Ball Bearing pivots actually weaker than PB washers?

Lapedog said:
I never understood the idea of roller pin bearings arranged in a circle around the pivot like that. Because the part of the pin closer to the centre of the pivot will have to roll slower than the part of the same roller pin that is further from the centre of the pivot. That means the part of the pin further from the centre will be dragging since it has to move a further distance in the same ammount of time.

I’m not a physicist so there is probably some logical fallacy that I am not getting.
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I'm not qualified , either . But , wheels can turn corners . Bumblebees can fly . The very expensive Russian maker probably knows something we don't .
 
The very expensive Russian maker knows that a lot of people have excess money that the maker would like to take from them.

Coming next; differential bearings for those worried about scuff.
 
Lapedog said:
I never understood the idea of roller pin bearings arranged in a circle around the pivot like that. Because the part of the pin closer to the centre of the pivot will have to roll slower than the part of the same roller pin that is further from the centre of the pivot. That means the part of the pin further from the centre will be dragging since it has to move a further distance in the same ammount of time.

I’m not a physicist so there is probably some logical fallacy that I am not getting.
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Pretty logical for someone who is not an expert. IF you look at typical thrust bearings you will see the outside diameter is a bit bigger to compensate for exactly what you are talking about. Problem is that you cannot do that for totally flat bearing. It would make the assembly to thick. With knives it isn't a big deal because the rotation is minimal. 180 degree rotation max.

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Either the inner side of the roller rod will skip by "braking", or the outer side will skip by "accelerating". Possibly a bit of both all the way through. There is no rubber here to take up the slack, so it definitely is pure friction that will take over, at least in a part of the roller...

I guess the rollers (for a flat-type pivot) should be split in 2-3 short portions, as long one-piece rollers don't make a whole lot of sense, friction-wear wise...

Gaston
 
I can easily imagine some huge honking thick tank knife equipped with THRUST bearings . Even sounds cool ! :cool::thumbsup:
 
Nope, simple physics

The further out from the center of a rotating circle the greater the distance travelled for a given degree of rotation
 
My concern with bearings is the open windows for grit that comes along with the prospect of a folding pocket knife.
 
Cobalt said:
Yes, but it would make a knife unworkably thick. Think of a skateboards bearings which are sealed cartridges and they are at least 1/4" thick. That would make for a very thick knife.
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There's probably a way to scale down that thickness some ? Anyway somebody must buy those tank knives . Medford and such .
 
My 909 has been dropped in mud, kept in a pocket that constantly fills with dirt, and denied oil for weeks at a time.

Never an issue with the bearings locking up. I might give the pivot a rinse if it gets caked, but the 909 works regardless.
 
DocJD said:
If it's so dang "simple" , then what is your answer ?o_O (Assuming lateral stress or whatever you like) .
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Not having made a study, I don't know. Not having used a roller bearing knife, I don't even have an opinion. But the question was "which is stronger?".

I don't have an answer but I am curious what the answer is. Unlike some folks here, I don't know or pretend to know everything. ;)

shinyedges said:
I don't think even if he said one over the other it would have any more validity than any other opinion.
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See? That's what I said. Nobody is even trying to answer the question but all kinds of verbal gymnastics are being presented just to avoid an actual answer.

I'm guessing nobody wants to know the answer.

I'm out.
 
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singularity35 said:
Not having made a study, I don't know. Not having used a roller bearing knife, I don't even have an opinion. But the question was "which is stronger?".



See? That's what I said. Nobody is even trying to answer the question but all kinds of verbal gymnastics are being presented just to avoid an actual answer.

I'm guessing nobody wants to know the answer.

I'm out.
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How the hell can we decide an answer with out actually conducting tests to know which is stronger?

Extreme side loads will likely cause damage to a washer, they are not crush or deformation proof. Hell I don't know, the answer is a usual.. it depends lol

Even if a washer is crushed or damaged the knife will likely still function, same as if the bearings indent the titanium the knife is still functional.

I see the Philippines is getting hammered with a storm on the news. Hope you and yours are well.
 
shinyedges said:
How the hell can we decide an answer with out actually conducting tests to know which is stronger?
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I guess that's the bottom line. I'm still curious though.

shinyedges said:
Extreme side loads will likely cause damage to a washer, they are not crush or deformation proof. Hell I don't know, the answer is a usual.. it depends lol

Even if a washer is crushed or damaged the knife will likely still function, same as if the bearings indent the titanium the knife is still functional.
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Another question for that is which of them will fail sooner with the same amount of damage.

shinyedges said:
I see the Philippines is getting hammered with a storm on the news. Hope you and yours are well.
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Yes, it was headed our way but luckily we dodged the bullet when the track changed almost at the last moment. The storm killed around 100 people at last count.
 
singularity35 said:
I guess that's the bottom line. I'm still curious though.



Another question for that is which of them will fail sooner with the same amount of damage.



Yes, it was headed our way but luckily we dodged the bullet when the track changed almost at the last moment. The storm killed around 100 people at last count.
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I'm curious too, I have both washer and bearing knives. But I'm not going to destroy one of my bearing or washer knives for this thread. So, opinions will have to do :p

Good to here it changed course, I'm from Florida and grew up with hurricanes. The news/weather people can predict the path to an extent but big storms are unpredictable.

I've seen first hand what a roof ripped off is like.
 
Cobalt said:
Melt? at the speed with which someone opens a folder I do not think you need to worry about melt or soft vs hard. Bearing systems move easier, with less friction, hence their use. Bushing systems take heavier loads with more friction, hence their use in suspension systems. Look under your car or truck and the majority of partial rotating/pivoting components have bushings not bearings. The can take much higher loads due to the flat surface area having much larger force distribution. A ball bearing system would likely be destroyed by suspension loads due to high point stresses on the ball bearings.

Hardness is irrelevant when you have a flat piece against a slab of handle against a blade flat. It is like a sandwich with layers all pressed against each other. A bearing system has bearings with a single point on each ball bearing touching the surface area. Force is much more evenly spread on a bushing than it is a ball bearing system or even cylindrical bearings. Just simple statics. Each ball takes one point load and the overall force is distributed over however many ball bearings you have.

In a knife's case, I don't think there is much of a difference, but there is no doubt that the load on a bushing is distributed more evenly over it's larger surface area than a ball bearing system.
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This sound most plausible to me . So my "simple" WAG answer to the OP = YES !
 
Correct me if I'm wrong but I thought the whole point of bearings or washers in a knife is for smoother opening. I can see how it can be a weak point in a knife design. I feel as though the blade would break before a washer/bearing fails.
 
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