For your (engineer's) eyes only.

[Digit]

I am still rebuilding my latest two wheeled purchase, which is a bit of a misnomer as I'm still removing parts!
Never the less, can some one explain to me the reasoning behind using both a plain washer and a spring washer under a nut?

Roy.

 

[CHJ]

Plain washer provides a more even spread of clamping load, bridges any oversize bolt clearance hole and protects the underlying surface.
The spring washer can be considered as just an extension of the nut and sole purpose is to resist the nut reversing under vibration.
Any damage done by the spring washer digging in is restricted to the plain washer and not the underlying finish.

 

[myturn]

Spring washers are no longer considered as helping prevent a bolt under torque from loosening, on the contrary they can actually make it more likely to come loose.

Locking nuts or thread locking compounds are advised instead.

Here's a very informative website with all you need to know about nuts and bolts.....to get to the main contents page go to the bottom and select "Bolting Info"

http://www.boltscience.com/pages/helicalspringwashers.htm

 

[andycktm]

I think the point hes trying to make is the spring washer is bitting into a plain washer which is not anchored to anything

 

[Digit]

I think the point hes trying to make is the spring washer is bitting into a plain washer which is not anchored to anything

Exactly! and thus the spring washer performs no useful function what so ever!
I was unaware of the Junker test but agree that it supports my own experience. Now a days I use Nyloc nuts and plain washers or Loc-tite.

Roy.

 

[barkwindjammer]

If you screw a nut down and call that travel 'in-bound', when the nut is torqued-its thread is pushed against the thread of the bolt (lets say) in an 'out-bound' direction, the split/sprung washer helps to hold/add to this tension, its true that the ny-loc nut and locking compounds have superceded this. I see where your coming from Digit, you would assume that the little ridges formed on both sides of the washer would bite into the opposing faces-but thats not how they work.

 

[Digit]

Well how do they work?

Roy.

 

[barkwindjammer]

They work very well as it happens, just not well on a rig like is shown in that video posted (which is putting a very specific force on to the fastener), they simply apply 'out-bound' tension to the threads-counter intuitive I know-but thats how they work, for a motorcycle-plenty of locking power, like I mentioned ny-locs are better and stainless :wink:

 

[myturn]

If you screw a nut down and call that travel 'in-bound', when the nut is torqued-its thread is pushed against the thread of the bolt (lets say) in an 'out-bound' direction, the split/sprung washer helps to hold/add to this tension

The helical spring washer interferes with the friction between the bolt head and the mating surface (flat washer or the material that is being held). This friction contributes greatly to the security of the fastening and is a consideration when calculating the torque. This is why you should never lubricate under the head of a bolt that is done up in a torqued application.

 

[CHJ]

I think the point hes trying to make is the spring washer is bitting into a plain washer which is not anchored to anything

The plain washer is anchored by the friction between it and the underlying surface, washers are usually fitted at design phase for reasons other than obtaining maximum grip and should be selected on thickness and diameter to provide adequate 'natural' resistance to movement against the underlying surface.
Nylock nuts should be used with caution where heat such as engine or gearbox is involved as they can flow, Aerotight mechanical lock nuts should be used instead.

 

[Digit]

I was an engineer for over 50 yrs, including aero space, nuclear and oil rigs, thus I am familiar with various locking systems, and their weaknesses.
The reason I asked the question is a debate elsewhere.
One objection to spring washers is the damage they can do when removing the fastening, particularly against a soft sub strate, this I suspect is one reason manufacturers will use a plain washer as backing.
As a locking method, when backed by a washer they are, in my experience, ineffective, a tab washer is vastly superior.

Roy.

 

[CHJ]

I think it's a case of horses for courses Roy. Obviously as you say where a loosening nut would lead to a catastrophic failure then wire locking, split pin, tabbed washer etc. are the norm, spring washers may be at the bottom end of the rotational security and may be one step lower than a K-lock etc. but there is no doubt that for thousands of low end applications they are effective enough and prevent that initial release of tension cost effectively.

 

[myturn]

According to most studies when a joint using a helical spring washer is fully tightened the washer is normally flat and as such is no more effective at locking than a flat washer.

Where they are used in applications where there is no movement or vibration there is no need for locking (hence they are redundant), and where there is movement and vibration they are ineffective at locking and as the tests show can actually make the joint more likely to come undone.

They will not prevent any initial release of tension whatever the application.

So it would seem that where they are still used it is misguided and because "we always used to do it that way".

 

[Digit]

Logic forces me to agree with Chas, it's the placement of the additional plain washer that causes my to question.

Roy.

 

[chris_d]

One more thing to consider before you dismiss spring/split washers and their use in tandem with a plain washer:

Where the substrate being fastened may shrink (eg timber) then the spring washer gives some margin for shrinkage before the fastening becomes completely ineffective.

I recently used plain (square) washer and a spring/split washer to bolt together three rafters to make a larger laminated rafter at the cheeks of a roof dormer.

 

[Digit]

I go a step further. I use the large diameter special toothed (dunno what you call 'em) washers then the spring washers.
Horses for courses.

Roy.

 

[jasonB]

Chris in this instance a belleview washer or several would have been better but I've never seen structural timbers fitted with any form of lock nut, lock washer or spring washer before.

Jason

 

[chris_d]

I go a step further. I use the large diameter special toothed (dunno what you call 'em) washers then the spring washers.

I used the 'double sided timber connectors' you refer to between the two timbers that I was bolting together.

 

[chris_d]

Chris in this instance a belleview washer or several would have been better...

Thanks for the reference, I've just read up on them and they seem pretty useful for all sorts of situations!

...but I've never seen structural timbers fitted with any form of lock nut, lock washer or spring washer before.

I'm special...not really - I just had some M12 spring washers to hand!