Joe Anshien
TVWBB Platinum Member
I found this while going down a Quora rabbit hole. Then I searched some more and found other citations of the same. I had no idea that lockwashers seem to be ineffective (even detrimental) in preventing bolts from loosening. In researching multiple people from NASA to the USAF claim that they are not even used. If you want to secure you use Safety wire, cotter pins or self-locking nuts. Here is a link from Bolt Science (who knew there was a site Bolt Science?)
Interested in your thoughts and experiences on this.
David Lewinnek
20+ years engineering, mostly cars and factory equipmentUpdated 3y
What is an open secret in your profession that we regular folk don't know or generally aren't allowed to be told about?
Originally Answered: What is an open secret in your profession that us regular folk don't know or generally aren't allowed to be told about?
You know those extra parts in your Ikea desk that you spent hours searching for, the little lockwashers? Here’s the open secret: those damn things are useless, and the desk would probably have held together for longer if you hadn’t found them under the rug.
To the untrained eye, split ring lockwashers look like they will dig in and keep screws from loosening, but in reality they are as useless as, well, I actually can’t think of an example of anything as useless as these things. Maybe as useless as the percentage of argon in the air we breathe? As useless as a horoscope prediction from ten years before you were conceived? As useless as the caps lock on e.e. cummings’ typewriter? In a world with well-informed designers, rational users, and honest sellers of hardware, these would not exist:
I’m a cranky arrogant old guy, and I admit that I have a completely irrational dislike of split ring lockwashers and the young whippersnappers who don’t listen to me about them. It’s true that they (both the lockwashers and the young whippersnappers) offend my delicate sensibilities and make me swear a lot, but it’s not just me who thinks they are useless.
NASA administrators traditionally get unhappy when they have to send an astronaut up to tighten a loose screw on a satellite. For much less than the cost of a single manned rocket launch, they commissioned a study on fastener reliability, and made it available to the public as NASA Reference Publication 1228. Here is an excerpt:
There are some down to earth people at the American Society of Mechanical Engineers (ASME) who try to make people’s lives easier by releasing standards so that different nuts and bolts and washers are interchangeable. The section on split ring lockwashers in ASME B18.21.1–1999 says:
In conclusion, just say “No” to split ring lockwashers! Unless you’re German, then you can say “Nein.” Or if you’re Japanese you can say “Iya”. I don’t actually care what language you speak, just don’t use split ring lock washers, OK?
Update 8/28/2019: Several questions have come up multiple times in the comments. I’ll try to answer the most frequent questions here:
Q1: Why don’t they work?
A1: When you apply force to this kind of lockwasher, it becomes flat and the sharp edge is not pointed in a useful direction. When the sharp edge is pointed towards the nut or flange, there isn’t enough force to make it dig in. At no time during the screw tightening sequence do you get both the force and geometry needed.
Q2: Why were they ever used?
A2: James Watt built steam engines 49 years BEFORE Sadi Carnot first published the second law of thermodynamics. In the same way, threaded fasteners were used because they mostly worked, and were used long before the 1960s when we first developed a detailed theoretical understanding of why they worked. One unfortunate result of using bolts before we knew why they worked is that people thought split ring lockwashers would work, and by the time it was shown that they didn’t, their use had become customary. Also, they’re called “lockwashers” so one could be forgiven (although not by me) for assuming that they lock things in place.
731K views
10.2K upvotes
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546 comments
Interested in your thoughts and experiences on this.
David Lewinnek
20+ years engineering, mostly cars and factory equipmentUpdated 3y
What is an open secret in your profession that we regular folk don't know or generally aren't allowed to be told about?
Originally Answered: What is an open secret in your profession that us regular folk don't know or generally aren't allowed to be told about?
You know those extra parts in your Ikea desk that you spent hours searching for, the little lockwashers? Here’s the open secret: those damn things are useless, and the desk would probably have held together for longer if you hadn’t found them under the rug.
To the untrained eye, split ring lockwashers look like they will dig in and keep screws from loosening, but in reality they are as useless as, well, I actually can’t think of an example of anything as useless as these things. Maybe as useless as the percentage of argon in the air we breathe? As useless as a horoscope prediction from ten years before you were conceived? As useless as the caps lock on e.e. cummings’ typewriter? In a world with well-informed designers, rational users, and honest sellers of hardware, these would not exist:
I’m a cranky arrogant old guy, and I admit that I have a completely irrational dislike of split ring lockwashers and the young whippersnappers who don’t listen to me about them. It’s true that they (both the lockwashers and the young whippersnappers) offend my delicate sensibilities and make me swear a lot, but it’s not just me who thinks they are useless.
NASA administrators traditionally get unhappy when they have to send an astronaut up to tighten a loose screw on a satellite. For much less than the cost of a single manned rocket launch, they commissioned a study on fastener reliability, and made it available to the public as NASA Reference Publication 1228. Here is an excerpt:
You don’t have to trust just the fancypants academics at NASA, though. An unsmiling German guy named Gerhard Junker invented the Junker test to evaluate just how useless split ring lockwashers are, and that was back in the 1960s. Junker took a fastener, held two parts together with the fastener, and shook the assembly until it came loose. The results of the first Junker tests were that split ring lockwashers loosened about twice as fast as if they were not present. In other words, split ring lockwashers actively sabotage your assembly:
There are some down to earth people at the American Society of Mechanical Engineers (ASME) who try to make people’s lives easier by releasing standards so that different nuts and bolts and washers are interchangeable. The section on split ring lockwashers in ASME B18.21.1–1999 says:
Note that ASME doesn’t say that split ring lockwashers are used for locking anything in place. They do say that the springiness can compensate for developed looseness, but I have yet to see a situation where that is useful. The force from a split ring lockwasher is generally about 1% to 10% of the screw tension of a properly tightened fastener. Once the tension has gone down by 90%, the joint has generally failed even if there is a forgiving spring to account for that last 10%. In fact, most of the time I would prefer to hear a rattle if my joint tension has changed by an order of magnitude or two.
In conclusion, just say “No” to split ring lockwashers! Unless you’re German, then you can say “Nein.” Or if you’re Japanese you can say “Iya”. I don’t actually care what language you speak, just don’t use split ring lock washers, OK?
Update 8/28/2019: Several questions have come up multiple times in the comments. I’ll try to answer the most frequent questions here:
Q1: Why don’t they work?
A1: When you apply force to this kind of lockwasher, it becomes flat and the sharp edge is not pointed in a useful direction. When the sharp edge is pointed towards the nut or flange, there isn’t enough force to make it dig in. At no time during the screw tightening sequence do you get both the force and geometry needed.
Q2: Why were they ever used?
A2: James Watt built steam engines 49 years BEFORE Sadi Carnot first published the second law of thermodynamics. In the same way, threaded fasteners were used because they mostly worked, and were used long before the 1960s when we first developed a detailed theoretical understanding of why they worked. One unfortunate result of using bolts before we knew why they worked is that people thought split ring lockwashers would work, and by the time it was shown that they didn’t, their use had become customary. Also, they’re called “lockwashers” so one could be forgiven (although not by me) for assuming that they lock things in place.
731K views
10.2K upvotes
173 shares
546 comments
