Manufacturing a folding knife : What do I need ? 24 December 2019

Manufacturing a folding knife : What do I need ?

Manufacturing a folding knife : parts to be prepared and materials to be chosen

Which steel do we use to make a folding knife ?

Whether you’re a beginner or an expert, this question inevitably arises before making a folding knife.

What composes a folding knife ?

The answer to this question can be both simple for a basic knife and complicated for high-class knives, which are state-of-the-art technology.

Thus, a basic folding knife will consist of :

- A blade
- A spring
- Two plates
- Two scales for the handle
- Rivets, nails or screws

Reading this could make you think : “Couldn't be simpler than that.”

Yet, a proper knife could not be made with so much simplicity. To be crafted, it will need all the know-how of the knife maker… Which consists, to a large extent, of choosing the most suitable steels and materials for the preparation of the scales and decoration elements.

Plates, screws, rivets, struts, ball-bearings, slabs made from various materials for the manufacture of scales and decorative parts,   Eurotechni offers a wide choice of knife making steels and materials for the manufacture of your knives, and our consultants will be able to guide you according to your own criteria.

The main element : the blade

The main qualities sought for a blade are sharpness, cutting performance, resistance to deformation and in some cases, corrosion resistance.

The choice of the steel used will be made according to the purpose of the knife and its use, following a compromise whereby the knife maker will take several factors into account, some of which will be the equipment and tools available to him to work the material.

The first of these choices will concern the type of steel : Carbon or stainless steel ?

All steels are made from the alloy of iron ore with carbon, whose proportions are generally between 0.02 and 2%.

In fact, if there is more than 2% of carbon in the alloy, the latter becomes cast iron, which is not suitable for knife making. However, there are exceptions, for example carbon steels made from powder metallurgy, such as the excellent Vanadis 8 SuperClean tool steel from our partner Uddeholm Voestalpine (2.3% carbon knife making steel).

Choosing carbon steel :

Carbon steel is appreciated for its ease of use and hardness after hardening but its vulnerability remains corrosion resistance.

Some knife makers will only swear by carbon steel, because of, among other good reasons, the quality of the cutting edges obtained, its cutting properties and the patina, taken over time by the blade, which tells a bit about the history of the knife.

This choice is off course accompanied by particular, but rarely unescapable, constraints. Although meticulous maintenance remains necessary, some of these steels such as 80CrV2 or 90MnCrV8 will be particularly appreciated in the manufacture of outdoor, utility and off-road knives.

No less than twenty grades of carbon steels are available from Eurotechni, in a wide range of packaging and formats.

With round bars from 12 to 20 mm in diameter (100c6 and XC50), flat bars from 4 to 10 mm thickness (DNH7 - XC75) for forging, or bars whose thickness has been optimised for the use of a stock removal knife (XC75, XC100, 135Cr3, C130, etc.), all desires become possible for the experienced as well as the beginner.

Choosing stainless steel :

The choice of this type of steel will be dictated by the prupose of the knife. The knife maker will be seduced by the cutting abilites of stainless steel and its ease of maintenance, thanks to its anti-corrosion properties (Z40, Z50, 12C27, etc.).

The best steelmakers, such as Böhler, Uddeholm Voestalpine, Sandvik or Damasteel, compete in creativity and ingenuity, using the most modern technologies to produce ever more efficient special steel alloys.

The hardest thing will be to make your choice !

As with any steel, the knife maker will have to make a compromise between blade hardness, edge retention and corrosion resistance. The latter is obtained by a quantity of chromium present in the alloy (between 13% and 30%).

Eurotechni offers a wide range of stainless steel grades for knife making  in packaging and dimensions adapted to your way of working. Even if stainless steel can be forged, it is way more widely used in stock removal (12C27M, 14C28N, X90CrMoV18, Niolox, etc.).

Just like carbon steel, stainless steel must undergo a precise heat treatment adapted to the type of knife manufactured, in order to benefit from all its qualities. However, for this type of steel, it must be possible to reach quite high temperatures (1020°C minimum) precisely and for several minutes. To do this, the blades must be treated in an electric oven, in an environment protected from the ambient air, using for example stainless steel strip or protective paint such as Condursal Z1100.

If you do not have the necessary equipment for this crucial and delicate operation, do not hesitate to contact our teams. Eurotechni will be able to carry out for you, by the book, the heat treatment of your pieces.

-> European and french regulations stipulate, for materials intended to come into contact with food products (MCDA), steels used for knives in particular, a minimum chromium content of 13% in France (Order of 13 January 1976) and 12% in the rest of Europe to be certified as food grade. Although this directive applies to the manufacture and marketing of knives and cutlery, it does not, however, concern folding knives.

Each Eurotechni data sheet mentions the food or non-food quality of the selected stainless steel.

Why not a bit of both ?

In addition to traditional carbon or stainless steels, Eurotechni offers a wide selection of steels made from the most modern technologies (Nitrobe 77, RWL34 or M390 produced by powder metallurgy) or more traditional steels such as damascus steels (DX93X, DSC) and special steels (sandwich steels 90MV8/XC10, NCV60/304L, VG10 San-maï).

All these steels find their place in the manufacture of folding knives.

A spring to lock the blade.

The spring is often one of the most forgotten parts of a folding knife. The blade is often evoked, having to be solid, sharp and resistant. We talk about handle ergonomics, its practical or aesthetic aspect. But little is said about the spring, except that it is too hard, or too soft, or even worn out.

However, it is an essential element of the knife which should not be neglected in its shape, in the choice of its material. And above all, one should take special care in its heat treatment.

The role of the spring in a folding knife :

The spring has to make it easier to open and close the blade safely, while maintaining it in any position.

Not all folding knives have a spring to hold the blade. The Capucin, with its simple, antique design, requires only 2 nails while the Piedmontese has a friction system completed by the position of the user's thumb on part of the heel of the blade. As for the Nontron and the famous Opinel, it is a rotating ferrule which ensures the locking of the blade.

For all the other folding knives, we should speak of "springs" in plural because the shapes can be as diverse as the locking systems.

Possible types of springs :

The best known are the flat or forced notches ("slip-joints" for our American friends): The spring is housed in the top of the handle between two plates and rests on the heel of the blade to keep it open or closed.

The pump knife or "lock-back" is a locking system where the spring releases a locking rod from the heel of the blade.

The "liner-lock" uses one of the plates cut and worked to play the role of the spring. In the same vein, the "frame-lock" uses a part of the handle, necessarily metallic, to fulfil the same function as the liner-lock plate. These systems are known as "plate-lock" systems.

More confidential, the "Axis-lock" mechanism, developed by the American knife manufacturer Benchmade, is equipped with a spring, but it does not support the force exerted on the blade, which is held in place by a movable pin and a stop that blocks the blade at its heel.

The "palm" knife, on the other hand, is equipped with an external spring since it is placed on the outside of the handle and envelops it. It is equipped with a ring that unlocks the blade whose heel is hooked in the open position.

The list of locking systems could be infinite, because of how fertile the imagination of the craftsmen is.

Steels for springs :

Eurotechni has selected the best steels for the manufacture of springs, whether classic, liner-lock or palm type and even pump or axis-lock type: X20Cr13 for stainless steel and XC45, 45Si7 and 56Si7 for carbon steel.

Why heat-treating your spring is necessary :

The heat treatment of springs is particularly important to obtain perfect parts whose flexibility and strength are balanced and durable over time.

Eurotechni can carry out this task for you with the most efficient equipment. Do not hesitate to contact our teams for more information.

The plates: a case for the blade and the spring.

The plates : spine of the knife :

Plates constitute the "skeleton" maintaining the structure of the knife, and preventing  any contact of the moving parts (blade and spring) with the most fragile materials of the handle (bolsters, ribs) thus avoiding premature wear. In "liner-lock" type systems, one of the two plates replaces the classic spring and allows the blade to be opened and closed with one hand.

An aesthetic asset :

They are also an interesting decorative element because they are easy to work with. They can be sculpted alongside with the spring in an overall pattern for an additional aesthetic  advantage to the knife .

Steel for plates : Z8C17 or non-ferrous metals :

Eurotechni has selected for you the Z8C17 stainless steel (or X6Cr17 AFNOR standard) for the plates manufacture. This ferritic stainless steel is non-hardening and perfectly resists to corrosion without treatment. However, the use of Z8C17 is not recommended for the manufacture of "liner lock" type knife plates where conventional spring steel is preferred.

The plates can also be made of non-ferrous materials such as brass, titanium or nickel silver.

Z8C17 stainless steel as well as the non-ferrous metals recommended by Eurotechni for the manufacture of folding knife plates can also be used for the manufacture of bolsters, guards, false parts or appearance parts and, why not, handles.

Two scales for the handle :

Many factors to be considered :

Knife handle, whether folding or with a fixed blade, must meet a certain number of criteria (not exhaustive) that the craftsman will classify in order of priority, according to the end use intended for the knife:

- Ergonomics,

- Solidity,

- Sustainability,

- Aesthetic.

A multitude of materials can be used with certain considerations, more abstract but no less important at a time when they had been somewhat neglected or even forgotten: respect for the environment, compliance with regulations, ethical and moral considerations.

Natural origin materials proposed by Eurotechni respect these requirements (stabilised beech wood).

Utility of new materials :

Constantly searching for adapted, performing and original materials, both aesthetic and innovative, Eurotechni offers inserts made of acrylic resin with inclusions or in braided or unbraided carbon fiber (Fat Carbon).

These new materials, with surprising aesthetic qualities, are the result of the creativity of passionate craftsmen, who carefully combine colours and materials.

The result is up to the expectations : plates that are easy to work and shape, a longevity that is close to unalterable and a design that is often breathtaking.

The most modern materials, created for the aeronautics industry, and long used in cutting-edge technologies for their reliability, resistance and light weight are now available to the world of knives.

Rivets, nails and screws.

An indispensable part of the folding knife:

In the world of folding knives, nothing could be done without rivets, nails or screws. Of course, chemistry has made it possible to create permanent adhesives that allow reliable and solid assemblies, but even if these adhesives are very well suited to fixed-blade knives, they will not be suitable for a folding knife : The rule of mobility prevails.

In order to ensure that each moving part of a knife works properly, it is best to use the good old recipes : nails, rivets or even screws, which have appeared more recently in assembly workshops.

Anatomy of rivets, nails and screws in knives manufacture :

Nails are cylindrical wires made of steel, stainless steel or brass that the assembler will have to cut to size and hammer with dexterity on each side of the handle to obtain a slight bulge and boss that will hold all the pieces of the knife together.

The rivets will be of a specific length, have a flat or domed head and are assembled in male/female pairs.

The major disadvantage of this type of assembly is ... its ease of disassembly and therefore the risk of damage to the knife.

The manufacture of a folding knife therefore requires little recipes and supplies. But one must not forget two important components, immaterial, yet essential :  Imagination, and motivation.

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