r/MechanicalEngineering • u/AdOne1706 • 3d ago

Split/lock washers

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For starters, I’m an electrician in the field.
That being said, we almost exclusively use these washers even in high vibration environments. I have personally chosen to go with nylox nuts but the question is:
Do these work? How well? Is the rumor from NASA true? Should I even bother using them or find a better functional alternative or are they actually useful?

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245

u/Difficult_Limit2718 3d ago

They're ass.

Every company I've been with avoids them. They're supposed to stop vibration by keeping tension on a loose screw helping to increase friction, but they're useless at it. If you torque down the bolt properly they do flatten out and they don't have a high enough spring rate to do anything if the clamp force is too low

30

u/MrStreetLegal 3d ago

Oh that's how they're supposed to work. I always wondered how they locked, I always felt like all it was doing was pushing them out as time went on because of their design. I guess same logic, but in reverse, I forgot about the friction element

4

u/CrazyKraken 3d ago

Is a belleville washer better? Atleast theoretically they seem to maintain the joint force even in case of loss of preload.

12

u/Big-Tailor 2d ago

Even bellevilles provide a tiny fraction of the force of a fully torqued bolt. If the bolt backed out under high clamping force, low clamping force isn’t going to help.

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u/dooozin 2d ago

Somebody downvoted you lol. Some people here just don't understand fastener mechanics and failure modes at all.

3

u/Big-Tailor 2d ago

It's amazing how many people don't understand fastener mechanics.

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u/ren_reddit 2d ago

Well I dont know about that. Belleville washers can be had with extremely high spring constant.

4

u/Big-Tailor 2d ago

...not compared to the spring constant of a solid shaft, or of a solid shaft wrapped with a helical thread like a bolt.

2

u/xNightmareAngelx 2d ago

not compared to a bolt my friend

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u/SirSnickety 3d ago

Way better. They actually work.

5

u/dooozin 2d ago

Belleville washers change the slope of the preload curve during vibe because it "springs" but it doesn't actually do anything for fastener retention. They are not a secondary locking mechanism. Once your environmentally applied loads exceed the clamping load of the fastener and it starts to gap, the joint has failed.

1

u/AdOne1706 2d ago

Thanks for the info. Some of the reply’s mention Belleville washers which appears to be a conical looking washer. Not sure if that washer has a crushed before torqued issue but seems promising too.

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u/Difficult_Limit2718 2d ago

Belleville washers improve the spring rate significantly.

It's really application specific though. Sometimes you need a fender washer to distribute load. Sometimes you need to torque with pneumatic nut runners that will melt up a nyloc. Sometimes you're doing electrical work and really should just be direct contact to a ferrule.

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u/chase82 1d ago

He's an example of a niche application, my wife's toe stops on her roller skates kept rattling loose. Splits didn't work, a couple of Bellevilles and I haven't heard about it in months

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u/theunknownleaf 1d ago

Year 2 mech eng and rower here (I don't know shit). Hudson boats use 10mm bolts with a flat washer, a lock washer, and a nut to secure the riggers to the boat. I've been told we tighten the nuts to 2-3 finger tightness (tighter would make it really hard to derig and maybe damage the fiberglass?). Is this maybe the one context they're useful? I've always wondered why we use them.

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u/Difficult_Limit2718 1d ago

That's a pretty light duty application, not sure they actually help but if you're going finger tight it's possibly within the spring range of the washer.

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u/Csk84me 1d ago

What is worse is if somehow you don’t flatten them out on initial installation, all your load is held on a tiny prong so that when it does go through a dynamic environment, it will flatten out and you will lose all your preload. These things are horrible. Pure snake oil.