Roller pivots on production knives

[marrenmiller]

But the less contact area the greater force is being applied to the area of contact. If I have a pivot with 6 bearings per side the force of the liners pressing against the bearings is divided by six assuming equal distribution. If I have 12 bearings per side then that force is divided by 12.

In theory, surface area of contact doesn't affect the friction. It's just down to friction coefficient between the materials for the type of motion (rolling) and the force between the surfaces; F_f = (friction coefficient) x (normal force). Having more bearings just means proportionally less friction per bearing, which is equally offset by having more bearings in the first place.

 

[Lapedog]

Just FYI, not all real steel megeladons have the needle bearings. I have a 2017 full titanium one and it has ball bearings. It is still very smooth but I was kind of disappointed.

Yes, if you read my post you will see that I say not all of them have roller pins.

However I believe it is the new 2017 one thay has the roller pin bearings.

 

[marrenmiller]

While I'm not a mechanical engineer, I agree the advantage to rollers is lateral support. The drag created by the distance the roller is from the pivot would be imperceptible, or so I would imagine.

Yeah, the difference in drag (resistive torque about the pivot) should be proportional to how far out the average point of contact is, or to where the weighted average of the line or area of contact is. For a knife pivot, the difference would be tiny. The rollers should carry greater loads than a ball bearing, though.

Apparently there is a difference in friction coefficient between roller and ball thrust bearings, due to how the roller bearings have some built-in slip while turning about the axis of rotation.

 

[Wowbagger]

No, not reversed, the air ones can go faster, but we don't run them as fast. At full power I think the pneumatic ones can handle ~40k if I am not mistaken. (I'll check tomorrow, I don't like putting out vague info.) I can post some pictures of the "drill bit" too, basically just two small spinning blades.

Very cool. I would like that. My training is in industrial robotics but I didn't end up going that route and it has been a long while since.

 

[Lapedog]

While I'm not a mechanical engineer, I agree the advantage to rollers is lateral support. The drag created by the distance the roller is from the pivot would be imperceptible, or so I would imagine.

It is imperceptible. Its clear from knives with roller bearings that they do work in making a very smooth pivot.

Say again. This does not make sense to me.

I understand the idea of roller bearings looseing some efficiency when lined up radially. Ideally, they could use tapered rollers with tapered races.

I was drawing some diagrams of ball bearings and I think I was wrong. The blade would just swing out and the bearings would cause the washer capturing them to just pivot in the opposite direction of the blade.

So if the blade is coming out clockwise the washers will rotate counter clockwise around the pivot.

 

[Lapedog]

In theory, surface area of contact doesn't affect the friction. It's just down to friction coefficient between the materials for the type of motion (rolling) and the force between the surfaces; F_f = (friction coefficient) x (normal force). Having more bearings just means proportionally less friction per bearing, which is equally offset by having more bearings in the first place.

That’s what I was saying. That you will have the same force on six bearings per side or twelve. The ammount of force on each bearing will just be divided by the number of bearings. (Assuming equal distribution of force)

You put it far more eloquently than me though.

 

[marrenmiller]

That’s what I was saying. That you will have the same force on six bearings per side or twelve. The ammount of force on each bearing will just be divided by the number of bearings. (Assuming equal distribution of force)

You put it far more eloquently than me though.

Right, just trying to help clarify for the person you're responding to. You absolutely got it right the first time

 

[Wowbagger]

The drag in the rollers comes from having a greater surface area in contact with the surfaces of the blade and handle AND in contact with the retainer (the cage like thing that holds them in place and keeps them separated). Add to that grease rather than oil and one gets bunches more drag WHEN THE BLADE IS JUST FREE SWINGING.
The difference is one could stand on the side of them and pivot with like a body weight of 150lb and the roller bearing (probably) wouldn't be damaged because the contact area is so much greater (a line) where as with ball bearings the area of contact is very, very, small (a dot) (a point) and so the bearing surface will be dented (brinelled) from a similar massive over loading (body weight of ~ 150lb).

 

[Mo2]

The newest version has them on the full ti framelock. I am not sure about the liner lock or the “megalodon eclipse” which is the framelock with composite front scale.

I got a megalodon in a trade and my friend liked it so much he had to have it. It is an outstanding knife. Buy with confidence.

The Megalodon eclipse is on bearings and the Megalodon 2017 is on roller bearings.
Iirc real Steel and ruike have another model with roller bearings. Forget which ones.

 

[Mo2]

Some cheap and junky knives have rollers :

Which knife is this one?

 

[marrenmiller]

The drag in the rollers comes from having a greater surface area in contact with the surfaces of the blade and handle AND in contact with the retainer (the cage like thing that holds them in place and keeps them separated). Add to that grease rather than oil and one gets bunches more drag WHEN THE BLADE IS JUST FREE SWINGING.
The difference is one could stand on the side of them and pivot with like a body weight of 150lb and the roller bearing (probably) wouldn't be damaged because the contact area is so much greater (a line) where as with ball bearings the area of contact is very, very, small (a dot) (a point) and so the bearing surface will be dented (brinelled) from a similar massive over loading (body weight of ~ 150lb).

The amount of surface area has essentially nothing to do with the force of friction between two objects.

 

[craytab]

Some cheap and junky knives have rollers :

Is that a counterfeit?

 

[The Aflac Duck]

While I'm not a mechanical engineer, I agree the advantage to rollers is lateral support. The drag created by the distance the roller is from the pivot would be imperceptible, or so I would imagine.

Imperceptible, just like the rest of the bearing systems that are out there. We're talking about a knife pivot, not the bearings on an F1 car

I'm not pointing a finger at you, Chris. But it makes me laugh when people get all obsessed over what type of bearings are in their pivot.

When will people realize that the lockbar and detent are more important than the type of bearings or washers in their pivots?

 

[shinyedges]

Imperceptible, just like the rest of the bearing systems that are out there. We're talking about a knife pivot, not the bearings on an F1 car

I'm not pointing a finger at you, Chris. But it makes me laugh when people get all obsessed over what type of bearings are in their pivot.

When will people realize that the lockbar and detent are more important than the type of bearings or washers in their pivots?

This is true. Meh, it's a very specific hobby. It's to be expected for people to over analyze and make something out of nothing lol

Me, I'll use it. See how it holds up and works. If it works good, I'm happy. Doesn't work good, sell it and move on.

 

[The Aflac Duck]

This is true. Meh, it's a very specific hobby. It's to be expected for people to over analyze and make something out of nothing lol

Me, I'll use it. See how holds up and works. If it works good, I'm happy. Doesn't work good, sell it and move on.

Exactly. No need to write a book on such trivial things.

 

[b00n]

Imperceptible, just like the rest of the bearing systems that are out there. We're talking about a knife pivot, not the bearings on an F1 car

I'm not pointing a finger at you, Chris. But it makes me laugh when people get all obsessed over what type of bearings are in their pivot.

When will people realize that the lockbar and detent are more important than the type of bearings or washers in their pivots?

I think it comes with the "hobby enthusiast" territory, the more you're into the hobby the more you analyze every little detail. I mean some people care about the color of their model train conductors, we not so much.

But yeah, good washers, bearings whatever the type, if the detent is blah you can have SUPER AEROSPACE GRADE BEARINGS™ and they won't help. I always kind of hated that term "Aerospace Grade" such a marketing term.

The amount of surface area has essentially nothing to do with the force of friction between two objects.

That looks interesting, I have to read that later. It was a bit of a discussion point on a particular machine we had (something what only bolted down...at two points IIRC and the bolts sheared off) my boss doubted that it made sense, but one of the engineers argued that the friction between the steel and aluminium was enough to keep it in place.

 

[craytab]

Which knife is this one?

I think it is a counterfeit.

https://www.bladeforums.com/threads...0-delivered-direct-from-mother-china.1435427/

I'm no shiro fan but this is shameful.

 

[DocJD]

I think it is a counterfeit.

https://www.bladeforums.com/threads...0-delivered-direct-from-mother-china.1435427/

I'm no shiro fan but this is shameful.

Not the same knife , that one has ball bearings and not packed in grease . Evil but works fine . Thanks for remembering !

The roller bearing in green grease model was a real POS that had a detent that allowed the blade to sag open dangerously . Returned it long ago . But thanks for caring ! Just wanted to show the innards of a cheap knife with rollers which is thread topic .

 

[b00n]

Not the same knife , that one has ball bearings and not packed in grease . Evil but works fine . Thanks for remembering !

The roller bearing in green grease model was a real POS that had a detent that allowed the blade to sag open dangerously . Returned it long ago . But thanks for caring ! Just wanted to show the innards of a cheap knife with rollers which is thread topic .

Does it have a fuller on just one side? Looks that way. Kinda odd.

 

[Wowbagger]

The amount of surface area has essentially nothing to do with the force of friction between two objects.

I know what you are saying friction is independent of surface area.
But once you get lube in there, especially the grease that people insist on putting on bearings, then it makes quite a difference.
I believe someone mentioned you won't find roller bearings in a high speed assembly. They are for lower speed high load situations.
Ball bearings = high speed low drag.
And an air or oil wedge bearing even better so what we really need is to hook up our EDC to a pump or compressor for least pivot friction. Right ?
The gadget freeks are going to love this.