How to sharpen the knife, how to sharpen the knife the fastest

At present, there is no unified industry standard for the sharpness detection of commonly used tools, which is usually determined according to the specific performance of the tool in paper pushing, shaving and hair breaking. From the analysis of the structural characteristics of the blade, the sharpness of the blade mainly depends on the following five important factors.

1. Edge Angle

The smaller the edge Angle, the sharper the edge, the smaller the cutting resistance, and the higher the sharpness, which is an important factor affecting sharpness.

2. Edge radius

The smaller the radius of the cutting edge, the smaller the cutting pressure, and the sharper the nature, which is the most critical element to make the tool sharp.

3. Knife-edge pattern

The edge grain direction is the same as the cutting direction, it is easier to cut, and it is sharper, and the edge grain is parallel to each other and perpendicular to the cutting edge (longitudinal edge grain). The micro-serrations produced at the edge of the blade are also conducive to improving sharpness.

4. Rough selvedge

The raw edge will greatly increase the cutting resistance of the blade, which is an important factor affecting sharpness, and the sharp blade should have no raw edge.

5. microserration

Strictly speaking, the edge is slightly serrated, and when the teeth are in the same direction as the cutting, the smaller the cutting pressure, the sharper the blade.

Second, the relationship between knives and sharpness

The same knife, the same sharpening method, why the small Angle sharpening is much sharper? (The mechanics of the wedge alone cannot be explained at all)

The same grinding method, the same grinding Angle, the same material and heat treatment, why the sharpness of different shapes of the tool is very different?

Why are stainless steel knives more difficult to grind?

Why is the positioning error of the hand at least a few millimeters, and the grinding edge can be as thin as a few microns?

To find answers to these questions, watch for the following analysis.

1. How to minimize the radius of the cutting edge?

Among the five main factors that determine sharpness, the edge Angle is determined in advance, the micro serration is mainly related to the material, and the cleaning of the raw edge is a post-processing, therefore, the sharpening of the knife needs to focus on reducing the radius of the cutting edge as much as possible and producing the longitudinal edge of the two problems. In order to obtain the smallest possible radius of the cutting edge, the key is to try to delay the rolling edge as much as possible (because once the rolling edge will produce a raw edge, continue grinding will only make the raw edge expand, it is difficult to further reduce the radius of the cutting edge), so the following two points must be done.

⑴ local micro-force cutting

Each stone particle must cut the blade with very little force in order to prevent premature curling.

⑵ local micro cutting

The cutting amount of each oil stone particle on the blade must be very small, otherwise it will produce a large number of scratches on the cutting edge, thereby reducing the strength of the cutting edge, resulting in early crimp of the cutting edge. In addition, the larger cutting amount is accompanied by a larger cutting force, which is also an important reason for inducing the winding.

In order to achieve the above two points, we must try to avoid stress concentration, because it will lead to local cutting force and cutting volume increase, resulting in premature defects such as burring and scratches at the cutting edge.

2. Buffer protection mechanism of grinding process

Due to the limitations of flatness, particle size uniformity, sharpness difference, incomplete fit with cutting edge, grinding Angle error, etc., the buffer protection mechanism is indispensable to achieve local micro force and micro cutting. The more effective the buffering, the better the sharpening effect, and the cutting edge is easier to thin, on the contrary, it can not make the cutting edge thin, and even serious defects such as blade notch and scratch may occur.

(1) The protective effect of the elastic deformation of the tool body on the cutting edge

The protective effect of the tool body elastic deformation on the cutting edge is simulated in order to explain the formation mechanism and important role of the buffer protection mechanism.

The blade knife is pressed on the oil stone with a very small force, the edge surface is completely fitted with the oil stone, and the deformation of the tool body is negligible, which is the standard sharpening state. The ridge height of the tool is 84.51mm, the midpoint height of the tool belly is 42.26mm, and the actual sharpening Angle is 25. (Blade Angle 50.) The sliding friction direction of the blade is from left to right

If the Angle and posture of the above picture are always maintained, a very thin cutting edge can be obtained by continuous light grinding. However, because the hands always have a certain amplitude and asynchronous swing, the following five different situations are caused.

In the first case, the operation is very small, but the hands are raised, and the actual sharpening Angle is also increased, only the cutting edge is sharpened, and the edge surface is not sharpened. Because the operation force is very small, even if this happens occasionally, as long as it is a small amount of cutting, it generally does not cause the blade to roll in advance, but it also limits the improvement of sharpness.

In the second case, both hands are reduced, the actual grinding Angle is reduced, no matter whether the force is applied, it can not grind the edge and the edge surface, but only the inside edge line, in this case, although the edge line will be rounded, but there is no damage to the edge.

The third case, keep the height of the knife ridge unchanged, and press the hand of the knife belly due to instability resulting in a sudden increase in strength, the knife belly then suddenly sank, due to elastic deformation, the knife belly sank resulting in the tip of the knife raised 2.620. The actual grinding Angle is reduced to 22.210. The increased force is transferred to the inside edge line through the knife body, although this will cause the edge line to be rounded and not neat, but it effectively protects the cutting edge.

In the fourth case, the height of the knife belly is maintained, and the unstable hand of the knife leads to the warping of the knife ridge. Due to elastic deformation, the warping of the knife ridge not only does not increase the Angle of sharpening, but makes the tip of the knife warping 1.323. The grinding Angle is reduced to 23.899. The situation is very similar to the third situation, which can also protect the cutting edge. (Of course, if the upwarping amplitude is too large, it will drive the belly of the knife to rise, and the sharpening Angle will therefore increase, which is harmful to the cutting edge)

The fifth case, because the oil stone is not smooth enough, and the particle size is not uniform, the edge will be affected from time to time, the elastic deformation of the tool body will also make the edge upwarped, so as to avoid or reduce the direct impact on the cutting edge, which is conducive to improving the sharpness.

It can be seen that in the third to fifth cases, due to the elastic deformation of the tool body, the impact generated during the operation is effectively buffered and transferred, and the smaller the coefficient of stiffness, the better the buffering effect, and the better the corresponding grinding effect. This also explains the phenomenon that "the thinner the knife, the easier it is to sharpen". When actually sharpening the knife, the elastic deformation of the tool body is usually not so large, but the basic principle is the same.

The principle of cushioning protection of elastic deformation is not only widely used in traditional manual sharpening, but also applied in the contour constant Angle sharpener, and it has the characteristics of accurate fixed Angle, avoiding the first adverse situation, and the sharpness of the cutting tool is much higher than that of pure manual operation. The principle of protecting the cutting edge of the contour constant Angle sharpener

Other fixed-angle sharpeners do not have this protection mechanism (3×6mm steel instead of a 4mm diameter guide rod, the strength of the two is similar).

(2) The protective effect of the elastic deformation of the cutting edge

In the grinding process, the blade directly bears the impact of abrasive, and the influence of elastic deformation is greater. Below is the same tool, the edge Angle is 60. And 30. Comparison of the contact between the edge and the oil stone.

Due to the lack of corresponding data, logical reasoning is performed. As you can see from the figure above, the edge Angle is 60. The edge is much stronger, its side strength is high, it is not easy to deform, and there is almost no bullet *, so in the grinding process, the impact of the cutting edge and the oil stone particles is also much larger, which is obviously not conducive to reducing the radius of the cutting edge, which will inevitably lead to premature rolling. And the edge Angle is 30. The edge is quite thin, the side strength is very low, easy to deformation, there is an obvious bullet, the impact in the grinding process is much smaller, can effectively avoid early curling, so it is conducive to reducing the radius of the cutting edge.

I have experimented with the same front hacksaw blade. One of the blade angles is 30. The ground blade can cut the hair in the air, and it is observed under an 80-fold microscope, and the cutting edge is a thin line that is almost absent, which is estimated to be 1 micron or less. The other edge Angle is 60. The grinding out of the blade can be shaved but not very smooth, placed under the 80-fold microscope observation, the cutting edge is an uneven obviously thick white line, with a reading microscope to measure its thickness of about 5 to 10 microns.

According to the above analysis and the actual grinding test, it can be seen that with the increase of the edge Angle, the sharpness also decreases sharply, although there are mechanical principle factors of "splitting", but more importantly, because the radius of the cutting edge increases sharply. This is also the main reason why the smaller the blade Angle, the better the grinding.

(3) The elasticity of the oil stone and its particles protects the cutting edge

The use of flat, soft and sharp stone is conducive to improving the sharpness of the tool, which is a very important common sense, it can enhance the ability to fit with the blade, prevent the damage of stress concentration on the cutting edge, and also attenuate the damage caused by hand instability on the cutting edge.

In order to make the oil stone and its particles more elastic *, it should be chosen to be flat and fine, soft and thin. Lay the stone on a soft mat and push the tool as slowly as possible while sharpening the knife. Practice has proved that the fine sandpaper is quite ideal grinding material, its surface is flat (pad on the flat substrate), soft and thin texture, is difficult to compare with other oil stones, so it is especially suitable for the late grinding, but its disadvantage is that the grinding amount is very small, the operation requirements are also high, pure manual operation is very difficult.

3. The relationship between blade shape and sharpness

The blade shape includes features such as outline and edge Angle. Here are 13 common cutting edge shapes of knives.

(1) is a form of cutting tool used by the vast majority of manufacturers, the knife body strength is high, easy to grind, the grinding technology requirements are low, but it is not easy to be very sharp. The common kitchen knife is this kind of cutting edge form, and there are also many dagger knives.

(2) The use of concave grinding technology, can also be said to be the deformation of No. 1, the knife body concave, thin blade, can reach a high sharpness *, but when the blade is sharpened thick, sharpness also decreases accordingly. Many folding knives use this cutting edge shape, knife friends on the Internet to show sharpness is mostly this type of knife.

(3) No. 4 is more common in manual knives, such as Tang Dadao and Japanese samurai sword. This type of blade Angle is very small, the blade surface orientation is good, so it can be ground extremely sharp, far from (1), (2) comparable, especially when cutting the penetration is very high, but the disadvantage is that the strength of the knife body will be reduced because of the very small cutting Angle, which is easy to cause a notch or rolled edge. However, if the blade is not high-intensity work, it can maintain a high sharpness even after wear. However, this kind of blade has a serious disadvantage, after the wear and tear of the blade regrinding is very time-consuming and laborious.

(5) The deformation of (3) and (4) is only the change of the integral blood tank formed by the inner arc tool body. For example, Mongolian knives, security knives and other Chinese ethnic manual knives often use this type of blade. Due to the existence of the blood slot, the blade surface is greatly narrowed, and the orientation is therefore worse, so the grinding difficulty is slightly greater, the sharpness is reduced, but the workload of grinding is also greatly reduced.

6 Blade is very rare, the main example is the old razor, in some ancient Western swords are also found, this blade is difficult to maintain its original appearance after grinding itself often converted into a 5 blade. This kind of blade is extremely thin from the belly to the edge, and the edge Angle is very small, so it is easy to grind, and the sharpness is far from that of other cutting tools with edge shapes.

The blade can be said that the whole blade is the blade, which is more common in special purpose knives that need to be extremely sharp, but it is often found on the kitchen knife this grinding method (also different from the knife, some people will grind the kitchen knife completely flat on the stone grinding will form this blade). This blade is extremely sharp, mainly due to the very low grinding Angle and excellent orientation of the wide edge surface.

The ⑻ is curved, the knife body strength is high, easy to grind, but the sharpness is not very high. Mostly seen in large Tibetan knives, ancient Chinese flat made single-handed knives... .

(9) The blade surface is the edge, this kind of blade is more common in carving knives, chisels, peeling knives, scissors and other special purpose tools. This structure will greatly facilitate grinding, eliminating the trouble of backhand grinding. However, there is an obvious skew phenomenon when the tool is stressed, that is, the blade is greatly offset to the flat side, so the fighting tool is rarely used.

(11), (12), and (13) are ways of grinding the back of a knife. The purpose of this blade is not to cut, but to guide the blade when piercing, so sharpness is generally not pursued.

The relationship between shape and sharpness can be well explained according to the elastic deformation theory of the blade and the blade, the smaller the edge Angle, the thinner the blade, and the higher the sharpness. In addition, the wider and straighter the blade surface, the better the orientation, and the easier it is to find the feeling when grinding, thus reducing the Angle error and making it easier to grind.

Third, the relationship between blade material and sharpness

The impact of the characteristics of the blade material on the sharpness, still need to be explained from the local micro and micro cutting, where it is favorable, it is conducive to the improvement of sharpness, on the contrary, it will limit the sharpness, and the final sharpness is the result of the combined effect of these favorable and unfavorable factors.

1. The material is especially good for sharpness

(1) Fine and dense grain

The radius of the cutting edge is limited by the grain size, and the grain is small and dense, so it is possible to grind out a particularly thin blade. Especially sharp tools, the grain structure of the material is fine and dense.

⑵ ultra-wear-resistant

Super wear resistance is a more favorable factor than high hardness, due to wear resistance, the cutting amount must be small, the friction is also small, the corresponding cutting force is also small, the local cutting amount and cutting force are very small, obviously conducive to improving sharpness. The cutting tool made of bearing steel has thinner cutting edge, micro-serrations, first-class sharpness and good retention.

⑶ High hardness

Hardness will affect many properties of steel, including wear resistance, strength and so on. Material hardness is high, should be equipped with high hardness and sharp abrasive grinding, abrasive particles embedded very shallow, local cutting amount and cutting force are very small, so it is conducive to improving sharpness. Very sharp tools, most of them have the characteristics of high hardness. The razor blade's edge is superhard ceramic coating, and its sharpness is undoubtedly very high.

⑷ High elastic *

The high-elastic material has a strong return ability, which is good for buffering local impact, and the cutting edge is not easy to curl, which is conducive to improving sharpness. Knife made of spring steel, sharp is also good.

⑸ pattern

Historically, the sharpest known Damascus steel knife is a "cast pattern steel", which can cut a hair in the air, showing the effect of its pattern on sharpness.

2. Materials that hinder sharpness improvement are special *

⑴ Strong plastic *

Strong plasticity means that it is easy to roll the mouth, and due to the driving role of the raw edge, the formation of a vicious circle to further aggravate it. Therefore, the plastic tool is very strong, the rough edge formed is thick and wide, and it is not easy to fall off, of course, is not conducive to the improvement of sharpness.

⑵ High viscosity

High viscosity, the grinding friction is large, the local cutting force is also large, the local cutting amount can not be kept small, so the improvement of sharpness is also unfavorable.

Common stainless steel has unfavorable conditions such as strong plastic and high viscosity, so it is more difficult to grind, which is also the main reason why many people feel that stainless steel knives are not good to use. On the other hand, stainless steel also has the advantages of high hardness, high strength, not easy to rust, as long as the use of appropriate grinding methods or tools, it can still be sharp and durable, so it is still widely used.

Four, how to sharpen the knife to sharp?

Generally speaking, as long as the blade is thin enough, the edge Angle is small enough, and the blade body material is not difficult to grind, it is not difficult to grind a particularly sharp blade. However, blindly reducing the edge Angle, without considering the application needs, this practice is not advisable for sharp and sharp. The pursuit of sharpness must meet the needs of the application, not at the expense of retention.

How should we sharpen the knife, from the above can already see the clues, now a simple summary.

1. Accurate and stable grinding Angle

About the Angle of sharpening, it is already a cliche, "seven points of the technique, three points of the abrasive", the core of the technique is the mastery and control of the Angle, which is a lifelong need to practice technology, visible its importance. Poor Angle control, so to speak, all the tricks