Staying tight

Date:1 June 2010 Tags:

Safety wiring was developed for the aircraft industry to prevent critical fasteners from loosening in mid-flight, a development that could ruin a perfectly good holiday. Thin stainless-steel wire is used to tie bolt heads and other fasteners to each other to prevent them from unscrewing themselves. I use this technique all the time on racing cars and motorcycles, because the vibration can eventually overpower even a properly torqued bolt.

The process also ensures that everything has been assembled to its final torque spec, because you can simply go over the vehicle with a checklist and visually verify the presence of the safety wire without having to get out a socket or spanner and trying to tighten every fastener. The hardest part of installing safety wire is cross-drilling the bolt heads. That tiny 1,5 mm drill bit snaps easily, usually just as the bit is exiting the far side of the bolt. This will not only ruin the drill bit, but potentially an expensive, high-quality bolt, too – that’s if you can’t get the bit loose.

I use a really neat drilling fi xture from Graham Tool (www.grahamtool.com) and a cheap drill press, which makes the procedure easy. Clamp the bolt head to the fixture and clamp the fi xture to the drill press table. A careful guy could do it with a bench vice and a hand drill, but skip the coffee that morning to keep your hand steady.

Install the bolt and torque it properly. If the hole doesn’t line up correctly, you may have to drill a second hole, or try a different bolt. I generally use 0,8 mm aircraft stainless lock wire, which you can get at some speed shops or aircraft spares suppliers. (Iron “mechanic’s wire” won’t do.) A handy item if you’re doing a lot of safety wiring is special safetywire pliers used to cut, clamp and twist the wire. Lone fasteners that don’t have a nearby partner may require that you drill a hole in a nearby bracket, or add some other type of stationary point to thread the wire through.

How to install safety wire

1. Start safety wiring by cross-drilling, or buy crossdrilled hardware. This fixture uses a collet to hold the bolt head steady and guide the drill.

2. There are special safetywire pliers for installing the stuff, but you can do it with some small locking pliers. Wrap and twist the wire from one bolt to the next so the bolt heads can’t come undone without removing the wire.

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