Washers

[Frank DolmanParticipant @frankdolman72357]

[Frank DolmanParticipant @frankdolman72357]

     When should one put a washer under (a) a nut (b) a bolt head?

[KWILParticipant @kwil]

Are you trying to spoil the paintwork/marr the metal surface both ends?

[chris stephensParticipant @chrisstephens63393]

Hi Frank,

The right size washer can go under both, but do  please keep it in proportion to the head.

 You can of course leave one out altogether, the historical precedent for this is given by the late Colin Chapman of Lotus fame. When watching one of his minions assemble a component with a washer under a nut, he was reputedly heard to say something to the effect of  “take that f—ing washer off, I am not paying for it to take a free ride around the race circuit”, but then we are not quite as concerned about our creations weighing a few extra grams .

chriStephens

[Martin WParticipant @martinw]

Hi Frank

 

Depends what you want the washer for.

 

Plain Washers, generally are used to protect the parts being bolted together and can allow a certain amount of movement between the parts. They also to some extent tend to spread the load and can take up small irregularities of the surfaces being joined, i.e. they can bend/deform when things are tightened. As KWIL says it gives a certain amount of protection to the paintwork/surface finish of the parts under the nut or bolt head.

 

Crinkle Washers are frequently used in areas where there might be some vibration and also they protect the parts being bolted together. They are a halfway house between plain and spring washers. They are normally thinner than plain washers but have a wavy profile that is compressed and the screw is tightened.

 

Spring Washers, these are used when there is likely to be a fair amount of vibration and are used to stop the nut/bolt unscrewing under these conditions. They actually dig into the surface of the material and the nut/screw and effectively form a sort of ratchet at the spring ends. As the name implies they are spring shape and often hardened to some degree.

 

Star Washers, these tend to be used where there are high levels of vibration and by their design are very aggressive in so much as they are frequently hardened and the many points dig into the parts being joined to form a multi-point ratchet. The surface of the material that has been screwed together under a star washer is normally pretty well chewed up or marked.

 

I know this is very basic but I hope it goes a little way to answering your question. I know that there are more qualified/experienced members of these forums that will be able to give you a better answer with a more detailed description as to where, when and why.

 

Cheers

 

 

Martin

Edited By Martin W on 08/12/2009 18:35:47

[mgjParticipant @mgj]

I think the Victorians used to be quite sparing on washers, in which case I’d use Loctite – but keep off certain paints.

 

On a lot of steam models you can bolt it up and paint over 

[Gordon WParticipant @gordonw]

Heres where I get shot down . On normal assy. washers are not needed, the bolt head and nut have a circuler face, the same dia. as a standard washer. Lotus, and aircraft etc do not use washers, extra weight, corrosion etc.. Spring washers do not dig in ,to any useful extent, did a test on them many years ago, nor do they “keep the nut tight”. A properly torqued bolt is stretched more than the spring in the washer, if you see what I mean. Star washers I always assumed, maybe wrongly, were for electrical contact as well as a little extra friction. The important washers are thick, to spread the clamping loads eg. cyl. heads, structural steelwork.

[Ian S CParticipant @iansc]

I quote my Pitman Aircraft Mechanic’s Pocket Manual(when I was in the industry I worked mainly on US aircraft)Washers-Plain(AN960)use of washers under nut or bolt.One washer shall always be specified on the drawing with each bolt or stud to prevent damage to the part or finish thereon.A steel washer shall be provided where the fitting is steel,and a heat treated aluminum alloy washer with aluminum alloy fitting.Aluminum and brass washers for electrical systems.The washer shall be assembled by the shop Under either the head of the bolt or nut,whichever is turned in tightening.Generally not more than one additional washer(total of two)may be used by the shop as pack washers,if neccessary,to adjust for cotter hole location or eliminate threads in bearing.AN is the American army navy standard which I beleave has been replaced by a new standard,nasa I think.Ian S C

[Gordon WParticipant @gordonw]

Very interesting Iansc, maybe that would be OK for mounting bits to the frame, esp. in US (dig, dig). 2 washers! When I started A/C D.O many years ago (D/Hav.) I was laughed at for suggesting using washers, thats how I remember.Washers not used for structeral joints. But as always open to correction.

[Tony MartyrParticipant @tonymartyr14488]

Washers are also used to minimise electrolytic corrosion when the clamped materials and bolts are well apart in the electrolytic series. We always had to use cadmium plated washes one the casing joints of royal Navy gearboxes. In fact aluminium will scuff badly under the steel nut if washers are not used.

[mgjParticipant @mgj]

Gordon – I agree. On the racer I always used 1/2 nuts to save weight! And we talk of 2 washers.! Quality made ali cast components have the litte steel inserts to stop scuffing.and one uses a dab of loctite to stop all unravelling. – and copaslip to prevent corrosion. Especially on Ti components – not that one would ever use Ti nuts and bolts a second time.

 

If I had to use a washer on ali, I’d use for choice one of those hardened very thin steel ones.

 

Nowadays though, in a lot of cases, holes are punched a bit oversize to allow for easy assembly and inaccuracies in production, so a washer one has to use. 

Edited By meyrick griffith-jones on 13/12/2009 01:00:18

[GoCreateParticipant @gocreate]

 

Hi everyone

I am a consultant in the bolting industry, it’s my job to design tools, calculate bolting requirements and provide procedures. Provided correct lubrication is applied washers are not used unless there is good reason to protect the surface of the component. On critical applications with high bolt loads thick hardened washers may be used to assist in load distribution and tightening method. Lubricants such as copperslip or coppaslip are termed anti-seize compounds, they lubricate for tightening then give corrosion prevention to assist in loosening. You have to be very careful which compounds you use depending upon bolt materials and operating condition.  Spring washers etc provide no benefit on structural applications, correctly designed and tightened joints don’t need any additional feature, or locknuts or anything, There are a couple of exceptions that employ tab washers or heavy duty Belleville washers. On critical joints use anti seize compounds, normal grease and oils increase the torque required and reduce control over bolt load. Don’t use molybdenum-based compounds unless you know what you are doing, you could put a critical joint into a dangerous condition.

 

Nigel

Edited By tractionengine42 on 13/12/2009 03:38:17

[Ian S CParticipant @iansc]

Just been rereading my Continental maintenance and overhaul manuals,all fittings attached by nut and bolt/stud- washer,lock washer,nut,except the conrod bolts-nothing,or the crankcase through bolts just a plain washer,but with a Palnut on top of the nut,a Palnut is a thin sheet metal nut that is tightened only 1/6 to 1/4 of a turn this is an effective lock.The washer and lock washer system is also used on the airframe of Piper,Cessna,and other US light aircraft.This may not be the case with heavy aircraft,but I don’t have any experience of any heavies other than DC-3/P&W R1830,they use the same system.the aircraft in the Pitman book are American WW2 piston engine.

[MikeParticipant @mike89748]

A few months ago, when I needed some info on nut and bolt technology, I found a very useful website. Sod’s Law being what it is, I forgot to bookmark it, and now can’t find it!However, I remember they recommended flanged nuts and bolts rather than washers as they generate superior  friction against the parts being held together, and are therefore far less likely to vibrate loose.

Also, no mention above of Nyloc nuts, in which I have great (maybe misplaced!) faith. Any thoughts from the experts?

Another also…Has anybody ever struggled to get a stuck sump plug out of a Mini? Popular rumour back in the 70s was that the thread form was such that it actually tightened under varying temperatures and vibration. Can this be true?

[CirclipParticipant @circlip]

Bellevilles are realy springs as opposed to “Gripping” spring washers and in cold applications Nylocs aren’t very grippy. Haven’t seen them approved for Aircraft applications. Remember seeing somewhere that to “Reactivate” Nylocs they should be immersed in boiling water to allow the thread deformation to un-deform.

 

   Regards  Ian.

Edited By Circlip on 13/12/2009 11:58:09

Edited By Circlip on 13/12/2009 11:59:49

[mgjParticipant @mgj]

Ian don’t aircraft applications always lockwire?

 

Quite willing to be proved wrong but on helicopters belonging to Crab Air and Teeny Weeny Airways, I don’t remember seeing any nuts and bolts that weren’t lockwired.

 

Nylocks are a once only use? I think.

[MikeParticipant @mike89748]

Hi Meyrick

I was always taught to treat Nylocks as one-use nuts, and I had certainly never heard of restoring them by boiling. I can also recall a thing I think was called an Evans nut. It had a horizontal cut in the top which caused the top of the thread to distort slightly. This slight distortion provided a very tight grip on the thread of the bolt or stud. All this goes back to the pre-Loctite days.

[CirclipParticipant @circlip]

Simmonds nuts and Aerotites and yes Meyrick, some of the nutted applications that didn’t have a self locking feature were torqued and wired. The normal aero types with the deformable section resulted in both the nut and bolt being bu**ered after one application, expensive but safer than having your bits drop orft.

 

   Yes, Nylocs have a one use application, straight into the bl**dy scrap bin BEFORE use.

 

  Regards  Ian.

[chris stephensParticipant @chrisstephens63393]

Hi Circlip,

Simmonds nuts were the original Nylock, but with red fibre instead of nylon. I remember reading about them in an old ME from the forties or early fifties, where they talked about this wonderful new invention!

No one has talked about the special flanged nuts with ratchet type serrations on the flange, to prevent unwanted loosening. These I suppose only work on soft surfaces.

Is there no end to man’s ingenuity?

chriStephens

[mgjParticipant @mgj]

You can get bolts with a dab of some coloured stuff on them already. Colour varies- I’ve seen blue and red, but maybe there are others.

 

This is a predabbed “dry” Loctite .

 

Convenient, if expensive. 

[Ian S CParticipant @iansc]

Nylok nuts are approved foraircraft use,and widely used,not suitable for temps above 120deg c,may be reused if they cannot be screwed on by hand.for temps above 120 deg c metal lock nuts are used there are 2 types,one has 6 little slots 1 1/2-2 threads down from top and distorted in ward,the other the top is squashed slightly oval.No not all are lock wired.Were I woprk these days nylock nuts are rejuvinated by giving the nylon end of the nut a whack with a hammer before refitting!Ian S C

[Gordon WParticipant @gordonw]

This is all very interesting, but probably not much use to Mr. Dolman who started this thread. When I worked in aircraft ind. many years ago there were different catagories of “risk” and this risk decided the locking methods to be used. On my old m/bikes Nothing stops nuts coming off exept a wack with a hammer, thank goodness for thread locking compounds. Do not tighten critical parts onto painted surfaces.

[Ian S CParticipant @iansc]

Talking of hammers,When the RNZAF came to rebuild the Bristol Freighters they found that no lock nuts had been used(and very few washers),plain nuts peined,the aircraft were not designed to be rebuilt.Ian S C

[Frank DolmanParticipant @frankdolman72357]

     I have to say that, contrary to Gordon W’s fears, the contributions to this

 thread have been for me instructive, interesting and amusing.  I was sorry

 to learn that spring washers don’t dig in much, they feel so nice as you do

 them up.  I shall go on using plain washers and lots of grease for general

 fixing for the same reason, though I now know that the washer contributes

 little and the grease may make things worse – but I might smirk a bit if

 the joint has to be undone again sometime.

     My thanks to all who have contributed so far.

[chris stephensParticipant @chrisstephens63393]

Rightho Guys, 

Now that we have got how-to stop nuts coming undone, shall we change the subject to how to assemble things so that they can come undone easily.

Personally I have no faith in Copaslip, especially on car exhausts, where the only answer is to change every thing to Stainless. For screws into crankcases, Aluminium motor cycle ones, I would strongly recommend wrapping PTFE tape around the screw/bolt before assembly. This does two jobs, it helps to stop water getting in and also provides a “slip joint” should corrosion start. A little grease under the head, of the screw not grease under the head on the pillow which is another matter all together.

In case any aircraft fitter says it upsets the torque setting, phooee, nobody uses a torque driver on the 6mm screws holding a gearbox sprocket cover on a Honda, but they curse when you can’t get the bu**ers undone because some numpty rounded the cross slot trying to undo a seized screw.

Anyone care to jump in with more horror stories to amuse and educate the assembled audience?

chriStephens

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