Knife locks, part 2

Knife Locks, part 2
 

The first part of this series dealt with the Back Lock, Liner Lock and Frame Lock. In this issue, we look at two ways of locking that are derived from these (the Compression Lock and the Nak-Lok), and at the Axis Lock and its variants.
 
Text and photos: Bas Martens
 
 
 
From top to bottom: Axis Lock, Bolt Lock and Compression Lock. Externally, the differences are barely visible.

It is not difficult to make a lock. If all the parts are big and heavy enough, you get something solid. But the trick is not just to make it strong, but also as small and light as possible. The secret lies in the distribution of forces, and that is exactly what happens with Spyderco's Compression Lock. This is related to the Liner Lock, and sometimes called a Liner Lock upside down, but it is much stronger.
The Compression Lock was developed at Spyderco by Sal Glesser, Peter Jhones and Vince Ford. It was patented in February 2001 and that same year the first knife with this lock appeared: the Spyderco C68G Gunting.
 
Some drawings of the US patent 6,553,672, applied for in 2001 and granted on 29 April 2003. Figure 3
shows the essence: the lock between the blade and the stop pin. (United States Patent Office)
 
The Spyderco Paramilitary 2 with the Compression Lock.

The essence of both the Compression Lock and the Liner Lock is a spring-loaded plate that blocks the blade. In order to close the knife, the plate must be pushed aside. But that is where similarities end.
The most striking external difference is that the Liner Lock is at the bottom of the handle, and the Compression Lock is at the top. In theory, this makes the Compression Lock easier to operate, as the mechanism is closer to the hand. This is mainly a matter of personal preference. But ease of operation was not the first thing the inventors had in mind; they wanted a lock that was as strong as possible. This has been done in a seemingly simple but very clever way.
The locking plate of the Compression Lock does not lie against the back of the blade tang, as with the Liner Lock, but on top of the back of the tang. Directly above the locking plate is the stop pin, a sturdy bushing that is placed transversely in the handle. When the blade is opened, the locking plate falls between the blade and the stop pin. A cam on the back of the blade spine rests against the front of the stop pin. Upward pressure on the blade (if, for instance, you apply a lot of force when cutting) is therefore absorbed by the stop pin. If you try to close the knife the back of the blade tang pushes against the underside of the locking plate, which in turn pushes against the stop pin. Finally, the liners in both handle halves lie across the top of the stop pin. In this way the forces are distributed among several parts of the knife.
 
   
Close-up of the Compression Lock. When the blade is open, the lock lies between the blade and the stop
pin. If the locking plate is pushed aside, the blade can be folded.

In order to close the blade, the plate must be pushed aside so that the blade can turn inwards. There must of course be room for this, but that is not a problem. The locking plate is part of the liner, and there is space for the liner on  the inside of the handle.
At first glance, the Compression Lock has some similarities with the Cold Steel Tri-Ad lock. It too uses the interplay of blade, stop pin and lock to distribute the forces on the blade. However, the Tri-Ad lock described in the previous issue is derived from the Back Lock and was developed several years after the Compression Lock.
Spyderco has been using the Compression Lock more and more in recent years. The 2016 catalogue featured three models with a Compression Lock; this year's catalogue has eighteen. One of these, the Smock, has a button on the left grip half, which pushes the lock plate aside. This 'button lock' has great similarities to the Nak-Lok.
 
Nak-Lok
The Nak-Lok is an idea of the Japanese engineer and knife maker Seiichi Nakamura, who patented it in 2006, and the American company Benchmade, that probably coined the name. Nakamura received his US patent 7,987,601 in August 2011. Benchmade had already released the first knife with a Nak-Lok three years earlier, in 2008: the Benchmade 480 Shoki, followed by the Megumi and Shori. All of these have been discontinued. The 2021 Benchmade catalogue no longer has any Nak-Lok knives.
 
The first drawing of Nakamura's US patent 7,987,601, issued on 2 August 2011. Number 17 is the button
that pushes aside the locking plate (2 and 26).
 
The Benchmade 480-1 Shoki (below) and 483 Shori, two Gentleman Folders with the Nak-Lok.

Still, the lock remains interesting. You can describe the Nak-Lok as a combination of a Liner Lock, Compression Lock and Back Lock. What it has in common with the first two is a spring-loaded plate that prevents the blade from closing. This plate locks into the back of the blade tang like a hook, just like the Back Lock. To close the knife, the plate must be pushed aside. This would be difficult, as the Nak-Lok lock is completely enclosed in the right side of the handle. Nakamura, however, had a simple solution: The plate has a pin on it, which protrudes from the left-hand side of the handle like a button. When the button is pressed, the plate is pushed aside and the blade can be folded. When the knife is folded, the button lies almost flush with the surface of the handle. Only when the knife is unfolded does it fully protrude.
 
The great advantage of the Nak-Lok is its elegance. There is no need for an opening or recess in the handles to operate a Back Lock or Liner Lock. The lock is completely enclosed. Only the button is visible, and that is not much bigger than the screw heads that connect the grips. On the Shoki, the button even has an identical appearance. It is therefore not surprising that the Nak-Lok has been applied to 'gentleman's knives': simple, graceful and stylish.
 
 
 
 
 
 

Close-up of the Nak-Lok on the Benchmade Shoki,
with the blade opened.
 
 
Axis Lock
To continue with Benchmade, we must look at the Axis Lock. This has been the backbone of the company for over twenty years. The vast majority of  all Benchmade folding knives have the Axis Lock, which was patented in 1998 by American custom knife makers William H. McHenry and Jason L. Williams. Its main feature is its ease of use.
As stated before, it is not at all difficult to lock the blade of a folding knife. You only have to make sure that the opened blade is blocked by a pawl, cam or axis. Yet it is much more difficult to ensure that this pawl, cam or axis can be easily operated to unlock the knife again. The release must be easily accessible, smooth and fast, but not too easy. Over the years, dozens of different designs have been invented for both locking and unlocking. The Axis Lock stands out because of its simplicity.
The story goes that McHenry and Williams worked on it for four years. On 12 July 1996, they applied for a patent for their 'Pocket knife with lock' and on 14 April 1998, the patent was granted in the United States, under number 5,737,841.
 
A drawing from U.S. Patent 5,737,841 by McHenry and Williams, for the original locking device with an axis
placed transversely to the blade. (United States Patent Office)

Apparently, McHenry and Williams were already negotiating with Benchmade at the time. In any case, the company bought the rights for the exclusive use of the lock, christening it the Axis Lock. In 1998, the same year the patent was granted, the first Benchmade knife with that lock was released: the 710, entirely designed by McHenry and Williams. The 710 became one of Benchmade's success stories and was made for almost twenty years with only minor changes, for example in the type of steel used.
 
The Benchmade 710 was the first Benchmade knife with an Axis Lock in 1998. The model
has recently been discontinued. (Benchmade)

The Axis Lock has become the main locking mechanism for Benchmade folding knives. The company has more than forty models with the Axis Lock or its derivatives Axis Automatic and Axis Dual-Action Automatic. In the latter two, the Axis Lock serves not only as a lock, but also plays a role in opening the knife. On the Axis Automatic, the blade opens mechanically when the lock is operated; on the Axis Dual-Action Automatic, the knife can be opened in the normal way, or automatically by pulling the lock all the way back.
Here, we limit ourselves to the Axis Lock. So how does it work? Pretty simple, like all good ideas. And like all simple things, it is not so easy to explain.
The heart of the mechanism is an axis, as the name implies. The axis lies perpendicular to the blade, in an elongated recess in the liners and handle scales. On the left and right, a button protrudes slightly from the handle, with which the axis can be moved. Attached to these buttons is an Omega spring, a wire spring so named because it resembles the Greek letter Omega (Ω). One end of the spring is attached to the axis, the other end is inserted into an opening in the liners. The construction is such that the spring is compressed when the axis is moved backwards – as can be seen in the photos. The springs ensure that the axis is always pushed forward. The space for the springs has been recessed on the inside of the handles.
 
    
 
When the blade is opened, the axis is in its forward position and the Omega spring is relaxed. When the knife is
closed, the blade pushes the axis backwards, and the spring is tensed.

The top and bottom of the blade also have recesses. At the bottom of the blade there is a slight hollowing into which the axis falls when the blade is closed. At the top the blade tang is flattened. When the knife is opened, the axis rests on this flattened part, securing the blade.
It is a beautiful construction. All the downward force on the blade pushes up the axis at the back. But that axis goes through the opening in the liners. To break through these would require an enormous amount of force. Unlocking, on the other hand, is a piece of cake. The Axis Lock only needs to be pulled back half a centimetre. This can be done with thumb and forefinger, but one of both is also sufficient. The blade can then be effortlessly closed.
 
   
The Axis Lock from above, with the axis in its forward position, on the back of the blade (right),
and with the axis in its rear position and the blade partly retracted (left).
 
 
On the outside, the Axis Lock is little more than a double-sided slider in the handle.

When the knife is closed, the axis, as mentioned, falls into a hollow area at the bottom of the blade tang. This is also useful, as the Axis Lock provides a little resistance. When opening the knife, the axis is pushed backwards against the pressure of the springs. It does not take much force, but at least the blade cannot fall open by accident. In addition, the Axis Lock is completely ambidextrous; it can be operated with equal ease by left and right handed users.
McHenry and Williams came up with a wonderful mechanism, and Benchmade did good business with the rights to the Axis Lock. Of course, since 1998, many variants have been invented, some outright copies, and other clever alternatives. Think, for example, of the SOG Arc Lock that will be discussed further on.
 
Hill Knives Top Lock
The Dutch knife maker Albert van den Heuvel (Hill Knives) has always been a great admirer of the Axis Lock, but was less enthusiastic about the lock release buttons in the sides of the handle. He developed an alternative, which he called the Top Lock. The two buttons have been replaced by a sliding bar on the grip spine. This is just as easy to operate, but is less disruptive to the lines of the handles. The knife shown is the Hill Knives Top Lock 01.

The Hill Knives Top Lock is mechanically identical to the Axis Lock, but is operated by a
sliding bar on the grip spine.

Ball Bearing Lock
In February 2002, Sal Glesser applied for a patent in the United States for his invention of a ‘Folding knife with a substantially spherical locking mechanism’. The patent was granted in June 2004, under number US 6,751,868. Meanwhile, the first Spyderco knives with the locking mechanism had already appeared, under the more practical name Ball Bearing Lock.
Depending on whom you ask, the Ball Bearing Lock is either a brilliant idea or simply a variation of the Benchmade Axis Lock. There is something to be said for both. In essence, the constructions have a lot in common: the vertical movement of the blade is stopped by a horizontally moving lock. The main difference is that the Benchmade Axis Lock uses a axis placed transversely in the handle, whereas Spyderco uses a ball, which is pushed forward by a coil spring.
 
The Manix 2 is one of the Spyderco models with the Ball Bearing Lock. The ball is not easily visible from
the outside, due to the plastic holder with its bevelled knobs.

The essence of the Ball Bearing Lock, as depicted in Sal Glesser's patent 6,751,868 of June 2004.

In their forward position, both block the movement of the opened blade. In order to close the knife, the ball and axis must be pulled backwards. With the Axis Lock, this is done by means of two buttons, which protrude from the left and right side of the handle. With the original Ball Bearing Lock, this was done by pulling back on the ball itself. This lock was therefore simpler and less sensitive to wear; the idea was that the freely moving ball would wear off evenly on all sides and would therefore have a longer life span.
However, the advantage of the Ball Bearing Lock was also one of its handicaps. The ball was relatively small, smooth and round, and therefore sometimes difficult to operate, especially with oil or grease. In some versions, such as the Spyderco Manix 2, the ball is therefore placed in a U-shaped plastic container, which protrudes from the handle with two bevelled knobs on the left and right. Thanks to these knobs, the Ball Bearing Lock is undeniably easier to operate, but they also hide the charm of the original design.
The Ball Bearing Lock is only used on two Spyderco models: the Manix 2 and P'Kal. This indicates that the original expectations, as a potential replacement for the Liner Lock or the Frame Lock, have not been met. It is difficult to say whether this is due to the construction of the lock, or its acceptance by the general public. The Ball Bearing Lock has, as far as we can tell, no serious defects. Nevertheless, it is easier to push a sheet of steel aside than to push a ball backwards under spring pressure. But Sal Glesser's patent is broadly formulated: the ball may be round, oval, flattened, cylindrical or a combination of these shapes. So perhaps we can still expect something.
 
     
Three positions of the blade and Ball Bearing Lock: blade opened, partially closed and fully closed.
 
The parts of the Ball Bearing Lock. Clockwise from the left: the blade, the right liner with the recess for the
right button of the lock, the steering piece of the lock in the back of the handle, and the lock itself, consisting
of a plastic holder with its side buttons, the spring and the ball.

Bolt Lock
The Bolt Lock is an invention of the American knife maker Walther Wells 'Blackie' Collins, also known for the assisted opening mechanism. It is best known for its use in the Spyderco Sage Series, which is dedicated to various locking mechanisms. The Bolt Lock consists of a spring-loaded steel bolt that wedges between a ramp on the back of the blade tang and the inside of the handle back strap.
When the blade is opened, the Bolt Action Lock mechanism automatically engages to lock it in the open position. Sliding the ambidextrous lock release buttons to the rear disengages the lock and allows the blade to pivot safely closed. In addition to locking the blade, the pressure from the Bolt Action Lock's steel bolt serves as both a detent and a self-closing mechanism to keep the blade closed.
Regrettably, we can only show the patent drawing. The Spyderco Sage proved very hard to take apart.
 

The drawings of Walther Collins’ U.S. Patent 4,451,982 for the Bolt Lock. (United States Patent Office)

SOG Arc Lock
We have not been able to find out when the SOG Arc Lock was first made. The accompanying drawings are from a 2005 patent application, but the lock probably dates from several years earlier. The Arc Lock combines elements of the Axis Lock, and the Bolt Lock.
The lock is provided by a bolt placed lengthways in the handle, with a raised, rounded head. The bolt is pushed forward under spring pressure and when the blade is opened, the head rests on the rear part of the blade tang and blocks its movement.
Roughly halfway up the bolt, there are two pins protruding to the sides. In front of these pins is a lever with a pivot point in the back of the handle, and two side knobs at the bottom, which protrude from openings in the handles. When the knobs are pulled back, the lever turns. It pushes the pins backwards, and with them the bolt, until the head of the bolt is released from the blade tang. The knife can then be closed. Since the lever is hinged, the buttons make an arc-like movement. This is how the Arc Lock got its name.
When the blade is closed, the head of the bolt lies against a ramp on the back of the blade tang. The spring provides sufficient pressure to keep the blade closed. When the blade is opened, it first pushes the bolt back, compressing the spring. Then the rounded part of the blade tang slides under the rounded head of the bolt and the blade can be opened completely.
Item 190 on the patent drawings is a safety catch, which, when the blade is closed, can be turned upwards into a recess of the bolt. It is thus blocked and the blade cannot be opened.
The Arc Lock has disappeared from the SOG range. It has been replaced in 2018 or 2019 by the XR Lock, a copy of Benchmade's Axis Lock.

The SOG Arcitech with an Arc Lock. This lock mechanism has disappeared from the SOG catalogue.
 
 

These drawings are from a 2005 patent application, which covers a wide variety of locking mechanisms,
including the Arc Lock. (United States Patent Office)