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Prevailing Torque
Certain applications (such as self-tapping fasteners or fasteners into locking helical inserts) require compensation for the
prevailing torque of a fastener in the final torque of the rundown. This can be accomplished using the ‘Calc Prevail
Torque’ feature in an angle control parameter. For easy identification, angle control parameters using the prevailing
torque option have a purple outline on the parameter blocks.
The desired compensation can be accomplished by programming a 2-step rundown, starting with an angle control
parameter (with the prevailing torque calculation enabled), followed by a torque control parameter.
In the example shown above, the fastener is rotated 540 degrees in step 1, during the last 405 degrees (75%) the
prevailing torque is monitored and the average value reported. Step 2 is then performed to a target of 10 inlb, but the
actual applied torque is the final torque of 10.01 inlb plus the 3.21 inlb calculated for a total of 13.22 inlb.
The torque displayed on the ‘Run Tool’ screen will be just the clamping torque as targeted in the torque control
parameter programmed to the final step. To see a breakdown of the prevailing torque and the total applied torque,
view the rundown data on the ‘Data’ screen of the controller.
Utilizing this method will calculate the prevailing torque for each fastener eliminating the need to determine an average
value for all fasteners and then using a standard torque profile only with a larger target.
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