Knife manufacturing is the process of producing a knife using one or more of the following methods: stock removal, forging to shape, welded lamination, or investment casting. Typical metals include carbon steel, tool steel, and stainless steel. Bronze, copper, brass, iron, obsidian, and flint have all been used to make primitive knives.
It takes many steps to make a knife, and most people don’t realize how complicated the process is. This article will explain in great detail how knives are made.
Knife Making Process
There are four main steps to making a knife, and each one has more steps that are important for making a high-quality kitchen knife. Here’s what they are.
- Forging is the process of heating metal and hammering, rolling, or pressing it into the shape of a blade.
- Grinding is the process of smoothing the edge of the blade to get rid of the burr and finish it.
- Heating the steel: Heating the steel makes it harder and helps it keep its cutting edge longer.
- Finishing: Putting the finishing touches on a knife, like putting on the handle and sharpening and polishing the blade.
Difference Between Modern Knife-making and Traditional Knife-making Process
Before we talk about how kitchen knives are made, we need to make one important point clear. This article will talk about how forged knives, or traditional knives, are made. Some modern knife makers use stamped knives to make a lot of knives because it’s easier to cut a blade out of a large sheet of steel than to hammer a steel block over and over again.
Even though the differences are clear, some modern tools are used in traditional knifemaking to make things easier. Power hammers are used to speed up the shaping process. Without them, the steel block would have to be hammered and heated up many times before it could be shaped into a blade. Also, instead of sandpaper, machines with belts are used to smooth the blade after it has been forged.
Here’s a detailed look at each step in the process of making a kitchen knife.
Part 1: Forging
The first step in making a knife is to forge the blade. This is the process of heating the materials to a certain temperature so that they can be formed into a blade.
Steel is used most often and may be the best material for making knives. Steel needs to be cut, no matter if it is high-carbon steel or stainless steel.
Cutting Steel
You need a thick, small piece of steel that is long enough to make the blade you want. Steel can be cut in many different ways. A metal chop saw is the most common tool used to make knives by hand. The shape of a block of steel doesn’t matter because it will be forged into a blade. Other ways to cut steel include laser cutting, waterjet cutting, and oxy-fuel cutting, to name a few. However, these methods aren’t used much for making knives and are mostly used in other areas.
How to Choose the Steel
There are so many different kinds of steel that there is no one best steel for kitchen knives. Different kinds of steel will make different things that some people will like and others will not. For most people who don’t cook often, the type of steel doesn’t matter as much as how to take care of it.
Most kitchen knives are made of stainless steel because it doesn’t rust. Stainless steel can be made of either standard steel or carbon steel. Still, there are other kinds of steel, like Damascus steel, tool steel, and alloy steel, and each of these has its own qualities. No matter what kind of steel is being used, the process is the same, with only minor changes to how it is heated.
Heating Steel
In the forge, the steel block is heated up to about 1,100 C/2,000 F. Different steels have different temperature requirements. Steel is heated until it turns the right color because it’s hard to tell exactly what temperature it is. This can be any color between yellow and cherry red. As long as it’s soft enough to start shaping with a hammer, it’s good enough.
Some Japanese knife makers cover the steel with wet paper and straw ash to keep it from getting too hot. This method, called “ash coating,” makes up for the carbon loss caused by heat. It is mostly used by knifemakers who follow ancient methods.
Hammering
When the steel is in the right shape, it is put on the anvil so that the hammering can begin. The steel is pounded to squeeze the steel molecules together. As a result, the steel starts to take shape. Blacksmiths hit the steel with the hammer many times and then turn the piece 180 degrees to work on the other side.
As the steel cools during hammering, it becomes more difficult to compress its molecules and achieve the desired form. Therefore, it is heated once more on the forge to facilitate this procedure. This is done again and again, depending on the type of steel and the blacksmith’s preferences.
Some blacksmiths fold the steel as they hammer it to get rid of imperfections and make the metal stronger as a whole. Most of the time, this is done to carbon steels so that the carbon content is spread out evenly in the block.
Shaping and Quenching
When you hammer the steel, you squeeze its molecules together and make it harder. You also shape the steel into a blade. As the hot steel is hammered by the blacksmith, it changes into the shape that was wanted. This doesn’t happen right away, of course. It takes a long time and a lot of hammering.
During the shaping process, some blacksmiths cool the steel by putting it in an industrial quenching oil or water. Quenching is the process of cooling the steel block right after hammering to squeeze the molecules together even more. We’ll talk more about it in the section below about heat treating.
Quenching is a type of heat treatment that is done both before and after forging. The process of making a knife is a never-ending cycle of heating, hammering, and cooling the steel until it is just right before the next step, which is grinding.
Part 2: Grinding
After the blade has been forged into the desired shape, the following stage is grinding. The knife might be ground for a variety of purposes. You may think of it as a way to both thin out the blade and give it a more refined feel. Once the forging process is complete, the blade is often thicker than you’d see on a kitchen knife.
Multiple belts of varying grits can be seen on grinding machines. The grits used in the grinding process can range from 200 to 2,000. Grinding the knife is done in the same way whether the blacksmith does it or someone else does it.
Smoothing the Blade
The forge residue is ground away from the blade while it is kept against the machine’s belt while it is in operation. Grinding the entire blade and smoothing out certain areas like where the handle will be connected and the bolster, if the knife has any, will prepare it for thinning.
Due to the fast rotational speed of the grinding machine and the metal removal action of the belt, the blade heats up extremely rapidly. The blade will be ruined if you keep it up against the belt grinder for too long.
It is essential to periodically cool the blade so that you don’t have to start over from the beginning. After the steel has reached the desired temperature, it is cooled by being submerged in a bucket of water. After being heated during the forging process, the metal is cooled several times before being prepared to go back into the grinding machine.
Thinning Down
The blade needs to be thinned down once it is smooth enough to use. After forging, a kitchen knife’s blade will always be thicker than expected. For this reason, it must be reduced in thickness, but a grinding belt won’t do the trick.
A flat-bed grinder is used to thin down the blade instead of a grinding belt, which would only expose a tiny portion of the blade at once. Since it’s simpler and results in thinner steel all throughout the blade, it’s the method of choice.
In the case of some blacksmiths, the blade is polished before being thinned. The main purpose of this is to get a feel for how the final product might look. Like the rest of the steps in producing a kitchen knife, this one is optional because it comes down to personal taste.
When the blade is finished being ground, it is typically half as thin as it was before. The grinding machine can leave scratch marks on metal due to the grit of the belt reducing the metal’s thickness. Any remaining scratches that you wouldn’t want to see in a brand new kitchen knife can be removed with one last grinding on a high-grit belt.
Different Types of Grinding Machines
When grinding anything, a variety of machines with varying belt grits are employed. We can’t use the same grit to sharpen the entire blade of a kitchen knife, thus this is the result. If that were the case, it would really be detrimental to the knife. This is why a variety of grinding wheels and belts are used to achieve optimal results and create a high-quality blade.
The next process can begin once the blade has been ground to perfection.
Part 3: Heat Treating
Knife steel must be heat treated to increase its hardness before the finished product can be used. Similar to the other described aspects of knife production, the process of hardening the steel involves a number of phases.
For the steel to be flexible enough and long-lasting in its intended usage, it must be hardened so that it can retain its cutting edge.
A normal-feeling knife might result from skipping heat treatment, but it would have trouble performing its designated function—cutting materials. All metals require heat treatment to get the desired level of hardness and edge retention.
Normalizing
When molecules are compressed, as they are during forging, they grow in size. There are a number of issues with this, the most significant being that it will lessen the blade’s hardness and make it less capable of maintaining a sharp cutting edge. Because of this, heat treatment is essential, and the first step is to normalize the steel by heating it.
The blade is returned to the forge and is heated more evenly and cautiously by being rotated regularly. Warping and cracking might occur if one side is heated more than the other. The steel does not have to reach forging temperatures because it is back in the forge to undergo heat treatment rather than being hammered into shape. Instead, it is heated to around 800 C/1,500 F, just below the temperatures required for hammering.
Quenching
The steel is hardened by quenching so that it does not soften during the rapid cooling that follows. Phase transitions at lower temperatures will not have enough time to occur in the steel. The steel can be quickly cooled below the temperature at which it begins to harden—around 480 C/900 F—by placing it in a bucket of oil or water.
Quenching is a simple scientific concept. Without the last step of heat treating, blacksmiths who have finished the handle assembly and are ready to ship out to their customers would provide a blade that is not as strong as promised. Inadequate metal is created from phase transitions that occur during cooling when the blade cools slowly from high to low temperatures. This can cause crystallites to develop, which weaken the blade and is therefore undesirable.
Quenching Process
The blade is heated in the forge to the proper temperature and then cooled by submerging it in a pail of oil or water. This is where it will remain until it reaches the desired temperature. Fast cooling from high to low temperatures makes the steel stronger than previously.
While oil is typically used for this purpose, water is also a viable option. The knife is ground to the proper shape, then heated in a forge, and finally quenched in oil. Because water cools steel far faster than oil does, using water as a quenching medium can cause cracks and warping in certain steels if the steel is not specifically designed to withstand such rapid cooling. What follows is a quick examination of the differences between the two.
Water Quenching vs. Oil Quenching
The rate at which the hot steel is cooled is the primary distinction between oil and water quenching. When opposed to oil, water has a much faster cooling effect when used to submerge a hot steel object. This creates a harder steel, which might be desirable depending on the steel, but it also creates a more strained component that is more likely to chip or break than less hard steel.
Carbon steel also requires rapid cooling after being heated. The faster the steel cools to trap the carbon atoms, the lower its carbon content. Quenching in water achieves the desired effect for low-carbon steel because it cools more rapidly, but higher-carbon steel requires more effort and time.
It all boils down to the fact that neither is a clear winner. As with many of the preceding processes, this one depends on the steel used and the personal tastes of the blacksmith.
Air Quenching
Rapid cooling can cause damage to certain steels. Some types of steel benefit from the aforementioned phase transitions, making them harder to break. These steels are allowed to gradually cool at room temperature.
Other Heat-treating Methods
Annealing
While it is typically necessary to harden steel in order to create a premium kitchen blade, the inverse is sometimes the case. Metals that are overly hard might chip or break easily, especially if they come into contact with other hard objects in the kitchen like cutting boards or pots and pans.
The hardness of metal can be reduced with the aid of annealing. Annealing is similar to quenching in that the metal is heated, but the temperature is maintained just below the melting point. To avoid this, modern metalworking skips the forge in favor of big, specially designed ovens with plenty of ventilation. The metal is kept at this temperature for a predetermined duration before being gradually cooled.
This process softens the metal, making it suitable for subsequent cold processing. Metals are more prone to cracking or even breaking apart when they are cold and bent. Ultimately, annealing results in a softer metal, which is more malleable because of its increased flexibility. Since there is no cold labor involved in making a kitchen knife, annealing isn’t typically required unless the type of steel being used specifically calls for it.
Tempering
It is possible to soften metal by tempering it. Tempering, like annealing, weakens the material, although not as dramatically as annealing does. When steel is hardened beyond what is necessary, tempering can reduce the amount of unneeded hardening while maintaining the steel’s overall hardness.
When hardening metal, it is common practice to increase the temperature of the metal in a vacuum, air, or inert atmosphere to get it up to the desired hardness. In order to soften a metal, it must be heated to a high temperature, which in turn increases its hardness.
In the same way that annealing does, this process entails maintaining the metal at the desired temperature for an allotted amount of time before allowing it to cool naturally. Typically, for every inch of thickness, the metal is held at the designated temperature for an hour.
The process of producing knives does not involve either of these heat treatments. Because a harder metal maintains an edge for longer, quenching is the most frequently required heat treatment procedure.
Part 4: Final Touches
The blade is nearly complete after it has been quenched to increase its hardness. Now that the blade is complete, the blacksmith may start working on the handle.
Installing the Knife Handle
Japanese handles, sometimes known as wa-handles, and western handles are the two most frequent forms of knife grips. The knife’s tang, or the section that extends into the handle, must be attached reliably.
The handle is typically fastened in place with epoxy glue and pins. Both ends of the tang are used to join the two halves of the handle, which is then secured with glue. The handle is then fastened in place using pins that enter the tang. In order to attach the handle to the blade, tiny holes are drilled in the blade during the manufacturing process.
The wa-handles are integral, meaning there are no pins holding them together. Therefore, Japanese knives have a unique method of attaching their handles. To attach the tang to the handle, it is heated up and pushed in rather than utilizing pins. The resin is released as the wood is burned with a searing tang. The handle is securely fastened in place by this adhesive substance. When attaching a wa-handle to a blade, the wood may crack. One of the reasons wa-handles are more expensive than western handles is that making them is a specialized task.
Polishing
There are unsightly markings left on the blade after quenching. Having identified them, the blade is returned to the grinder for another round, this time with the intention of removing the aforementioned imperfections and restoring the metal’s original sheen. Typically, a coarse grinding wheel is used to polish the blade, and then, if necessary, metal polish is applied.
Sharpening
Manufacturers ensure a razor-sharp edge since they know how crucial a good first impression is. After the blade has been given the appropriate aesthetic finish, it is sharpened using a whetstone and water. Paper is used as a test of the newly sharpened blade. If a kitchen knife can easily cut paper, it’s sharp enough for use and ready to be packaged.
DIY knife sharpening using honing steel will have your blades performing like they did when you first got them.
Japanese Knife Forging Techniques
Many Japanese knives are forged utilizing alternative methods that give them their own distinctive characteristics. These subtle improvements enhance the knife as a whole.
San Mai
The San Mai method of forging is used to create several Japanese blades. The carbon steel in this style of blade manufacturing is placed between two thinner layers of softer steel. Simply said, this is done so that both types of steel can perform at their highest levels. Although carbon steel is tough and keeps its edge well, it is also fragile and can be chipped if care is not taken.
This is why Japanese chefs are so careful when using their knives; not only do they want to produce clean cuts, but they also want to keep the knives in good condition for future use. On the other hand, softer steel can better absorb shocks and take hits without breaking. By sandwiching carbon steel between two layers of softer steel, San Mai creates a kitchen knife blade with the exceptional edge retention and wear resistance.
The carbon steel in the center is revealed when you remove metal off the edge of a San Mai knife because Japanese blades are single-beveled. In Japan, this is a well-known method of forging. Some other examples of Japanese forging methods are provided below.
Kobuse
Kobuse is like San Mai except with the roles reversed. The carbon steel core is softer than the outer layer, and the outside layer is harder steel.
Honsanmai
Even while Honsanmai, like Kobuse, is made of softer steel in the center and harder steel on the exterior, it differs in that the hard steel on the outside has an additional layer of coating. Kawagane, a high-carbon variety of Japanese steel, is typically found on the surface.
Maru
The traditional method of forging blades from a single type of steel, often high-carbon steel, is called Maru, sometimes known as muku. The term “maru” refers to the type of high-carbon steel used to make the vast majority of Japanese knives and swords.
These are only some of the many techniques utilized by Japanese blacksmiths in their work. Many more forging methods exist, each contributing its own unique set of qualities to the blade.
Clay Tempering (Yaki-Ire)
Yaki-Ire is a traditional Japanese quenching technique that makes use of Yakibatsuchi, which is a combination of clay, ash, and water. Japanese bladesmiths apply this combination to the blade’s body but not its edge.
The portion of the blade not covered with Yakibatsuchi cools more slowly than the cutting edge during the quenching process. The bare edge contrasts in hardness with the Yakibatschi-coated rest of the blade. However, although the body becomes softer and more long-lasting, the edge becomes firmer and keeps its edge for longer.
A line, known as a Hamon, is formed as a result of this procedure. Hamon knives are the name for both kitchen knives and swords tempered with clay.
Difference Between Forged and Stamped Knife
There are notable production differences between forged and stamped blades. This article focused on the production process for forged knives, not stamped ones. Thereby demonstrating their uniqueness.
Stamped knives are made by cutting a huge steel sheet into smaller pieces, whereas forged knives are honed from a single piece of steel.
Despite being heat treated, forged knives traditionally had a higher quality than stamped knives, however, this is not always the case now due to advancements in technology and the usage of higher-quality steel. While it’s true that some stamped knives perform better than their forged counterparts, the steel used in forged knives is always of a higher grade. A well-forged knife will usually perform better than a stamped one.
Although stamped knives tend to be lighter, forged knives are typically more user-friendly and effective in the kitchen.
There are, however, benefits to using a stamped knife. Stamped kitchen knives are the most cost-effective option if you require many of them. However, since stamped knives aren’t as durable as forged ones, they lose their edge more quickly and require more frequent sharpening and honing. When compared to stamped knives, forged blades are noticeably better.
It’s important to try out a knife in the store to make sure it’s a good fit for the kind of cutting you’ll be doing. Select a knife, forged or stamped, that you feel confident using.
Finishing Up
Making a functional kitchen knife requires many steps. It’s not a quick or easy task; rather, it involves several steps. Most people have a newfound appreciation for and care for their knives after learning about the process involved in making them. After all, they are the most often used kitchen appliance and come into contact with nearly every food we consume.
