Advantages and Disadvantages of 3 common locking methods for folding knives

From L-R Liner Lock, Axis Lock and Lock back folders.

Currently there are 4*** general locking mechanisms employed on todays folding knives.

In no particular order:

1) The Liner Lock, whereby a section of one liner, is treated to produce a "spring mechanism" in order to engage with the rear of the knife tang.

Liner lock, showing precise engagement of the locking liner

2) The Axis or Roller lock Mechanism

The axis or roller locking method, whereby the blade is locked by the action of a "bar" under spring tension, engages with, or moves over the rear end of the knife tang. The blade is held in place as pressure upon the bar is not directed towards releasing the bar, hence only a relatively small weak spring is required to hold the bar from moving. Although any slight movement could cause a catastrophic closure!

Axis lock, note the partially visible spring attached to the "roller bar"

3) the Lock Back mechanism

 The traditional lock back mechanism. This mechanism has been around for some time and the locking is achieved when a notch in the tang of the blade engages with the opposing notch in a (usually) thick bar, which is also a spring and forming part of the knife body itself. The sides of the knife are in direct contact with the knife's liners (as is the case for non-locking folders for example, Swiss Army type folders etc

Traditional "lock back" note the notch (covered in grease, facing viewer) which forms part one of two of the locking mechanism

A traditional lock back folder, the blade is in direct contact across it's full surface with the knife liners.  

The blade on this axis locking folder is not in contact with the liners but only the surface area of the washers, in this case for this knife, a plastic and brass washer.

On this liner lock folder the blade is like that of the axis locking knife, only the blade is in contact with the washers, not the entire knife liners.

ADVANTAGES

The advantages of 1)

Quick to open one handed, relatively simple design.

Can be designed as a "flipper" for super fast operation.

Design lends itself for Rescue knife design, ie one handed operation.

The advantages of 2)

quick to open

left or right hand operation

Design lends itself for Rescue knife design, ie one handed operation.

The advantages of 3)

Left or right handed operation.

Large surface area of blade in contact with actual knife body

Few parts and therefore less affected by ingression of foreign bodies into mechanism.

Wearing of parts in direct contact with each other is slow.

Almost zero field maintenance or no user serviceable parts.

Spring tension is usually high and that means blade retention within the knife body is good.

DISADVANTAGES

Disadvantages of 1)

Because of the gap created by the spring liner foreign material can enter here, such as sand, mud or sticks etc and render the mechanism inoperable unless cleaned.

Knife is only "handed" ie for a right hand closure, the liner that moves must be on the left hand side as viewed when looking at the open knife tip uppermost. The a left hand closure, the spring liner must be on the right hand side as viewed similarly.

The rear of the knife, ie tang is only in contact with washers (plastic or metal or a combination of both). This means the knife body plays no part in stabilizing any lateral forces exhibited upon the blade. 

Once washer/s wear sufficiently, then the knife will require servicing. This is an almost impossible task to perform in the field as it requires small screw drivers or torx head drivers or the like to be carried in order to strip the knife and replace the washers.

Indent setting plays large role in blade retention in the closed position- depends on the manufacturer.

Washer tension must be set right in order for proper operation.

Disadvantages of 2)

Locking mechanism's weakest link is the small spring. If this fails (it will have a limited lifetime of operation), then the knife can not be closed or locked safely.

The axis system,  is open to ingression of foreign matter rendering the opening and or closing to be impossible until the material is cleared. 

This knife design sports the greatest number of small parts. The more parts the more things there are to fail.

Sudden Vibration forces greater than the holding force of the roller spring can actuate the roller and cause disengagement.

Depending on the strength of the roller spring, the blade can come out of it's enclosure if subject to a downward force (such as falling tumbling etc).

Spring tension is usually weak and blade retention within (closed position) is just OK.

Washers will wear out and require service, small parts can be lost in the field. Field servicing not advised.

Washer tension must be set right in order for proper operation.

Disadvantages of 3)

Due to a larger surface area of blade tang in contact with steel liners, there is more friction generated and a requirement for adequate lubrication is a must for smooth long life time operation. Failure to do so can wear parts which are not user serviceable or possibly serviceable by the manufacturer.

*If the spring back is not sufficiently strong then pressure against the locking mechanism opposing the lock can cause the lock to fail or if the notches are not deep enough (only seen on poorly designed lock backs).

2 hands are generally required to open the knife. Although it is possible for one handed opening.

* any poorly designed versions of 1) or 2) can also suffer unexpected closure.

***A quick note on Frame Locking knives.

I don't mention Frame Locks as I think this is a poor design compared to the above knife designs. I'll explain in another blog why but briefly, poor lock up first time, as it is vey difficult for manufactures to get the correct springiness within the same part of the knife which serves as part of the body of the knife. Also if manufacturers use materials for scales which do not possess good properties for springs and other smaller parts are required.   

I'll also say why the marketing guys have you believing otherwise.