phenomenon is common to all existing
impact drivers.) Particularly when tightening M6 (1/4") or smaller screws, tightening time must be kept extremely
short: 0.5 seconds or less. The customer should be advised to carry out several screw tightening operations and
adjust the tightening time as necessary by measuring the tightening torque with an appropriate torque wrench or
driver before commencing continuous operation.

8-3. Tightening Torque Variation

The tightening torque of the cordless impact driver or wrench may vary slightly in accordance with the factors
described below. Salespersons are requested to advise the customer to confirm that appropriate tightening
torque is obtained by measuring the torque with an appropriate torque wrench or torque driver at the beginning of
the tightening operations, and as necessary during the tightening operations. In addition, the torque values
shown in Para. 7-3-2 above are useful as a handy reference, and may be utilized as tentative standards.
(1) Voltage of battery
Tightening torque is affected by the voltage output of the battery. For example, the relationship between
tightening torque and the number of M16 x 55 mm (5/8" x 2-5/32") F10T bolts tightened is shown in Fig. 6
below. As can be seen in the graph, tightening torque decreases as the number of bolts tightened increases.
This phenomenon is caused by the decline in voltage output of the battery due to the increasing number of
bolts tightened. In particular, the tightening torque decreases rapidly just before the battery is fully discharged
(range "a" in the graph). As this phenomenon is an inherent drawback in any cordless impact driver,
salespersons are requested to ensure that the customer is fully aware of and understands this characteristic.
Model WR 14DMR
Fig. 6
--- 25 ---