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How To Sharpen A Knife
Sharpening a knife is a skill well worth mastering to keep your knives at an optimum performance level and when sharp they are always much safer to use than when they are blunt.
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To sharpen your knife you will need to grind and hone it on sharpening stones, whetstones (the word "whet," meaning to sharpen a blade) and waterstones, the abrasive surface of these ‘stones’ is measured in grits. The number of grits indicate the density and size of the particles. However the grits are numbered differently depending on which part of the world they come from, but generally the higher the grit number the higher the density and the smaller the particles and finer the grit. Sharpening a knife entails working through starting from a coarse grit to a fine grit, depending on how blunt or damaged the blade of your knife is. A very coarse grit; 80 – 400; is for the fast removal of metal, and you knife may not need this every sharpening session. Medium coarse grits; 700 – 2000, are for refining the edge and removing the burr and fine grit stones; 3000 to 8000 grit; are for the final honing, removal of burr and polish. Whetstones are made from a range of abrasive materials traditionally natural quarried stone and the more recent artificial blends. They can be used with both oil and water. Waterstones need to be soaked in water before use and lubricated with water throughout the sharpening process. (oil will harm them.) Each stroke with the knife across the surface of the stone breaks away a small amount of particles constantly exposing new and sharp particles and building up a good slurry like paste of loose grit which is the mechanism by which waterstones sharpen a blade. Sometimes used in conjunction with waterstones are the specialized ‘Nagura waterstones ’which have a fine 4000, 6000, 8000 and 10,000 grit, these help waterstones build up a good slurry and are also used to level them, which should ideally be done before every sharpen alternatively. Diamond Hone Sharpening Stones comprise a steel plate sometimes with a plastic or resin base. The plate is coated with diamond grit.Nagura waterstones should also be saturated before you use them and a recommended method is to rub the flattening stone over the sharpening stone in a figure of 8 pattern. A course grit diamond honing stones can also be used to do the same thing. When sharpening your knife, lay the bevel of the blade edge flat on the sharpening stone. There are two popular methods of sharpening one is… Keeping that angle, push the blade across the stone away from you in shaving motion. Another popular pattern to follow with the blade is a figure of eight. |
Continue to do this splashing the stone with water from time to time, when you notice it drying out, to keep the slurry forming. Then move onto a finer grit. Repeat this motion a dozen or so times then turn the blade over and sharpen the opposite face towards you.
The angle at which you hold your knife needs to stay consistent, to help with this, some sharpening systems are designed to hold the blade at specific angle. One of these is the bevel guiding clamp style tool which holds the blade in place and the stone on a movable pre-set angle mounts for guided strokes. Another is where two sticks are fixed to a base in a V shape (See the Spyderco Sharpmaker in our camping and cooking section). The knife is held perpendicular to the base and pulled up the V. You will not be able to see the edge of a very sharp knife with the naked eye, but to see the reflection of the edge and catch sight of Knicks hold the blade to the sunlight. The Strop: Finish up your sharpening session with a strop. The strop is traditionally leather, ideally with abrasive compounds impregnated into it or just a piece of leather, smooth wood, or even cloth, this removes any burr or curl that has developed during sharpening, improving without disturbing the edge you have already achieved, and polishes too. Rub the blade across the strop surface a good few times until you are satisfied that it the honing is complete. |
| If your knife becomes blunt it becomes dangerous and ineffective so keeping a keen edge on it at all times is well worth the effort. Each knife has it's own blade characteristics and will require a little practice to master your specific knifes sharpening technique. Survival type knives typically have a thick blade for added strength and durabiltiy which can make the sharpening process more tricky, the angles are larger on a thicker blade and too thin a cutting edge is vulnerable to chipping and breaking. |
| Steel Element Information
Carbon (C) Increases edge retention and raises tensile strength. Increases hardness and improves resistance to wear and abrasion. Chromium (CR) Increases hardness, tensile strength, and toughness. Provides resistance to wear and corrosion. Cobalt (CO) Increases strength and hardness, and permits quenching in higher temperatures. Intensifies the individual effects of other elements in more complex steels. Copper (CU) Increases corrosion resistance. Manganese (MN) Increases hardenability, wear resistance, and tensile strength. Deoxidizes and degasifies to remove oxygen from molten metal. In larger quantities, increases hardness and brittleness. Molybdenum (MO) Increases strength, hardness, hardenability, and toughness. Improves machinability and resistance to corrosion. Nickel (NI) Adds strength and toughness Nitrogen (N) Used in place of carbon for the steel matrix. The Nitrogen atom will function in a similar manner to the carbon atom but offers unusual advantages in corrosion resistance. Phosphorus (P) Improves strength, machinability, and hardness. Creates brittleness in high concentrations. Silicon (SI) Increases strength. Deoxidizes and degasifies to remove oxygen from molten metal. Sulfur (S) Improves machinability when added in minute quantities. Tungsten (W) Adds strength, toughness, and improves hardenability. Vanadium (V) Increases strength, wear resistance, and increases toughness. Steel Production And Properties The following provides a very brief overview of steel treatment and properties: By definition, steel is a combination of iron and no more that 2% carbon. Steel is alloyed with various other elements that combine to produce special properties. Once a particular alloy combination (or steel type) is selected, specific procedures are used to maximize the unique qualities required for that steel to perform. Generally speaking, the process for converting a steel alloy into a premium knife steel is heat treating. Heat treatment is the most important stage in the evolution of an alloy into a performance knife steel. The first step in the heat treatment process is to reach a critical temperature. This temperature is held for a specific amount of time (depending on the steel being hardened) and causes the steel to become austenetized. Heat treatment is one of the many factors that determines the grain size of the steel (a fine grain structure is more desireable for knife blades because it improves edge retention and enhances blade finish). Next, the steel is quenched to achieve its maximum level of hardness. At this point, the steel is too hard and brittle for practical use and thus tempering is of key importance in bringing the steel to its ideal hardness level (different knife steels perform best at different levels of hardness). | 
Tempering also increases wear resistance and toughness properties. When tempering, it is important to understand the interaction between hardness and toughness. An increase in yield strength and tensile strength and a decrease in impact strength and ductility. An increase in toughness is usually accompanied by the opposite effect (i.e. an increase in toughness and ductility and a decrease in yield strength and tensile strength). Therefore, high-impact knifes such as swords and machetes would benefit from a softer blade (to avoid blade breakage), while low-impact knifes such as pocket knifes may benefit from a harder blade (to improve wear resistance). Once tempering is complete, the final hardness of the steel can be determined using a Rockwell Test. For more detailed information of the above processes and properties, we recommend the following references that were used to compile this information: Metallurgy Fundamentals by D.A. Brandt (published by Goodheart-Wilcox) and Heat Treaters Guide by P.M. Unterweiser (published by ASM). Alloy: A material that is dissolved in another metal in a solid solution; a material that results when two or more elements combine in a solid solution. Austenetized: The basic steel structure state in which an alloying is uniformly dissolved into iron. Critical Temperature: The temperature at which steel changes its structure to austenite in preparation for hardening. Ductility: The tendency of a material to stretch or plastically deform appreciably before fracturing. Grain Size: The physical size of the austenite grains during austenizing. The actual size can vary due to thermal, time and forging considerations. Hardness: The resistance of a steel to deformation or penetration analogous to strength. Heat Treating Heating and cooling metal to prescribed temperature and the limits for the purpose of changing the properties and behavior of the metal. Impact Strength: The ability of a material to resist cracking due to a sudden force. Quenched: Rapidly cooled from the critical temperature using water, oil, air or other means. Rockwell Test: A measurement of steel hardness based on the depth of penetration of a small diamond cone pressed into the steel under a constant load. Tempering: Reheating to a lower temperature after quenching for the purpose of slightly softening the steel, precipitating carbides, stress relieving. Tensile Strength: Indicated by the force at which a material breaks due to stretching. Toughness: The ability of a material to resist shock or impact. Yield Strength: The point at which a steel becomes permanently deformed; the point at which the linear relationship of stress to strain changes on a Stress/Strain curve. |
