ABSTRACT
As an example (see Fig. 12), the valve casting was machined around the hole for bolt 5, while the surface condition around the hole for bolt 10 was "as-cast" or "not machined." Both bolts were the same size (5/16"-18, SAE Grade 2). As a result, the underhead friction conditions for the two bolts are significantly different, requiring different sets of control parameters to achieve the same level of fastener preload. Later audit of bolt tensions produced by a torque-only control method (Fig. 13) clearly demonstrates the fact that a significantly smaller preload was achieved in bolt 10 than in bolt 5 of the same size. Both bolts were tightened to the same torque using a 10-spindle nut runner with DC brushless motors.
