A mechanic is securing a critical structural joint using a drilled bolt, a castellated nut, and a cotter pin. Arrange the following steps in the correct chronological order to properly install and lock this fastener assembly according to standard mechanical practices.
- 1Clean and inspect the threads of both the bolt and the castellated nut for any damage or debris.
- 2Thread the castellated nut onto the bolt and tighten it to the manufacturer's specified initial torque value.
- 3Visually check the alignment between the slots on the castellated nut and the cross-drilled hole in the bolt shank.
- 4Continue tightening the nut slightly (never loosening it) until a slot perfectly aligns with the drilled hole.
- 5Insert the cotter pin through the aligned assembly and bend the prongs to positively lock the nut in place.
Answer
The correct sequence is to first clean and inspect the components, apply the initial baseline torque, check the hole alignment, tighten the nut further if necessary to align the slots, and finally install and secure the cotter pin.
Proper installation of a castellated nut and cotter pin requires a strict sequence. First, components must be cleaned for accurate torque application. Second, the nut is tightened to the specified baseline torque to achieve the necessary joint tension. Third, alignment is checked. Fourth, because the nut's slots and the bolt's drilled hole rarely align perfectly at the exact baseline torque, standard mechanical practice dictates tightening the nut slightly further until alignment is achieved; backing off the nut is strictly prohibited as it would compromise the minimum required clamping force. Finally, the cotter pin is inserted and its prongs are bent to provide a positive mechanical lock against vibration.
Step-by-Step Solution
Key Concept
Proper installation sequence and torque application for positive-locking fasteners (castellated nuts and cotter pins).