Lock washers unnecessary??

TxDoc · Sep 12, 2016

I did have a stroke in Feb, but you may think I've lost my mind, still. I could swear that I read on this forum, in a technical article with data to nvm out up....That lock washers not only didn't increase retention, but actually decreased it.

Dies anyone recall. that and if so, do you have a link to it.

If I udder list my mind..go ahead, I can take it.
Thanks
Dr Mark

Monarchist · Sep 12, 2016

TxDoc said:
I did hinge a stroke in Feb, but you may think I've lost my mind, still. I could swear that I read on this forum, in a technical article with data to nvm out up....That lock washers not only didn't increase retention, but actually decreased it.

Dies anyone recall. that and if so, do you have a link to it.

If I udder list my mind..go ahead, I can take it.
Thanks
Dr Mark

I think ... that the post - or the external citations - had to do not with lockwashers, but with jam-nuts, and how tightening them in the 'obvious', but WRONG sequence actually degraded the force.

No stroke here.. YET... but I've paid enough dues to have earned the right, so... "in due course".

Bill

SAG 180 · Sep 13, 2016

From Loctite's "Technology of Threaded Fasteners" page 40 is a nice chart of how long various locking methods last under vibration. You'll notice the spring type lockwasher lasted less time than the control.

180344d1473743035-lock-washers-unnecessary-loctite-page-40.jpg

DanielG · Sep 13, 2016

That's a good chart SAG 180.

As the chart shows, lock washers don't do much. Here's what NASA has to say on the subject:

"Free spinning split lock and tooth lock washers provide minimal, if any, locking."

That NASA standard (NASA-STD-5020) is one of my go to resources for bolted joint design. The other big one is the AISC spec when you're dealing with a shear joint.

ManicMetalBasher · Sep 13, 2016

Ymmv

Long ago I bought a used Vauxhall [= GM] car.
A week later, rattling under the bonnet. [UK terminology]
Cause, loose engine mountings, solution, tighten washer faced screws on mountings. [Not on the #3 graph]
Seven days thereafter, rattling under the bonnet, cause as before, "solution" as before.
Several problem/solution events later, replaced screws with genuine OEM parts. [I assume the discarded parts were also OEM]
Several more problem/solution events later, replaced OEM parts with standard screws and spring washers.
No more problems in the six following years I owned the vehicle.
[Conclusion - I know more than GM]

Only one example.
YMMMV, well mine varied, considerably.
Why no oval, deformed thread nuts, on the "expert" graph?
Why no serrated "Binx" nuts on the "expert" graph?

cyanidekid · Sep 13, 2016

see the late Carroll Smith's " Nuts, Bolts, Fasteners, & Plumbing handbook" not everything is up to date in this 1990 classic (seems wrong to say that to me, guess i'm old!) but, it is required reading for sure.

SAG 180 · Sep 13, 2016

ManicMetalBasher said:
Why no oval, deformed thread nuts, on the "expert" graph?
Why no serrated "Binx" nuts on the "expert" graph?

The document does mention deformed bolts and nuts in the earlier pages, My only experience with deformed bolts and nuts was in a 1973 Ford Falcon coupé where they were used all over the chassis and for bumpers: they all sheared off or stripped when trying to undo, so they seem to be a one use fastener. As far as Binx nuts, that document was published in 1974 in the USA, Binx from what I can see is a British 1960's vintage nut, so maybe they weren't all that common in the USA when the article was written.

BillE · Sep 13, 2016

Video of a Helical Spring Washer subjected to a Junker vibration loosening test

cranium · Sep 13, 2016

Curious if the bolts/washers in question have been torqued to the mfg's specification?

SAG 180 · Sep 13, 2016

BillE said:
Video of a Helical Spring Washer subjected to a Junker vibration loosening test

That's the kind of test the Loctite chart refers to: transverse vibration.

HuFlungDung · Sep 13, 2016

I don't suppose all spring lock washers are the same. I don't like them, the good ones score the shit out of surfaces when undone. But they need to be hard and sharp edged to do that. And the thing about the sharp edge, is that it is impossible for it to grab anything when squashed flat, because it has no relief. So the nut would have to partially unscrew before the lock could attempt to dig into the nut/surface, because it doesn't dig in at all when the thing is torqued up, wrong direction.

dgfoster · Sep 13, 2016

BillE, Thanks for pointing out the Junkers test machine. Very interesting. Here is another video that has a bit more explanation of the machine and the mechanism of bolt loosening:

And, SAG180, how did you access Loctite's "Technology of Threaded Fasteners" ? I searched some but I could not find it online. Sounds like an interesting resource.

And thanks to the OP for getting this thread started.

Denis

SAG 180 · Sep 13, 2016

dgfoster said:
And, SAG180, how did you access Loctite's "Technology of Threaded Fasteners" ? I searched some but I could not find it online. Sounds like an interesting resource.
Denis

My Fitting and Turning Guru has a paper copy with a publish date of 1974. I've tried to get a new copy out of Loctite Australia, but unfortunately it's been replaced with watered down documents. I'm attaching a couple of pages under "Fair Use" in case someone has an old copy somewhere they can recognise.

JNieman · Sep 13, 2016

If it's a heavy or higher torque application, pre-loading the fastener is the best retention. If it's a low torque light load, chemical locking means is preferred, though nylon/plastic insert bolts work well, too.

Point is, for heavy duty situations, washers ain't doing jack shit to resist rotation. Proper torque does. Making the bolt longer, to improve tension, is also a successful solution. Turning a cylindrical spacer to take up the gap between the the first ply and the bolt head (typically with flat washer) is dandy. I've read about using heavy duty compression coil springs between the flat washer and first ply, but that's outside my experience. If you're using heavy duty die springs and torquing against those, I guess that'd work - seems logical in my mind, anyways. Just never done it.

So the best locking method depends on the application. Do you need to ensure installed bolt tension is maintained? Do you just need to not lose the nut? Is it a slip critical connection or just keeping something from moving around? Those will be factors that decide on what's 'good enough'.

Lock washers shouldn't be the answer to any of those equations.

JNieman · Sep 13, 2016

For 'free' resources in the public domain, there's a NASA doc on fastener and bolted connection design which goes over industry standards (of the time) but is obviously a bit aerospace focused. "NASA-RP-1228"

My go-to is a fastener design reference manual from Unbrako when I'm not using the AISC Steel Construction Manual.

gwilson · Sep 13, 2016

Some lock washers only work ONCE. That may have been the problem with the Vauxhall.They lose their keen holding edges when being loosened from their first application.

JNieman · Sep 13, 2016

gwilson said:
Some lock washers only work ONCE. That may have been the problem with the Vauxhall.They lose their keen holding edges when being loosened from their first application.

If the nut has backed off enough to cause deformation on the mating surface which will allow the edge of the lock washer to dig in, that means the nut has rotated - you've just lost your torque and thus your required tension in the bolt.

WizardOfBoz · Sep 13, 2016

It seems to me that the lesson here is that for transverse (is this not just shear loading?) it's important to have very close fits on bolt diameter, possibly using shoulder bolts, or adding locating pins. And for shackles and clevis-type arrangements, to use double-shear mount (that last point is emphasized in the Carroll Smith book cited above).

And to torque to spec, to maintain proper bolt stretch and axial clamping force.

The loc-tite graph is pretty convincing.

strokersix · Sep 13, 2016

Bolt Science Web Site

Good info at this link. Especially joint diagrams. If you understand these you will be better prepared to design bolted joints solve fastener issues.

crossthread · Sep 13, 2016

I recently had a situation on my boat where I was trying to bolt an auxiliary outboard to the transom. I was using SS all thread since I needed bolts that were about a foot long but only 3/8" in diameter. I used SS lock washers and found that from the vibration of the motor, pounding on the water etc. the nuts were quite loose and some had almost vibrated off. I did not want to use chemical locking due to the harsh environment (may have been fine but I didn't want to take the chance on losing a $3K motor). I contacted Fastenal here and they told me to use something called T-lock nuts. These are nuts with laser cut slots. The people at Fastenal said they would hold better then Nylocks. They are very pricey but seem to work well. I will say that after two seasons the nuts are still tight.

Lock washers unnecessary??

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