Safetying Methods – Part Three

in Aircraft Materials Processes and Hardware

General Safety Wiring Rules

When using the safety wire method of safetying, the following general rules should be followed:


  1. A pigtail of 1⁄4 to 1⁄2 inch (three to six twists) should be made at the end of the wiring. This pigtail must be bent back or under to prevent it from becoming a snag.
  2. The safety wire must be new upon each application.
  3. When castellated nuts are to be secured with safety wire, tighten the nut to the low side of the selected torque range, unless otherwise specified, and if necessary, continue tightening until a slot aligns with the hole.
  4. All safety wires must be tight after installation, but not under such tension that normal handling or vibration will break the wire.
  5. The wire must be applied so that all pull exerted by the wire tends to tighten the nut.
  6. Twists should be tight and even, and the wire between the nuts as taut as possible without overtwisting.
  7. The safety wire should always be installed and twisted so that the loop around the head stays down and does not tend to come up over the bolt head, causing a slack loop.

Cotter Pin Safetying

Cotter pin installation is shown in Figure 5-76. Castellated nuts are used with bolts that have been drilled for cotter pins.

Figure 5-76. Cotter pin installations.

Figure 5-76. Cotter pin installations.

The cotter pin should fit neatly into the hole, with very little sideplay. The following general rules apply to cotter pin safetying:

  1. The prong bent over the bolt end should not extend beyond the bolt diameter. (Cut it off if necessary.)
  2. The prong bent down should not rest against the surface of the washer. (Again, cut it off if necessary.)
  3. If the optional wraparound method is used, the prongs should not extend outward from the sides of the nut.
  4. All prongs should be bent over a reasonable radius. Sharp angled bends invite breakage. Tapping lightly with a mallet is the best method of bending the prongs.

Snaprings

A snapring is a ring of metal, either round or flat in cross section, which is tempered to have springlike action. This springlike action will hold the snapring firmly seated in a groove. The external types are designed to fit in a groove around the outside of a shaft or cylinder, and may be safety wired. Safety wiring of an external type snapring is shown in Figure 5-77. The internal types fit in a groove inside a cylinder, and are never safetied. A special type of pliers is designed to install each type of snapring. Snaprings can be reused as long as they retain their shape and springlike action.

Figure 5-77. External type snapring with safety wire installation.

Figure 5-77. External type snapring with safety wire installation.