In the article Knives: The Evolution of Steel, we examined the modern materials used to make the blades of modern knives.
Knives can be divided into two broad categories - with a fixed blade or "fixed" and folding knives or "folder".
For most of human history, "fixes" were unconditionally in the lead, but in our time their spread has significantly decreased - often people around them even negatively perceive folding knives, what can we say about the "fix" hanging on the belt? And from a practical point of view, most people do not have any special need for a knife with a fixed blade - most often they are worn outside the city by tourists, hunters and other similar categories of users. However, in this segment, folding knives are becoming more widespread. Therefore, in this article, we will talk about folding knives.
Despite the predominance of "fixes", the first folding knives appeared before our era. The first samples were found on the territory of modern Austria with an estimated creation date of about 500 BC. And the folding knives produced during the Roman Empire, due to the originality of the applied design solutions, could give odds to the products that appeared a couple of thousand years later.
In the future, knives have gradually evolved, acquiring a look more and more similar to that used in modern products.
With the development of the technical and technological skills of mankind, the design of the knife has undergone significant changes. However, design changes were not always dictated by technology - since ancient times, a person has been distinguished by the ability to complicate life for himself and his loved ones, therefore, the parameters of knives are significantly influenced by legislative restrictions in different countries. In Russia, in terms of knives, there is one of the most liberal laws in the world - this issue was discussed in detail in the article Knives in Russia: edged weapons or not ?. We will return to the topic of the negative impact of lawmaking in different countries on the design and characteristics of knives in subsequent materials.
From a technical point of view, a folding knife is much more difficult than a fixed blade knife. Of course, a lot depends on the user's pickiness - someone still uses knives of the Soviet period and does not feel any discomfort at the same time, but knives of this level of performance cannot be attributed to high-tech products, and their production can be established in any artel. On the other hand, you quickly get used to good things, and if you use modern products made with the latest achievements of the knife industry for at least a short time, you somehow don't want to "go back".
If in the previous material we said that starting from the middle of the 20th century, stainless steel knife steels, in principle, have sufficient characteristics for comfortable practical use of the knife, then a significant part of the design solutions that ensure the comfortable and safe use of folding knives appeared somewhat later, towards the end XX century.
Lock tightly
No matter how trite it sounds, the main difference between a folding knife and a fixed one is that in the first the blade folds. Accordingly, for a comfortable and safe use of a folding knife, it is necessary to ensure that the blade is fixed both in the closed position (so that it does not open in the pocket) and in the open position (so as not to chop off the fingers during use).
For a long time, special attention was not paid to this problem - the blade was, in fact, fixed only by the friction force. A little later, a spring-loaded rocker appeared, which opens with increased pressure on the blade - the predecessor of the Back Lock.
Modern knife locks have really effectively begun to block the blade, which must be opened by a separate push or movement of special structural elements, and not just by pressure on the blade.
There are a great variety of locks - the aforementioned Back Lock, Liner Lock and its varieties Frame Lock and Compression Lock, Axis Lock and its varieties, Blade Lock, Slide Lock, Viroblock and many others. The most popular are Back Lock, Liner Lock, Axis Lock and their varieties.
The Liner Lock is a bent part of the inner side plate of the knife, which abuts against the heel of the blade when open. To prevent the knife from opening when folded, a metal or ceramic ball is integrated into the die, which, when closed, enters a special recess in the blade.
The Compression Lock is similar in principle to the Liner Lock, but the locking plate is accessed from the back of the knife handle.
The most reliable lock from the Liner Lock family can be considered the Frame Lock, since in it the locking unit is a part of the handle itself, usually made of titanium or steel, which is much thicker than the liner in the Liner Lock. The locking plate can be either part of the handle itself, or a separate element attached to the handle with screws. When making a Frame Lock from titanium, it is most often additionally equipped with a steel cracker in the front part in order to prevent the titanium plate from sticking to the blade steel. The additional reliability of the Frame Lock is given by the fact that it is wrapped around the fingers of the hand during operation, and this additionally contributes to the fixation of the lock.
Knife locks Axis Lock and Arc Lock, which are locked by a spring-loaded pin, are considered quite reliable and easy to use.
It would seem that everything that is possible has already been invented in the field of knife locks. However, more and more new designs appear. For example, one of the oldest knife locks is Back Lock. Its disadvantages include the fact that work hardening gradually forms during operation, as a result of which a vertical backlash of the blade appears and the reliability of its fixation decreases.
Based on the Back Lock, American knife designer Andrew Demko developed the Tri-Ad Lock for Cold Steel in 2008. If in the Back Lock the power loads fall directly on the rocker arm of the lock, then in the Tri-Ad Lock the force during power work falls on the fixed transverse axis, and the rocker arm of the lock wedges the heel of the blade and the same axis from the reverse side. At the same time, the hole for fastening the rocker arm is made oval, that is, the rocker arm of the lock has a small play, which allows it to independently choose the gap when forming work hardening, excluding or minimizing the occurrence of blade play. This makes the Tri-Ad Lock one of the most reliable knife locks around.
There is no doubt that engineers and designers will not stop there, and other designs of knife locks will be developed in the future.
For a comfortable and safe use of a folding knife, it is necessary to ensure that it is easy to open and close. This is ensured by the design of the axle assembly and the devices for extracting the blade.
Axial node
In old folding knives, the axle assembly was simply the axle on which the blade was mounted. Poor workmanship led to the fact that the knife opened with a creak and crunch, with an uneven force.
Then, washers made of non-ferrous metals were additionally installed on the axle, which, having less friction, ensured a smoother extraction of the blade. With high-quality polishing of a washer made of alloys of brass and bronze alloys, it is possible to achieve the highest smoothness of the blade opening. To reduce friction, sometimes the washers are made perforated (however, according to the author, the perforation is only clogged with dirt).
An even smoother opening is provided by fluoroplastic washers. However, they are less resistant to power loads - with strong side loads, PTFE washers can be crushed. In addition, often knives with fluoroplastic washers have a small lateral blade play. Some companies, like Cold Steel, combine metal and PTFE washers.
The most modern solution is the use of bearings in the axle assembly. Bearings can be open and closed, with metal and ceramic, ball and roller rolling elements.
The knives with axle bearings open incredibly quickly and smoothly. However, everything has a price. Even if we do not talk about the increase in the cost of the knife, the bearings are more prone to contamination, after which they become less smooth. Bearings with steel balls and rollers can also corrode.
If the bearing elements are made of ceramics, then they are not only absolutely resistant to corrosion, but also literally grind the debris that gets into them, for example, dirt and sand, and are easily washed out with water.
In general, from a practical point of view, we can say this - for power work and use in nature, metal washers are preferable. For using a knife in a city with light loads, fluoroplastic are also quite suitable.
Bearings are more likely a "luxury", there is no objective need for their use on folding knives. On the other hand, user requests contribute to the proliferation of bearings in folding knives, an increase in the number of bearings sold contributes to a decrease in their cost, which in turn contributes to their distribution in all types of folding knives, and then the cycle repeats.
One-handed opening
One of the most important factors determining the usability of folding knives is the ability to conveniently open (and close) them with one hand.
On old knives, such an opportunity was often not provided; there was only a small recess on the knife blade, behind which the knife could be opened with the second hand.
It is convenient to open with one hand automatic knives with a blade that opens under the action of a spring - all you need to do is press a button or move a small lever. However, the turnover of such knives is often limited, and their design is further complicated, which makes them less reliable.
The simplest devices for one-handed opening are holes and pins on the blades of knives. For example, Spyderco patented a round hole that has become an integral design element of the company's knives. Many companies use protruding pins on the blades. Both solutions have both advantages and disadvantages, and therefore their supporters and opponents. A large hole in the blade weakens it, but does not interfere with cutting. In turn, the pin requires a smaller hole that almost does not weaken the blade, or it can be made in the form of a platform on the butt of the blade, but the pin "eats" part of the useful length of the blade.
The American knife designer Ernest Emerson developed the so-called "Emerson's hook" - a hook in the upper part of the blade, which allows it to automatically open when removed from the pocket due to the hook on the edge of the pocket. Someone likes this solution (including the author), someone considers it unsafe (and will also be right), one thing can be said for sure - Emerson's hook pulls the pocket of his trousers mercilessly.
Combined solutions have also appeared - the combination of the Emerson hook and the peg-platform, which are also quite comfortable, but fairly tearing the fabric of the pocket when used.
The emergence of axial nodes that ensure the opening of the knife with minimal effort led to the emergence of another type of opening method - due to the so-called "flipper" - a protrusion at the base of the blade protruding from the knife handle when folded. This is where the concept of "flipping" came from, that is, to throw a knife abruptly, combining pressing on the flipper with an inertial movement of the hand. On knives with polished washers or bearings, light pressure on the fin is enough to fully open the knife, without additional hand movement.
The methods of quickly opening knives are not limited to this, but they are much less common. It is also worth mentioning that some locks, for example, Axis Lock and Arc Lock, allow you to open and close the knife, combining the opening of the lock and the inertial opening by hand. Also, often on knives, several methods of opening are combined, for example, a pin and a fin.
Ease of wearing
Folding knives have been called "pocket knives" because they can be carried in a pocket without a scabbard without fear of cutting. However, this is not always convenient. The introduction of a clip made it possible to radically increase the convenience of carrying folding knives. The clip first appeared in 1981 on Spyderco's Worker knife. From that moment on, folding knives began to be carried not “in the pocket”, but “on the pocket”.
For all its seeming simplicity, this element is very important - the clip should make it easy to put on the knife "on the pocket", but hold it firmly, to tear the pocket tissue to a minimum when putting on and removing the knife, not to dig into the user's hand when working with the knife.
Ideally, the clip should be able to be rearranged for left-handers and right-handers, as well as to allow the knife to be carried up or down at the user's choice.
There are deep-set clips, when the presence of a knife "on the pocket" is almost invisible.
Automatic knives, balisongs, multitools and other types of folding knives, blade coverings and handle materials are beyond the scope of this article. Perhaps we will return to them in subsequent materials.
Finally, I propose to watch a video of assembling and disassembling the IFS-20 knife, in the design of which there is not a single screw.
