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Topic Title: Locking methods for bolts and nuts
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Created On: 28 November 2010 06:49 PM
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 28 November 2010 06:49 PM
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ebanner

Posts: 48
Joined: 18 January 2003

I've been reading up on this subject and found some interesting things:

If you are intending on torquing the bolt/nut assembly then a spring or crinkle washer is redundant. This is because when you torque the bolt/nut assembly it is in tension and the force is far greater than any force exerted by the spring or crinkle washer. In effect the spring/crinkle washer act as just a plain washer. This is apparently the view of NASA and the UK Defence Industry. From what I have read it seems that a star washer or Locknut or Loctite glue should be used as it stops the nut turning.

This does not explain then why spring/crinkle washers are on sale? I presume that these washers should only be used on bolt/nut assemblies that are just tightened enough to compress the washer?

Are there any good tutorials that anybody knows about?
 01 December 2010 10:24 PM
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jencam

Posts: 608
Joined: 06 May 2007

A useful bit of info from my son...

The purpose of a crinkle washer is to allow a small amount of movement of the bolt / nut assembly in order to prevent stresses caused by expansion and contraction with temperature, or more usually, to damp vibration conveyed through the bolt. The bolt / nut assembly should be tightened to a torque where the washer just begins to compress. If it is overtightened then the washer is squashed flat and loses its effectiveness. Most crinkle washer manufacturers provide optimum torque figures for their washers but is is possible to feel when the washer begins to compress if no torque figure is available.

My son fitted crinkle washers to his BMX to reduce vibration at certain frequencies.
 03 December 2010 10:18 AM
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ebanner

Posts: 48
Joined: 18 January 2003

Thanks for the reply! I have been doing a bit more research. I think there is a lot misinformation about this subject!

My thoughts are after consulting some workmanship manuals:

If you torque a bolt/nut assembly then a locking washer is not needed because the bolt is now under tension and this force is much bigger than the force that a locking washer could apply. This force is acting on the threads causing friction.

If you don't torque a bolt/nut (e.g. a screw holding a PCB) then a means of locking is required. This can be by a locking washer or loctite glue. When you tighten the lock washer should be completely compressed. This compression applies back pressure and friction on the threads as before but just not as much.

A locking washing can be crinkle or spring but you always need to put a plain washer for spring to avoid it damaging the surfaces. You don't need this for crinkle. A plain washer is just there to protect surface or distribute/stabilise load of bolt/nut assembly. You always need a plain if bolting down to soft material like plastic.

Next question when is a bolt a bolt and a screw a screw!
 03 December 2010 12:28 PM
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amillar

Posts: 1918
Joined: 28 May 2002

Just to confuse things: a spring or shakeproof washer will have a recommended torque. For maximum retention you would both fit a spring washer and tighten it to the correct torque. Apparentely this will leave it slightly sprung so that the 'tang' of the spring is biting into the nut.

(I have to thank one of my colleagues who knows far more about this than I for this information!)

-------------------------
Andy Millar CEng MIET CMgr MCMI

http://www.linkedin.com/in/millarandy

"The aim of argument, or of discussion, should not be victory, but progress." Joseph Joubert
 04 December 2010 10:02 AM
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ArthurHall

Posts: 735
Joined: 25 July 2008

Next question when is a bolt a bolt and a screw a screw!

My understanding is that a screw is threaded all the way while a bolt has a plain section.
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