How do you determine pivot, stop pin and lock bar location?

Stew

Well-Known Member
With the triangle that's made between those three points on a liner / frame lock folder, what rules are trying to be followed as a course of best practice?

Is it best to aim for an isoceles triangle? Scalene? Equilateral? A right angle? Perhaps it doens't matter at all?

What other factors need to be looked at?

Presumably the stop pin is always set further back than the lockbar so that the blade tang will clear the stop pin on rotation.

It all has me wondering!
 

BossDog

KnifeDogs.com & USAknifemaker.com Owner
Staff member
Generally a triangle. That was the original concept by Michael Walker anyway as he explained it. In practice is not a perfect triangle but close and then modified just a bit here and there for looks.
 

Fellhoelter

Well-Known Member
Don't worry about the triangle.
Unless all 3 of your points are in line with each other, the triangle will be whatever it ends up being.
It may sound like blasphemy, but the triangle is almost meaningless.

What is important is how these points contact the blade.

For the stop pin, you want your point of contact to be at the tangent point of a radial line from the pivot.
And ideally have it contact in an arc shaped notch, not on a flat.
This maximizes the strength of the interface, and eliminates wedging.
Contact not at the tangent point allows for the blade to try and wedge itself and greatly increases blade movement due to wear.

Where the pin is doesn't matter.
In front, behind, whatever.
Distance from the pivot however is a factor.
Further away is better because of leverage, tang clearance, etc...

The lockbar is trickier.
Ideally, the same rule applies.
I'll describe a perfect lockbar.
One we can probably never attain in a normal sized knife.

As far away from the pivot as possible, and the lockbars axis tangent to the point of contact.
This way, all the force is applied along the lockbar, and isn't trying to lift it.

This is not practical though, so you just want to shoot for as close to that Ideal as possible.
As far from the pivot as possible, and the long leg cut as close to parallel to the tangent point as possible.
Contact should be a small patch at the "bottom" of the lockbar, and should be perpendicular to the long cut to avoid wedging there.

Clear as mud?

The thing I always try and picture is just where the force is being transmitted.
You want all force directed to the center of the stop pin.
You want to minimize the amount of force trying to lift the lockbar.
As a general rule, the further back a lockbar is, the worse.

Here are 3 pivots and lockbars to maybe clear it up a little.

lock geometry.jpg
 
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Fellhoelter

Well-Known Member
Here's an example of why "how" things interface are more important than "where" they interface.

This is a representation of 2 pivots and lockbars.

The point of contact is is exactly the same on the 2, but the axis of the lockbar is changed.
So, the "where" is the same, but the "how" is different.

In the first one, a lot of force is trying to lift the lock, and isn't pushing along the lock.

By rotating the axis of the lock, for lack of a better term, we direct much more of the force along the lock.

This is a good thing.

lockbar axis.jpg
 

Stew

Well-Known Member
Thankyou. :D

A bit for me to digest but exactly what I need.

The waters maybe muddy but the mud will settle and become more clear. :)
 

BossDog

KnifeDogs.com & USAknifemaker.com Owner
Staff member
Brian is a Blasphemer! :what!:
Kidding of course. He is giving some excellent advice here.

For those that don't know, Brian won the Tactical Folder of the Year award at the last Blade show. He should know what he is talking about.

I should have taken a bit more time to give a better answer. I read an interview with Michael Walker years ago and threw that bit out about triangles and should have mentioned his reasoning. His reason for the 3 point design was to ensure the lock forces were distributed to the maximum advantage. I don't want to mis-represent Walker due to a bad misquote or foggy memory of a 10 year old article.
 

Fellhoelter

Well-Known Member
Walker, Terzuola, and others have really pushed the triangle aspect.
An equilateral triangle being a very strong geometric shape.

This makes a lot of sense on first, second, and third look, but if you really start thinking about it, picturing the forces, and even drawing out examples, it doesn't hold up.

The triangle itself doesn't matter.

How, and where the points of contact are at, does matter.

Here's another sketch demonstrating a stop pin.

The circle in all 3 is the same. It's the distance between centers of the pivot and stop pin. The only thing changing is the rotation of that pin.
The force on a stop pin, with the knife open, is applied when there is pressure on the cutting edge, or from the lockbar.
Put pressure on the spine, and you are removing pressure from the stop pin, and putting it on the lock bar.
The only time there is pressure on both, is when the knife is static. Just open and sitting there. This is the main reason why the triangle doesn't mean anything.
Sure it's a very strong geometric shape, but in a knife, there is never any real force applied to all 3 points, which is what makes a triangle strong.

While cutting, pressure is removed from the lock, and put on the stop pin.

Any of these 3 stop pin positions will be equally strong, providing the material the pin is in has the strength to not deform.
It's a Class 1 lever and fulcrum, and the applied force and load is the same in all 3.
They look dramatically different, but in reality, the forces are all the same.

Providing of course that the contact point is on a line tangent to the stop pin and through the center of the pivot.
Change that point of contact, and a ton of other variables are introduced.

stop pin.jpg

A stop pin in any of these positions, or anywhere in that arc will be equally strong in this design.

So, you just have to work out where it will work best in any given knife design.
The further away from the pivot the better.
But where it's at, at least mechanically, means very little, providing you have your points of contact correct.
 
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Aikenn

Well-Known Member
With the triangle that's made between those three points on a liner / frame lock folder, what rules are trying to be followed as a course of best practice?

Is it best to aim for an isoceles triangle? Scalene? Equilateral? A right angle? Perhaps it doens't matter at all?

What other factors need to be looked at?

Presumably the stop pin is always set further back than the lockbar so that the blade tang will clear the stop pin on rotation.

It all has me wondering!
Holy molly. I have the exact same questions?????? Looking forward to the solution. I have a few working patterns if i can help you just ask. Really i am not like some who will not answer but just ask.
 

Aikenn

Well-Known Member
Generally a triangle. That was the original concept by Michael Walker anyway as he explained it. In practice is not a perfect triangle but close and then modified just a bit here and there for looks.
So there is no set optimal triangle????
 

Stew

Well-Known Member
Holy molly. I have the exact same questions?????? Looking forward to the solution. I have a few working patterns if i can help you just ask. Really i am not like some who will not answer but just ask.

Blimey, first time I’ve been here in ages and I find that an old thread of mine had just been bumped.

I still haven’t attempted a frame lock....
 

Aikenn

Well-Known Member
Walker, Terzuola, and others have really pushed the triangle aspect.
An equilateral triangle being a very strong geometric shape.

This makes a lot of sense on first, second, and third look, but if you really start thinking about it, picturing the forces, and even drawing out examples, it doesn't hold up.

The triangle itself doesn't matter.

How, and where the points of contact are at, does matter.

Here's another sketch demonstrating a stop pin.

The circle in all 3 is the same. It's the distance between centers of the pivot and stop pin. The only thing changing is the rotation of that pin.
The force on a stop pin, with the knife open, is applied when there is pressure on the cutting edge, or from the lockbar.
Put pressure on the spine, and you are removing pressure from the stop pin, and putting it on the lock bar.
The only time there is pressure on both, is when the knife is static. Just open and sitting there. This is the main reason why the triangle doesn't mean anything.
Sure it's a very strong geometric shape, but in a knife, there is never any real force applied to all 3 points, which is what makes a triangle strong.

While cutting, pressure is removed from the lock, and put on the stop pin.

Any of these 3 stop pin positions will be equally strong, providing the material the pin is in has the strength to not deform.
It's a Class 1 lever and fulcrum, and the applied force and load is the same in all 3.
They look dramatically different, but in reality, the forces are all the same.

Providing of course that the contact point is on a line tangent to the stop pin and through the center of the pivot.
Change that point of contact, and a ton of other variables are introduced.

View attachment 25696

A stop pin in any of these positions, or anywhere in that arc will be equally strong in this design.

So, you just have to work out where it will work best in any given knife design.
The further away from the pivot the better.
But where it's at, at least mechanically, means very little, providing you have your points of contact correct.
Very very clear thank. My tool making back round get me caught up in details.
 
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