Useless Lockwashers - So Says NASA

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GregGleason

GregGleason

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From NASA publication RP-1228, 1990, pp. 9-10:

NASA.on.Lockwashers.NRP-1228.jpg

I always thought these things were the way to go for washers. Apparently not.

Greg
 
They always worked where I've seen them in use. If you flatten them out like they are supposed to be they are putting tension on the assembly.
 
I suspect some physical friction is being ignored in this conclusion. The sharp edge of the diagonal cut on the washer digs into the surface slightly, and improves it's performance. A shake test would prove that.
 
They don't work as well as the multi-toothed ones but help some. The cut is angled so the ends dig into the bolt and mating surface if the bolt is loosened.
 
Now I don't feel so bad about having so many left over when I put something back together.
 
ThirstyBarbarian said:
Now I don't feel so bad about having so many left over when I put something back together.
Click to expand...
I always figure that if the manufacturer didn't need them, he wouldn't spend the money on them. They have been used on cars and trucks since the fifties (at least).
From a retired auto mechanic.
 
I think NASA's statement is in error. When a helical spring lock washer is compressed to its crush height (squeezed all the way flat), it is still providing tension against the threaded assembly. This tension, along with the barbed or upset ends are what create the forces preventing the assembly from coming loose. There is a time and place where these fasteners are appropriate, and when not. They don't work as well (sometimes not at all) in situations where there is high vibration or oscillating tensions on the assembly. They can be permanently deformed by overtightening, or by heat. There's an entire armamentarium of ways to secure threaded fasteners.

Just downloaded the NASA doc and looked at it. Their diagram of using a jam nut is backwards(upsidedown). The jam nut should be installed on top of (after) the securing nut (which carried the torque/tension of the load). I wonder what else they got wrong?
 
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they don't work. the only style of lock washer that actually work are the cam style washers such as nord-lock.
 
sooner.boomer said:
I think NASA's statement is in error. When a helical spring lock washer is compressed to its crush height (squeezed all the way flat), it is still providing tension against the threaded assembly. This tension, along with the barbed or upset ends are what create the forces preventing the assembly from coming loose. There is a time and place where these fasteners are appropriate, and when not. They don't work as well (sometimes not at all) in situations where there is high vibration or oscillating tensions on the assembly. They can be permanently deformed by overtightening, or by heat. There's an entire armamentarium of ways to secure threaded fasteners.

Just downloaded the NASA doc and looked at it. Their diagram of using a jam nut is backwards(upsidedown). The jam nut should be installed on top of (after) the securing nut (which carried the torque/tension of the load). I wonder what else they got wrong?
Click to expand...

They're Rocket Scientists, not Mechanics, but considering that most of them have Engineering Degrees you would expect them to know better.:confused:
 
If they don't work, what causes that piece of scraped jagged steel on the bottom side of the hex nuts that always cut the crap out of my fingers???

Adrian
 
sooner.boomer said:
I think NASA's statement is in error. When a helical spring lock washer is compressed to its crush height (squeezed all the way flat), it is still providing tension against the threaded assembly. This tension, along with the barbed or upset ends are what create the forces preventing the assembly from coming loose. There is a time and place where these fasteners are appropriate, and when not. They don't work as well (sometimes not at all) in situations where there is high vibration or oscillating tensions on the assembly. They can be permanently deformed by overtightening, or by heat. There's an entire armamentarium of ways to secure threaded fasteners.

Just downloaded the NASA doc and looked at it. Their diagram of using a jam nut is backwards(upsidedown). The jam nut should be installed on top of (after) the securing nut (which carried the torque/tension of the load). I wonder what else they got wrong?
Click to expand...

The NASA evaluation is correct. Axial tension does not prevent rotation. If anything it enhances rotation when the assembly is vibrated. We, NASA, do not use them because of this. There are better alternatives.
 
Not appropriate for NASA - These will work on materials that can be compressed as they can maintain pressure. On a metal rocket this would not be the case.
 
TopRamen said:
They're Rocket Scientists, not Mechanics, but considering that most of them have Engineering Degrees you would expect them to know better.:confused:
Click to expand...

They need Howard Wolowitz, just like Sheldon, Raj, and Leonard did with M.O.N.T.E. in Big Bang.


Launching rockets (or missiles in my case) is so easy a chimp could do it. Read a step, do a step, eat a banana.

Sent from my iPad Air using Rocketry Forum.
 
JMZawodny said:
The NASA evaluation is correct. Axial tension does not prevent rotation. If anything it enhances rotation when the assembly is vibrated. We, NASA, do not use them because of this. There are better alternatives.
Click to expand...
How useful are they for providing correct tension on the bolt, which iirc improves ultimate strength?
 
They work once the fastener has loosened, but by this stage, some would have consider the joint to have already failed.
 
SpaceManMat said:
Not appropriate for NASA - These will work on materials that can be compressed as they can maintain pressure. On a metal rocket this would not be the case.
Click to expand...

A lock washer is not supposed to maintain tension or pressure itself, there are other things and ways to do that if needed such as selecting the correct materials and applying the proper torque to the fastener. Lock washers are one (poor) way to maintain the desired tension by preventing subsequent rotation of the fastener under load or vibration. We don't use them because they are ineffectual and often generate FOD. What is used depends upon the specific application.
 
Maybe someone could explain to a non-engineer how one of these is supposed to do ANYTHING to keep a nut in place. The washer itself has a perfectly flat surface area that is larger than the bolt, and seems like it would spin very freely compared to the nut. The tension seems to be pushing the nut to back off in the first place.

I don't see how these would be any help at all with applications involving metal parts.
 
For those of you who would like to download the manual titled "Fastener Design Manual" (.pdf format), you can get it here:

https://www.everyspec.com/NASA/NASA-NRP-PUBS/NRP-1228_127/

The genesis on how I even found this tidbit of info was when I was researching which washer would perform better (since I am a tad on the OCD side, wait it's CDO) for a simple screw switch. The funny thing is I still don't know what the best performing washer is in this application but, according to NASA, lockwashers are not the ticket.

I do remember when I was doing maintenance on A-10's I can't recall seeing many washers on the aircraft. There were screwed panels to be sure (I remember the cloth screw bags), but I can't recall washers. Elements that were subjected to severe vibration on the aircraft were safety wired (like the lead weights in the nose wheel well for CG distribution, based on the amount of 30mm ammo it was carrying).

Greg
 
10fttall said:
Maybe someone could explain to a non-engineer how one of these is supposed to do ANYTHING to keep a nut in place.
Click to expand...
I had always assumed that the upward force on the threads caused by the compressed spring of the washer would cause more friction on the upper side of the threads to prevent/reduce rotation and the rotational friction of the spring washer itself would reduce rotation once the bolt was loosened, but another comment here about the upward spring force causing even more loosening rotation of the bolt with vibration makes more sense.
 
Winston said:
I had always assumed that the upward force on the threads caused by the compressed spring of the washer would cause more friction on the upper side of the threads to prevent/reduce rotation and the rotational friction of the spring washer itself would reduce rotation once the bolt was loosened, but another comment here about the upward spring force causing even more loosening rotation of the bolt with vibration makes more sense.
Click to expand...

The common lock washers usually are either split ring or star versions. Both have a non-planar design with sharp edges that are supposed to bite into the thing being fastened and the head of the fastener to prevent them from rotating. If you torque them flat so the fastener is actually taking the load, the bite from the "teeth" goes away. Otherwise the lock washer is what keeps the force on the pieces being fastened together and there is really no good way to assess the performance of that system. You are holding things together with springs (although the screws themselves are also springs to some degree, but are more easily characterized, specified, and certified than are bits of twisted metal). You use screws for things that need to be taken apart occasionally and debris (FOD) is created every time you tighten or loosen a lock washer. NASA stuff is often subject to very high cleanliness requirements, so FOD is a big No-No.
 
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I just use thread lock compound. Locktite blue does wonders.


Sent from my Mobile Leash using the handy dandy Rocketry Forum app-thingy.
 
Need to be sure?
Nylock nut + Loctite red + safety wire + threads mashed with a hammer + good weld bead.

Not going anywhere!
 
Think of steel bolts not as solid objects, but as rubber bands.

They stretch. They have an elasticity range and a yield point, just like a rubber band. When properly torqued, they're near the center of their elasticity band, and it is friction that keeps them tight. Any "split-lock" will only serve as a flat washer.

The burrs are created when you remove it.

Split-locks don't "lock" anything.
 
I have a colleague who once worked on a project where his design specified aircraft-grade titanium bolts wired together. The fabricators were rushed and couldn't figure out where one would acquire such a thing (they were in Long Beach!), so they put in some stainless bolts and went for it. It apparently got to be a regular thing that someone would tighten the bolts every morning. Of course, it eventually failed. The engineer found a handful of bolts in the bottom of the remains of the assembly and asked the maintenance team why they weren't wired together.

The reply was that if they had been wired together it would have been a real pain to tighten them every morning.

Never overestimate your user.
 
wfcook said:
I have a colleague who once worked on a project where his design specified aircraft-grade titanium bolts wired together. The fabricators were rushed and couldn't figure out where one would acquire such a thing (they were in Long Beach!), so they put in some stainless bolts and went for it. It apparently got to be a regular thing that someone would tighten the bolts every morning. Of course, it eventually failed. The engineer found a handful of bolts in the bottom of the remains of the assembly and asked the maintenance team why they weren't wired together.

The reply was that if they had been wired together it would have been a real pain to tighten them every morning.

Never overestimate your user.
Click to expand...

Safety wire? We don't got no safety wire. We don't need no stinking safety wire! :y:

I love it. :rofl:
 

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