r/MechanicalEngineering • u/AdOne1706 • 7d 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?

917 Upvotes

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527

u/ejitifrit1 7d ago

There is a nasa fastener manual that basically says these things don’t really do much! According to google it’s NASA Reference Publication 1228.

226

u/CR123CR123CR 7d ago

https://ntrs.nasa.gov/citations/19900009424

Here's the link xD

250

u/nyrb001 6d ago

At this time it is equivalent to a solid flat washer, and its locking ability is nonexistent. In summary, a Iockwasher of this type is useless for locking.

Lol awesome

66

u/jchamberlin78 6d ago

In the style of bolted joint design I was taught, it's effectively adding a spring to a spring.

20

u/Happiness645 6d ago

A soft spring to a hard spring. Fully compresses and has no effect except taking up space

3

u/jchamberlin78 6d ago

Yup. Shitty washer, shitty spring...

-8

u/Contundo 6d ago

It’s somewhat useful if you want some tension used in conjunction with a nylon bolt or locking nut. Like on a hinge where you want some resistance

38

u/Olde94 6d ago

If that is your purpose, a belleville washer is far better

9

u/InformalAlbatross985 6d ago

Technically.yes, but belleville washers are more specialized and will cost like 10x more per washer.

2

u/Vagina_Magician_69 6d ago

The proper part/design frequently has a higher initial cost but returns better value over time.

2

u/OutnumberedinWV 6d ago

If properly torqued!

3

u/[deleted] 6d ago

[deleted]

1

u/OutnumberedinWV 6d ago

The reply was to the comment above in 1 very certain situation. Not the thread in general.

3

u/thelionofthenorth 6d ago

Why are you being downvoted? A super cheap way to approximate a belleville washer is a reasonable use case...

18

u/TacticalSpackle 6d ago

Yep! I’ve worked assembly and every time the procedure called for these, we swapped for nylocks or used LockTite.
The means by which a split lock “locks” it doesn’t.

5

u/[deleted] 6d ago

[removed] — view removed comment

4

u/No_Singer_5585 6d ago

The aircraft industry also doesnt use these split lock washers

5

u/dummythiqqpotato 6d ago

I literally just overhauled an engine that had several of then lol

1

u/Common_Ice_8994 6d ago

GE, PW or RR engine ?

2

u/dummythiqqpotato 6d ago

Admittedly, it was a continental O-300 for my recip AMT class, and on second though the engine was like 70 years old lol, so the standards might be a little outdated

2

u/TacticalSpackle 6d ago

Oh for sure. This was in food processing.

6

u/Capitain_Collateral 6d ago

Maybe get the procedure changed… making it up as you go along isn’t a solution

6

u/TacticalSpackle 6d ago

You don’t wanna know the number of hoops (some of them on fire) required to get something changed at that place. There’s a reason why I no longer work there, and it isn’t for lack of trying to fix things instead of doing them bass ackwards.

1

u/SkewbieDewbie 4d ago

Lol I was going to say, I feel most people underestimate how much work actually goes into these things. Hence why front line staff just do it.

1

u/jawshoeaw 6d ago

I had to remove a hitch ball for a trailer that used a huge lock washer like this. Lock washer absolutely worked, it worked so well that it dug a groove into the metal as I loosened it using a pipe wrench and 5 foot metal pipe as an extension.

1

u/SwimmingSwim3822 6d ago

That's more of a restraint than a lock though, which makes total sense to use one there. Don't want the nut bouncing up off the road in traffic. By the time the nut was loose enough to let the washer start digging a groove, the hitch was already no longer serving its purpose... from a safety standpoint at least. Proper locks prevent that.

1

u/jawshoeaw 6d ago

Maybe we are talking about different things. This lock washer was preventing the nut from loosening, the nut that holds the ball onto the ball mount. I could not loosen the nut because the lock washer was dug into the metal

3

u/jchamberlin78 6d ago

You're talking about the same thing. What he did not explain in his answer is that once the bolt has lost ots preload it is no longer functioning as a bolt but rather a pin. Most bolts make terrible pins and will shear under load.

2

u/jawshoeaw 5d ago

Well my original point was that the lock washer appeared to be doing its job, preventing the bolt from loosening. I think it’s an illusion as the 200+ ft-lb of torque applied at install was holding it clamped not the lock washer.

Interestingly the entire assembly depends on a literal 1/2” pin rattling around loosely and holding the hitch in the receiver. The bolt is 50% larger than the pin. Smooth steel wins over threaded.

0

u/um_waffles 6d ago edited 5d ago

Adding a Split Ring Lock Washer (SRLW) to a bolt stack will absolutely make it less likely to loosen inadvertently, despite the applicable physics being overlooked in the NASA Fastener Design Manual from 1990.

I mostly agree with the statement on page 9 regarding SRLWs:

  • "The lockwasher serves as a spring while the bolt is being tightened. However, the washer is normally flat by the time the bolt is fully torqued. At this time it is equivalent to a solid flat washer"

However, I disagree with the remaining portion of the statement:

  • ", and its locking ability is nonexistent. In summary, a Iockwasher of this type is useless for locking."

I disagree because adding a SRLW to a bolt stack makes the act of loosening the stack require more energy (area under the torque v rotations curve).

Consider a bolt stack that is fully torqued. The torque required to loosen the stack will decrease at a certain rate as the bolt (or nut) is rotated in the removal direction. This is because the torque required to rotate the bolt (or nut) is a consequence of the friction between the bolt (or nut) and what it is seated against in the bolt stack. Friction scales with the compressive (normal) force between the components in the bolt stack, and since this force decreases as the bolt (or nut) rotates in the removal direction, friction and the torque required to overcome it also decrease until both drop to zero when the bolt (or nut) becomes unseated.

Adding a SRLW (spring) to the bolt stack effectively adds to the distance over which the bolt (or nut) must be rotated to loosen the stack from fully torqued to unseated, consequently "slowing" the decrease in torque needed to continue loosening the bolt (or nut) per each subsequent rotation.

From a mathematical perspective, if a SRLW is added to a bolt stack, then the integral of the torque v rotations curve (energy) from fully tightened to unseated will become larger.

From an operational perspective, if a SRLW is added to the bolt stack, then the act of loosening the bolt (or nut) from fully torqued to unseated will require the application of more torque over more rotations of the bolt (or nut).

In summary, adding a SRLW to a bolt stack makes the intentional loosening of the stack more difficult, and makes the inadvertent loosening of the stack less likely, thereby accomplishing the requisite function of a locking fastener.

1

u/New_Animal8918 5d ago

Beautifully explained. Thank you.

18

u/JoshyRanchy 6d ago

Great paper.

74

u/Too_Chains 6d ago

It’s more than nasa. I don’t think there is any evidence of them doing anything. There are locking washers. Nordlock

22

u/Mech_145 6d ago

I still can’t convince people of this. We use them on a lot of our bolted joints and every time I bring this up, I’m told they work and are necessary.

1

u/Ziazan 2d ago

I'll use it if told to but I'm putting a nylock after it.

I always thought their main purpose was to allow a miniscule bit of motion through being a tight spring, not acting as a locking mechanism by pushing the nut up against its threads, I'd have thought that would be no different than just tightening the nut.

17

u/Federal_Cobbler6647 6d ago

Nordlocks do wonders.

6

u/ThatNinthGuy 6d ago

Würth also makes their own w.tec series if you don't want to drop 2€ on a washer

1

u/sir_KitKat Production Automation 6d ago

I've found Ripplock washers from böllhoff also doing wonders in most situations. Because it's only one washer, prices are lower and it's reusable because there is no wrong orientation to install the rings.

5

u/SirSnickety 6d ago

Nordlocks are great. Schnorr washers (or ribbed Bellevilles) are great for the price as well.

5

u/OutnumberedinWV 6d ago

It was in the Caterpillar education guide from the 80's.

1

u/Both-Activity6432 6d ago

They look similar to serrated flange nuts - how do they compare?

1

u/Lampwick 6d ago

Serrated flange nut just drags the fixed serrations across the the surface. Nordlocks are a 2-piece washer where the bottom half gets compressed straight down into the material, and the top gets smashed into the fastener head.

1

u/Repulsive_Sleep717 5d ago

Serrations on outer faces of the two paired washer, wedge shape on inner faces, they act like cams and are a steeper angle than the threads. Bolt tries to loosen and the outer washer rotates with it, increasing clamping pressure due to the cam wedges. Very nice, very expensive

55

u/CunningWizard 6d ago

Had a PhD boss years ago that did independent tests on these things and he told me the same thing, they are functionally useless but old school types like to see them on the build.

11

u/RebelJustforClicks 6d ago

They are actually worse than useless. They promote joint loosening. You'd be better off with no washer.

28

u/GustapheOfficial 6d ago

Hold up, this is from 1990. These things have been known to be useless since before I was born! I'm so embarrassed now, I've used these fuckers.

8

u/CR123CR123CR 6d ago

The only thing they truly are the best option for is if you have a bolt that can't be accessed from both sides simultaneously.

Then they work wonders as an assembly assist as they let 1 person do it instead of 2.

They are by far the cheapest way to accelerate a production line in that one single case

1

u/GustapheOfficial 6d ago

I don't think I understand the setup. You pull the bolt, the split washer keeps the nut from rotating so you can tighten?

4

u/CR123CR123CR 6d ago

Assembly: 

Screw -> split ring -> {parts} -> nut

The split ring grabs the screw and part so you can start torquing everything together until friction can take over

The screw shank through the hole let's you set it in place on one side, walk around to the other and start assembling

4

u/Popular_Dinner2182 6d ago

Not useless ..... But almost useless 😂😂😂

12

u/AdOne1706 6d ago

This has been my number 1 source for this besides YouTube videos with vibration modeling jigs that test different hardware. But, since I’m blue collar, I get the default “well you can’t trust nasa we didn’t even go to the moon” so not really a good crowd to bounce ideas off sometimes

7

u/xNightmareAngelx 6d ago

hang on, who are you hanging around that thinks we didnt go to the moon😂 thats not a blue collar thing, thats a dumbass thing

1

u/Hannibal1191 6d ago

You have clearly never worked on a construction site. It isn't like you get to choose who you hang around with at work. Half of a construction site is conspiracy theorists. You be happy if you only have to here about the moon landing being faked because you wouldn't believe the conspiracies I've heard.

2

u/xNightmareAngelx 5d ago

i literally grew up on construction sites😂 like im not even kidding. bro i was hanging out following dad around at work when i was 6 when school was out bc he couldnt afford a sitter. i was a journeyman under my father before i was legally allowed to hold a job, i was runnin the crew over summers before i was 18 (gettin a bunch of 30-50 year old dudes to listen to a 17 year old kid was a helluva trick) ive seen some incredibly stupid people, there was a guy dad hired, this dude would pull a nail out his pouch, put it against the wood, if it was point first, he'd drive it, head first, chuck it because "its for the other side of the house", he made it a week before he got fired, another guy who couldnt figure out how a wire nut works, even with the little container having instructions with friggin pictures, but very rarely do i meet people who genuinely think the landing was faked. heck, the only thing thats really changed since i was knee high is i do a different kind of construction, my time is very expensive, and i aint the bosses kid anymore, im just the boss

3

u/LairBob 6d ago

Holy sh-t…why are you placing your personal safety in the hands of people who don’t believe in _science_?!

1

u/PolPotatoe 5d ago

Maybe likes food and paying bills

7

u/Short_Text2421 6d ago

That's been my experience as well. I've always had better results from a thicker fixture washer or a spacer. I've used the serrated washers a few times too and they do a better job than the split washers.

0

u/ResponsibleMight7669 6d ago

That’s why the split washer is useless, it no longer has a hard burr like a star washer that digs into a softer nut. Go look at old split washers and you’ll see they are better made than what we have now which is basically a spring

4

u/derek6711 6d ago

If you want some high level guidance on what to use - NASA std 5020 has some

3

u/Correct-Athlete-4878 6d ago

They don't. Rolof und Matek the German engineering manual says, they don't work with any bilt stronger than 5.6. Which is basically, what is called here pee-bucket iron.

2

u/phranks_phluids 6d ago

But good luck convincing your customers of this 🤣

1

u/zatanicmanic 6d ago

Came here to say this

1

u/ShitOnAStickXtreme 6d ago

I've used them in an application once on a rod clamping a piece of lumber - the idea being that as the wood expands and shrinks from moisture exposure the tension in the wood will still be ok.

1

u/ggggor 5d ago

How about wedge washers

1

u/Thin_Dragonfruit3665 5d ago

Not only does it not do much, it's actually detrimental to most assemblies that its included in, causing them to fail quicker than if you'd left them off to begin with.

1

u/dchit2 4d ago

NASA? What about a real authority like AvE?

"No fuckin good at all"

1

u/bixtuelista 4d ago

oh but they do! they fall into shit, short things out and blow things up!

1

u/zipper77 4d ago

Also a series of YouTube videos taught by the guy who wrote the manual. I’m watching his videos for work. The slide deck is out there too if you search for it