Knife Locks, part 1

A folding knife has to combine a number of opposing characteristics. It should not swing open suddenly or close unexpectedly, but at the same time it must be able to operate smoothly. This is not an easy combination. There are various ways of controlling the movement of the blade. It can be a simple spring which provides resistance or a mechanical lock. These locks come in all shapes and sizes. European Blades Mag. will discuss the most important ones in a number of episodes.
 
Text: Bas Martens
 
Let us begin with a disclaimer: as the title implies, European Blades Mag. Is about European knives and knife makers. Yet in preparing this series, we found that most locking mechanisms are American inventions. So do not be surprised if you see the names of several famous American knife making companies. And please let us know about any European locking mechanisms which are not mentioned here.
In order to describe the different locking mechanisms of folding knives, we have to begin with something that is not a real locking device: the slip joint. It all starts with a long spring which, due to its own elasticity, offers some resistance against the unintentional opening of a blade. In France, where this construction is quite popular, there are two main versions: the 'cran carré' (or 'cran plat') and the 'cran forcé’. The first is a regular slipjoint, the second might be called a notched slipjoint.
The difference lies in the shape of the back of the blade. With the normal slipjoint, the spring lies on the flat spine of the blade. On the notched slipjoint the spring has a notch which falls into a recess in the blade spine. The shape of the blade is such, that it pushes this notch upwards upon closing, thus giving an extra resistance.

 

     

 

 

A modern version of the notched slip joint was developed by British knife maker Mike Read, as shown here on the Spyderco PITS. Long machined slots at the top of each handle scale create integral spring arms that are connected by a hardened pin, which acts as the notch and applies pressure on the tang of the blade to stabilize it in the open position. Another creative solution was designed by Belgian knife maker Maarten Strykers. His folding Puukko is a slip joint variation, with a detent ball in the titanium side of the handle.

 

 

 

In all these models, the spring isforced out of the way by the movement of the blade. Then somewhere, someone came up with the idea that you could hinge the spring. If it was pushed down at the rear, the notch would be raised. And if you then put that in a folding knife, you have a back lock. Or lock back. Or mid lock, which some call a front lock - but that's about it.
Who should we give credit for this idea? We have not been able to find the answer. It seems that over a fairly long period of time, a lot of people had similar ideas. Not one 'Eureka', but a gradual development.
A construction which strongly resembles the modern back lock can already be found one hundred years ago, in a patent for a folding axe by the American Martin E. Seely. That axe, by the way, would not look bad today either. Figure 3 of Seely's patent drawing shows the construction: an arm (19) with a locking cam (17) on one side and a pawl (18) on the other side which has to be pushed down to unlock the axe head. But to be honest: there are dozens of patents with more or less similar constructions.

 

The drawings accompanying Martin E. Seeley's 1916 American patent for a folding axe.

Figure 3 shows his version of a back lock.

One thing is certain, the back lock mainly got is popularity through Buck. In 1964, the American company presented the 110 Folding Hunter, a folding knife with the rigidness of a fixed blade. This was mainly due to the back lock. At the very back of the handle there was a recess to depress the rear of the locking arm. The 15 million copies that have been made of the 110 have made the lock popular worldwide.

 

can be pushed down. The front hinges up, and the blade is unlocked. (Illustration by Kershaw)
 

But what is the real name of this lock? In practice, the names back lock and lock back are used interchangeably. We asked several manufacturers about it, but nobody had a satisfactory answer.
Over the years, numerous variations on the back lock have emerged, with changes to both the front and rear end. To start with the rear: several knife makers have shortened the arm. As a consequence, the recess in the handle for pushing down the arm, had to be moved to halfway along the back of the knife. Some manufacturers call this a mid-lock and some even call it a front lock, like Spyderco with its Sage 4. It just depends on where exactly the recess in the handle back is located.
On the other hand, some knife makers have extended the arm. On the EKA Swede T9, shown here, the arm protrudes from the back of the handle to form an eyelet for a lanyard. Pressing it down unlocks the blade.

 

    

At the front end, there have been many small changes in the shape of the notch, the corresponding recess in the blade spine and the contact points, sometimes with an extra pivot, spring or pin. More often than not, these are invisible from the outside, and not all knives come apart easily. But sometimes a manufacturer advertises its modifications, like the American Cold Steel company with its own variant, the Tri-Ad Lock.
The Tri-Ad Lock is a variant of the back lock. Cold Steel is extremely proud of it. There are numerous videos on YouTube proving the strength of the lock. However, Cold Steel had come very close to missing the boat.
As far as we could find out, the story went something like this:
Cold Steel's in-house designer, Andrew Demko, came up with an improvement to the back lock mechanism in 2006/2007 - we will discuss the technical details later. He applied for a patent in April 2007, with himself as the inventor and Cold Steel as the owner of the patent rights. While the application was pending, an American knife maker, John W. PerMar Jr. contacted Cold Steel with a new mechanism he had just patented. The essence of both inventions was almost identical.
Couldn't Cold Steel have known? According to Demko it could not, because during his research PerMar's patent had not yet been granted. It was an awkward situation. But there is a solution for everything. Cold Steel pulled out its wallet and paid PerMar an unknown sum for his patent. Subsequently, Demko's application was slightly modified and patents were granted in 2008. The same year, the new Tri-Ad Lock was introduced, starting with the Cold Steel American Lawman and Espada Series. Today, PerMar even gets a piece of the credit. Cold Steel calls the Tri-Ad Lock "a successor to a patented lock design originally created by the very talented John PerMar." A bit of immortality after all.

 

    

The first page of drawings of Andrew Demko's 2008 patent (left) and John PerMar's 2007 patent.

(United States Patent Office)

So what is it all about? Basically, it is all about a transverse pin. As described, the back lock (Cold Steel calls it a rocker lock) consists of a spring-loaded arm with a notch which falls into a recess in the back of the blade. In the Tri-Ad Lock, the recess is made somewhat longer and, before the notch, there is an additional cross-pin between the two halves of the handle. This cross-pin does a number of things. Firstly, it acts as a stop pin. It limits the movement of the blade and prevents it from opening any further. This is an extra, because with most back lock folding knives this is done by the notch of the lock.
In addition, the pin plays an essential role when applying upward or downward force on the blade. With an upward pressure the blade is forced to open further. This is not possible because the blade lies against the stop pin. This in turn lies against the front of the rocker lock, which in turn lies against the thr back of the blade. So the forces on the blade are distributed instead of being concentrated at one point.

 

 

    

A Cold Steel Code 4 with Tri-Ad Lock, respectively closed, and almost fully opened.

The same applies to a downward force on the blade. The back of the blade pushes against the rocker lock, which lies against the stop pin, which in turn distributes the forces between the frame and the other parts of the Tri-Ad Lock - physicists could probably devote many pages to this. Here, it suffices to say that it works, but don't ask us how much abuse the Tri-Ad Lock can withstand. The description in Demko's patent is perhaps the most honest: it calls the stop pin a 'safety pin'.
From the description it will be clear by now that the Tri-Ad lock has to be made precisely. The fit of the blade, stop pin and notch is a very precise affair. This is the reason why Cold Steel knives with the Tri-Ad Lock often have to "run in" for a while. With new knives, especially the opening can be very stiff.
Finally, another aspect: the axis of the rocker lock lies in a slightly oval opening, so that it has a little slack in the longitudinal direction. The rocker lock can therefore adjust itself to possible wear and tear of the lock.

Linerlock
The most common lock mechanism on folding knives is probably the locking liner, or the liner lock. A liner lock folding knife almost always has a handle of two thin metal plates (the liners) to which the handle scales are fastened. One of the liners is split at the front so that the front piece is divided into two parts. One of these pieces is slightly bent inwards. Thanks to the elasticity of the material, it works like a leaf spring.
When the knife is folded, the spring rests against the side of the blade. When the knife is fully unfolded, the spring can move further inwards and lies against the back of the blade. This way, the spring blocks the movement of the blade. In order to close the knife, the spring must be pushed aside until the blade can be folded. It seems simple, but it is not. The modern liner lock is an extremely ingenious construction. This is thanks to knifemaker Michael Walker. But first we have to go back in time.
The forerunner of the modern liner lock was invented over a hundred years ago by the American knife maker William Franklin Watson from Tidioute, Pennsylvania. Watson patented it in July 1906, together with Roy Chadwick from the same town. Both men worked at Brown Brothers' Union Razor Company at the time, but Watson's invention was used under licence by another company, the Cattaraugus Cutlery Company of Little Valley, New York. The exact circumstances for this are not known. Until the patent expired in 1923, Cattaraugus appears to have been the only company making liner lock knives (although the term did not exist at the time). After that, this method of locking knives became more widespread.

 

    

The current popularity of the liner lock is due to the American Michael Walker. Walker started making knives around 1980. Initially these were fixed blades, but as Walker apparently hated making scabbards, he soon specialised in folding knives. In the process, he proved to have a special talent for technique. One of his inventions was an improved liner lock.
In Watson's original patent, the locking point lies in front of the blade axis. Therefore, the spring runs along the axis of the knife which means that only a small part of the liner can be used for the lock. In addition, the spring does not lie against the back of the blade but in a small recess and protrudes outside the handle.
Most folding knives have a spring in the handle spine, which prevents the blade from opening by itself. The first thing that Walker did was to remove this spring. This allowed him to move the liner lock behind the axis, which meant it could rest against the back of the blade, with a much larger contact area.
Furthermore, Walker put a ball detent in the side of the spring. When the knife was closed, the ball fell into a recess in the side of the blade, thus providing sufficient resistance to prevent accidental opening. At the same time, the little ball gave less friction when opening and closing the blade.

 

This is what a modern liner lock looks like: the liner is partly sliced through and bent slightly inwards.

semi-circular trace of the ball can be seen on the blade and ends in a small hollow.
 

 

        

The position of the liner lock with the blade  partly folded in and fully opened. In the latter position the liner lock

moves behind the blade.
 

Finally, Walker made a small but crucial change: he bevelled the back of the blade. This made his liner lock self-regulating. If the back of the blade or the spring were to wear slightly, or if the blade had a little more play, the spring would simply slide in a little further and the lock would remain intact.
Walker made his first knives with this mechanism in the 1980s, usually in combination with a single-handed opening blade. In 1989, he received a trademark on the word liner lock. For a long time, knife makers were only allowed to use this term with his permission. According to the US register of trade names, that registration expired in 2013.
In all its brilliant simplicity, the liner lock has become enormously popular. The way in which the spring is bent and the bevel of blade and spring differ from manufacturer to manufacturer, and even in different models from the same manufacturer. To date, no one has been able to substantially improve the mechanism.

 

 

 

Three knives with different liner lock safeties. From top to bottom: the CRKT No Way Out,

the Extrema Ratio MF0 and the CRKT M16-O3Z.

In normal use, the liner lock is a wonderful, simple and safe system. In exceptional cases, however, the liner lock may be pushed aside accidentally, causing the blade to close. This is more likely to happen if, over time, play occurs due to wear on the back of the blade or the front of the liner lock. It is hardly likely, but Murphy's Law is always lurking.
As a solution to this 'problem', several knife manufacturers have come up with an additional safety: a lock locking device. The two main companies in this field are Extrema Ratio and CRKT.
Some Extrema Ratio models have a ‘safety catch’ on the right side of the handle, consisting of a circular steel plate with an inwards protruding cam. When the catch is pushed forward, the cam rotates against the side of the liner, which now cannot be pushed aside.
The pawl can only be turned forwards when the blade is open. The word 'LOCK' then becomes visible. In order to close the knife, the safety catch must be turned backwards. The liner can then be pushed to the side and the blade folded.

 

The Extrema Ratio has a safety catch on the right handle. That safety is a circular steel plate with a

notch sticking inwards. When the blade is on safe, the notch blocks the liner lock.
 

CRKT came up with the Lake and Walker Knife Safety (LAWKS) in 2000: a pin that blocks the lateral movement of the liner. In 2006 followed the AutoLAWKS, which is basically the same mechanism, but then automatic. The safety catch, again an L-shaped plate, it is now under spring pressure.
When the blade is opened, the liner springs inwards. The safety catch can now be moved forwards until its notch lies against the side of the liner, blocking its movement. In order to close the knife, the safety catch in the right-hand side of the handle must be pushed back. The safety notch pivots downwards, and then the liner can be pushed aside and the blade folded in.

 

      

Left: The safety catch of the AutoLAWKS mechanism on the CRKT M16-O3Z. 
Centre and right: The AutoLAWKS mechanism also has an inward-facing cam. The photo with the liner

shows how it lies under the liner lock, blocking it.
 

The disadvantage of the LWAKS and AutoLAWKS mechanism is that it requires two hands. One hand has to operate the safety and liner, the other has to fold the blade. CRKT has come up with a solution in the form of the Ikoma Lock Safety, or ILS.
With the ILS system, the liner lock is no longer located at the top of the handle, but on the liner itself. It is again a hinged plate with an outward projecting cam. When the blade is closed (or partially opened) the cam rests against the edge of the handle scale. If the blade is opened completely, the liner with the ILS moves inwards. Under the influence of its own spring, the plate with the cam rotates between the liner and the handle and, voilà, the liner is blocked.
To close the blade, the thumb presses down on the ILS and pushes liner and ILS aside; the index finger folds the blade.

 

    

The two positions of the CRKT Ikoma Lock Safety. In the right photo the blade is partially opened and the cam

springs inwards. The liner cam rotates downwards and now lies between the liner lock and the handle.
 

 

 

The Reeve Integral Lock
The Reeve Integral Lock, better known today as frame lock, is a further development of the liner lock.
Opinions differ as to the original name. Some say the invention was launched as Sebenza Integral Lock, others say it was Reeve Integral Lock from the beginning. However that may be, both designations refer to the same mechanism. The inventor is Chris Reeve, who first used this lock on his Sebenza folding knife. The prototypes seem to have been made as early as 1987, but the Sebenza was launched in 1991, so the knife and the lock are celebrating their 30th anniversary this year. The Sebenza is still in production and is a classic in more than one respect: for its exemplary fit and finish, the use of superior materials, and of course for its locking mechanism.
Like most good ideas, the Reeve Integral Lock is a marvel of simplicity. Of course, Chris Reeve was familiar with the Walker liner lock. Since it is part of the liner, the spring plate in the handle is rather thin. This limits the strength. So wouldn't it be convenient to use the whole strength of the handle as a lock?
A nice thought, but Reeve's idea was not so easy to realise. A little experimentation came up with the solution: a cut-out in one of the metal grip halves that acts as a spring pressured lip.
To achieve this, the lip must be pre-bent during production so that it constantly pushes inwards. This cannot be done with 3 mm thick metal, so the bending point has to be made thinner. It sounds simple, but it is a technical tour de force. The milling of the bending point, the heat treatment, and the degree of bending all require careful consideration. Chris Reeve finally succeeded and since then the Reeve Integral Lock, or frame lock, has become a household name.

 

   

This is one of the more recent versions of the Sebanza.
 
When the blade is open, the frame lock, as stated, lies against the back of the blade. During the opening and closing movement, it pushes against the side. In order to reduce the friction, the frame lock contains a small detent ball. This ball ensures that the blade can be opened smoothly.
The frame lock has a number of advantages over the liner lock. The part that locks the blade is much thicker and can therefore withstand much greater stress. It is therefore mainly used for knives that are used intensively.
The frame lock also has disadvantages. The materials of the frame and blade must be carefully chosen and preferably have a similar hardness - otherwise one of them would wear out more quickly.
Another aspect is the design. As the name suggests, the frame lock is part of the frame (the handle) of the knife. Unlike the liner lock, which is almost always covered by the handle scales, it is a visible part of the construction. Of course, this does not mean that the frame lock results in ugly knives, on the contrary. Take for instance the elegant LionSteel TiSpine: solid and beautiful. Numerous custom knife makers have made beautiful frame lock knives as well.

 

Followers
After its introduction, the Reeve Integral Lock was quickly copied. This was possible without problems, because Chris Reeve had protected only the name, and not the design itself. According to a comment made by his wife Anne in 1999 on Knifeforums, there were two reasons for this. Reeve thought he could make the best frame lock himself and was not afraid of competition. Secondly, he was not keen on the complicated and costly patent procedure.
One of the first imitations was the Benchmade 750 Pinnacle, which tried to imitate the Sebenza in several ways. It was a good knife, but friend and foe alike agree that the Pinnacle was no match for the Sebenza in terms of finish and quality.
Benchmade has developed a number of its own locks over time, but still uses the frame lock. The pictured 755 MPR Sibert from 2010 (now no longer in production) has an interesting variant. At the front it is a pure frame lock, but the spring lip is narrowed at the rear and looks more like a liner there, covered by a half handle scale. The milling of the lip is not on the inside, but on the outside. It is a kind of hybrid solution. Another special feature of the 755 MPR Sibert is that the lip lies not completely behind the blade. It has a protruding edge which limits its sideways movement. Why is not quite clear. Maybe it is just cosmetic, maybe in case of extreme wear the edge prevents the lip to move completely behind the blade, making it difficult to push aside.

 

  

Close-up of the frame lock on the Benchmade 755 MPR Sibert. It is a kind of hybrid solution, as half of the

lock is under the handle. Note also the protruding edge on the lip, which falls over the side of the blade.
 

Spyderco also makes various models with the Reeve Integral Lock. Spyderco is one of the few companies that gives full credit to the inventor. In the catalogues and the accompanying 'Edge-U-Cation' note with each knife, Reeve is mentioned in full. The Sage series, an homage to different locks, of course also has a Reeve Integral Lock model, the C123TIP Sage 2.
The Sage 2 has the original locking mechanism, but in some later models Spyderco has made some changes. The friction between the steel blade and the titanium lip has led to a separate steel friction piece on the front of the lip, which should prevent wear.
With a good frame lock, the wear does not matter much. The contact surface of lip and blade is usually slightly bevelled. This means that the frame lock can hinge further in when worn and actually block the blade even better.

 

Additional safety
As with the liner lock, there are frame lock knives with an additional safety - a lock locking device. The CRKT Williams Otanashi no Ken pictured here has the Lake and Walker Knife Safety (LAWKS) discussed above: a pin, which in this case blocks the sideways movement of the frame lock. When the blade is opened, the frame lock springs inwards. Then, a small pallet at the top of the right handle can be pushed forward. An attached cam pivots backwards, blocking the sideways movement of the frame lock. The construction is neatly concealed behind a round plate around the axis of the blade.

 

    

projecting cam blocks the frame lock.
 

Italian LionSteel has developed the RotoLock. It is a rotary knob in the right-hand side of the handle, with an inward projecting cam. When the knife is unfolded, this cam can be turned in front of the frame lock, again blocking the lateral movement of the frame lock.
 
In the next episode, we will discuss the Benchmade Axis lock, the CRKT Fulcrum Action, the Spyderco Compression Lock and the Benchmade Nak-Lok, among others.