>The bit of tension in some dainty washer before the bolt is tightened means absolutely nothing.
Only if you restrict yourself to the "real engineering" that the internet loves.
>and the only possible reason that would ever be useful is if the application stayed in the operating area of that knee!
Which is frequently what happens when you try and build shit out of slip fit "what's the thinnest wall tubing we can get away with" held together with bolts acting as pins and the assembler is expected to just kinda eyeball it and not crush the tube lock washers are beneficial. We ship with nylocks now though because the extra part count is more expensive than the difference between nylock and split washer at our volume.
>There are devices in which a nut compresses a spring to a variable amount, like preload in suspensions, or resistance in exercise equipment and such. That is not a fastener application; it has nothing to do with locking.
This is just an argument of semantics/taxonomy. See also: belville washer or spring washer.
> build shit out of slip fit "what's the thinnest wall tubing we can get away with" held together with bolts acting as pins
There is your problem. However, even if you're consciously building for low quality, lock washers are still not useful or necessary. You will still have low quality if you remove them.
I think if you want to use a bolt and nut as just a pin that holds some slip tubing together, without unduly compressing the tubing, you want two nuts that are tightened against each other. The tubing likely has a bit of elasticity (likely, all the elasticity you would want from a washer and then some)*, so one nut can be lightly tightened against the tubing, so that the assembly doesn't rattle loose under ordinary movement of the product. There can be washers so you don't scratch the tubing, if that matters. Then you put on the other nut and tighten it hard against the previous nut, while preventing that one from turning any farther. This generates tension in the bolt section between the two nuts, binding them firmly together and preventing them from working loose.
This will cost you more in assembly time/steps and parts; that's what you get from building something that is less likely to fall apart in use.
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* It's entirely likely that the thin wall tubing has a much lower spring constant than a split lock washer. So that is to say, if you tighten the nut to the point that you're deforming the tubing, the washer may still be almost entirely uncompressed. Adding a relatively stiff spring into a "sandwich" that already includes soft springs generally doesn't do anything except past the point where the soft springs are fully compressed.
So finally we come to what you could have made clear from the start without the desultory, time-wasting back and forth. The industry in which you are involved and for which you would not consider hiring someone who believes objective data is one in which you imagine there is some benefit to lock washers in assembling crap.
It sounds as though you are using lock washers as a compliant element to avoid crushing fragile components rather than to prevent unscrewing - so outside the scope of this discussion.
Only if you restrict yourself to the "real engineering" that the internet loves.
>and the only possible reason that would ever be useful is if the application stayed in the operating area of that knee!
Which is frequently what happens when you try and build shit out of slip fit "what's the thinnest wall tubing we can get away with" held together with bolts acting as pins and the assembler is expected to just kinda eyeball it and not crush the tube lock washers are beneficial. We ship with nylocks now though because the extra part count is more expensive than the difference between nylock and split washer at our volume.
>There are devices in which a nut compresses a spring to a variable amount, like preload in suspensions, or resistance in exercise equipment and such. That is not a fastener application; it has nothing to do with locking.
This is just an argument of semantics/taxonomy. See also: belville washer or spring washer.