If the material under the lock washer is moving from high load, the lock washer will start to imbed and allow the fastener to loosen.
For high stress connections heat treated flat washers under the bolt head and self locking nut seem to be the best we’ve found.
Please read thread725-57042, thread725-63343, and thread725-85323.
PatCouture,
Helical split washers are worthless for most engineering applications. Please review the referenced threads (especially the one that links to NASA RP 1228).
Regards,
Cory
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
Thanks a lot Cory, I'm sorry for my lack of knowledge on the subject. But I've seen many people using them almost for any applications where there is a bolt in a threaded hole, and I never really knew if it was good use or bad use.
How about light components attached to a sheetmetal chassis by self tapping screws? It usually isn't possible to give these much torque and "shakeproof" washers (fan disc, internal and external star) are commonly used to lock the fasteners and also to help give electrical continuity,
You are describing a horrible joint. In the auto industry, they are not allowed - you have to use a proper nut (weld nut, staked nut, u-nut) so that you have a process-capable joint (high drive/strip ratio) as well as a joint that can withstand service loads. In your scenario the washers aren't necessarily redundant, the whole joint is not good. It is preferrable to design a proper joint and avoid "fastener magic" that usually doesn't work.
Regards,
Cory
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
I appreciate what you say and have argued for years against the use of spring washers in proper joints.
However it is a fact of life that many assemblies are designed and built to a price, often in the face of fierce competition. I am not talking about motor cars, but toasters, washing machines, computers, furniture.
Everything in life is a compromise; strength, weight, cost etc., and sometimes the market won't pay for anything better. I think there can be a valid case for specifying a shakeproof washer.
Spring washers certainly arn't the best device in the world, but they do have there uses. I've found in low load, high vibration enviroments such as on industrial reducers they are highly effective at locking up small dia thereads (not as good on large dia bolts as they work out too easily)
