Sharpness and persistence are both opposite and interdependent. Sharpness and persistence refer to the maximization of retention under appropriate sharpness.
The last two articles introduce the factors that affect the sharpness and retention of tools and their causes, and put forward the technical measures to improve the sharpness and retention respectively. This paper intends to eliminate its theoretical analysis, keep the operation method, and make appropriate merger and summary to facilitate reading.
The content of this article only represents my humble opinion, and omissions and mistakes are inevitable. Please forgive me and correct me.
First, a few problems that novices should pay attention to
1. Sharpening a knife is a job that requires patience, time, skill and even talent.
Even if you use a fixed angle sharpener, you can only solve the problem of fixed angle (the most difficult technology to master in sharpening), but other requirements are indispensable. Polishing a sharp and durable tool still requires patience, time and correct operation methods. Whether it meets the technical requirements of sharpening is the best standard to test the advantages and disadvantages of the sharpener, which is not to say that it is simple or complicated. The quick sharpener is the simplest, but its essence is scraping rather than grinding, and its effect is very poor, its sharpness is close to rough grinding, and its retention is even worse.
2. The use of fixed angle sharpener is still inseparable from the knowledge of sharpening technology.
Sharpening a knife with a fixed angle sharpener still belongs to the field of manual sharpening. If you are not familiar with the relevant knowledge of sharpening technology, you will not be able to judge and compare the advantages and disadvantages of fixed angle sharpeners when purchasing, and of course you will not be able to use them well.
3. The blade angle should be suitable for the purpose of the tool.
Too small blade angle is not durable and easy to roll or collapse. The blade angle is too big and not sharp, so it is difficult to sharpen it. Slicing knives are generally at 30 ~ 40 degrees, chopping knives are generally at 40 ~ 50 degrees, and bone cutters are generally at 50 ~ 80 degrees.
Too sharp a knife is not durable, so enough is enough.
Too sharp tools have too small cutting edge radius and insufficient strength, and are easy to curl and become dull, so it is necessary to master simple cutting edge passivation technology.
Second, tools and materials for sharpening knives.
There are many kinds of abrasives and abrasives, and their understanding is also very different. The following is just a summary of personal experience, shortcomings and deficiencies, please advise.
1. diamond file
Mainly used for cutting and grabbing superhard tools. In use, the generated iron filings should be cleaned up in time to avoid scratching the blade body (near the inner edge line); Don't file too much, lest there be a serious gap on the blade; Don't be too strong. Dipping in water can prolong the service life of diamond file.
Blade scratch and blade clearance caused by improper use of diamond file are shown in the following figure.
2. Ordinary oilstone
There are many kinds of oilstones, so the variety and granularity of oilstones should be determined according to the material and grinding task. When buying oilstone, you must choose qualified products. The inferior whetstone is either too hard or too soft. If it is too hard, the self-sharpening is poor, the particles are not sharp, and it is easy to strain the blade, resulting in scratches on the surface of the blade and cracks in the blade. Moreover, the grinding speed is extremely slow. If it is too soft, it will be consumed too quickly, and the grindstone will soon sag and cannot be used. At the same time, don't be superstitious about high-grade oilstones. This kind of oilstone is very professional, with strong pertinence and extremely harsh conditions of use. High cost may not achieve the best results.
As far as routine use is concerned, it is recommended to use green carbon oilstone, which is soft in texture, strong in cutting, good in self-sharpening, not easy to block, suitable for both soft and hard tools, and affordable, but has the disadvantages of high consumption and easy to sag. Mainly used for rough grinding (180 # ~ 320 #), medium grinding (600 # ~ 800 #) and fine grinding with good quality (1200 # ~ 1500 #). It should be fully soaked before use, and the dents should be leveled in time.
3. Ruby grindstone
The particle size is about 3000#, which can produce higher sharpness, thinner edge line and good retention. However, the technical requirements for operation are very high, and the hands should be stable and the angles should be consistent. If you can't do this, and there is no professional angle grinder, it is not recommended. Foreign bodies and iron filings on the surface of ruby oilstone should be removed in time to avoid damaging or blunting the cutting edge. A small piece of fine sandpaper can be dipped in water and wiped evenly along the whole surface for several times, and then washed with clear water. Depending on the amount of grinding, it may be cleaned several times during grinding.
The appearance of ruby oilstone is very important, and the price gap is also very large. The surface of high-grade ruby oilstone should be smooth, free of pores and uniform in particle size. Generally, the pores on the surface of ruby oilstone should be as small as possible, and the surface should be smooth. Because the price is relatively affordable, it is recommended.
4. Sharpening solution
When sharpening a knife, a knife that loves rust can only use oil. It is recommended to use water for other knives and dry them in time after grinding. Adding a small amount of detergent (soapy water can also be used) to water can enhance the adsorption capacity of oilstone, make it easier to stick to the knife, and form a dense water film on the knife body, thus reducing the requirements for the cleanliness of the knife.
5. Leather and polishing wax
Cowhide is commonly used, and cotton cloth can also be used instead. It is mainly used for finishing tools, thoroughly removing burrs, strengthening cutting edges, and also for polishing.
All abrasive tools should be cleaned up in time after grinding, and the sunken oilstones should be kept well after leveling to facilitate the next use.
Third, the method of sharpening the knife
According to the difference between moving the knife and moving the grindstone, there are two ways to sharpen the knife.
1. Fix the grindstone and move the tool.
This method is very common and can have a good hand feeling, but it can't directly see the contact between the blade surface and the grindstone surface, and the slurry produced by grinding is not easy to lose, which is beneficial to improve the grinding quality. When stopping grinding and readjusting the angle, it is easy to bring big errors, and the technical requirements for operation are relatively high.
2. Fix the cutter and move the oilstone
It is also an important method to put the knife on the table and drag the stone mill. Almost all fixed angle sharpeners are used in this way. This method is just like a fitter machining a workpiece with a file, which can visually see the contact between the edge surface and the grindstone surface, and can see the grinding situation after each drag, but the mud produced by grinding is easy to lose, and even local dry grinding phenomenon occurs, which needs supporting measures to make up.
Fourth, the method of sharpening the knife.
1. grinding technology
Technique is still the most important, including the following two aspects:
(1) Fixed grinding angle
Not only should the sharpening angle be fixed during the knife pushing process, but it cannot be changed when the angle is determined again after the pause. It must rely on a pair of stable hands and long-term practice.
As a novice or a person with poor skills, you can use reference objects or measuring tools to ensure that the grinding angle is consistent before and after switching. For example, find several feature points on the edge ridge, number them in sequence, then draw mark lines perpendicular to the cutting edge as far as possible on both sides of the blade body, measure the distance from the mark points to the cutting edge one by one, calculate the required height value according to the trigonometric function, record the corresponding serial number, and determine the angle with the corresponding height value when sharpening the knife, as shown in the figure.
It is best to push the knife in the same direction as the scribing direction. Every time the angle is determined, adjust the posture of the knife to be close to that before switching, then measure the height of the marked point with a ruler, and start pushing the knife after reaching the calculated value.
This method needs to mark and measure the fixed angle repeatedly, but the sharpening effect is worthy of recognition, even surpassing many experts, so it is especially suitable for novices.
⑵ The knife pushing direction is correct and stable.
Blade shape has a great influence on the retention of blades, which must be paid great attention to. The sliding direction of the tool on the oilstone should move from the cutting edge to the edge line, and be perpendicular to the cutting edge as much as possible, so as to produce a longitudinal edge line (the arc cutting edge is allowed to have oblique edges) and avoid harmful X edge lines and horizontal edge lines. The correct way to push the knife is shown in the figure.
When the tool has an arc edge, the sliding direction of the tool is different and the effect is very different.
In the first case, the sliding direction is always perpendicular to the cutting edge and a fixed grinding angle is maintained. This method is easy to master, because when two sides of the oilstone pass through the same position, the edge lines are not parallel, so there will be many X edge lines. In order to reduce the adverse effect of X-edge particles on retention, fine oilstone (such as ruby oilstone) can be used to make the edge particles as small as possible.
In the second case, the sliding direction is only perpendicular to the straight edge of the tool and always remains the same. This method belongs to variable angle grinding. The biggest advantage of this method is that the profile lines are parallel to each other, both longitudinal profile lines and oblique profile lines, and there is no X profile line. However, it is impossible to do it by hand without special sharpening tools.
2. Strength control
It includes the following two aspects:
(1) Master the sharpening strength and knife pushing speed.
The recommended strength for each grinding process is as follows:
Rough grinding: micro → light → heavy → light → micro.
Medium grinding: micro → light → micro
Fine grinding: tiny → tiny → tiny
The operation intensity of each process is from small to large, then maintained, and then gradually reduced. This is because at the beginning, the contact area between the grindstone and the cutting edge is very small, so it can prevent the cutting edge from being scratched and protect the grindstone by operating with small force. With the progress of grinding, the joint area between oilstone and blade also increases, and the strength also increases. When the sharp area is about to appear, the strength should be reduced to prevent the whetstone from scratching the cutting edge, causing burrs in advance and reducing wear marks.
While controlling the strength, we should also pay attention to controlling the speed of pushing. The slower the pushing speed, the weaker the local impact, which is more conducive to blade thinning and reducing blade defects, which is particularly important in the fine grinding stage.
⑵ Make full use of elastic buffering.
First, we should make full use of the elastic buffering effect of the blade body to prevent scratches on the blade surface and gaps on the blade that are difficult to repair. It is suggested to add a thick pad between the hand and the knife, or install a thin auxiliary blade.
Second, we should make full use of the elastic buffering effect of the blade to prevent the blade from being scratched or scratched.
Third, we should make full use of the elastic buffering effect of oilstone and its particles to prevent the cutting surface and edge from being scratched and weaken the wear marks. It is recommended to use smooth, soft, sharp and light oilstone with a cushion under it.
3. Blade shape control
It mainly includes the following three aspects.
(1) blade symmetry inspection and control
Except for a few partial edges, most tools require symmetry on both sides. When sharpening a knife, always check the symmetry of both sides of the blade, and pay attention to switching the sharpening position and rotating the knife body in time.
⑵ blade shape consistency control
The blade lines are required to be neat and smooth, so as to ensure the stress balance of adjacent parts and prevent snake-like stress.
(3) trimming
The closer to the cutting edge, the smaller the grinding force, and this uneven grinding will easily lead to the distortion of the edge surface, so the actual edge angle will become smaller. In the grinding process, the grinding force at the cutting edge is very small, so the serious defects formed when the force is large are not easy to eliminate, and there is a tendency to expand. Using fine oilstone (ruby oilstone is the best) perpendicular to the cutting edge, lightly grinding along the whole edge for several times, the virtual edge can be ground off and the defects can be repaired, and then continuous light grinding with fine oilstone can obtain good grinding effect. As shown in the following figure, cut off the part above the cutting edge shear line to repair the defect at this position.
It is suggested to remove the virtual edge in the clipping line shown in the above figure. When lightly grinding with fine oilstone, attention should be paid to cleaning off the burrs falling off the edge to prevent damage to the edge. Be sure to grind it lightly, otherwise the cutting edge will have serious defects.
4. Suitable abrasives
The role of abrasive is to remove the wear marks and defects left by the previous process to the maximum extent, and to minimize the new wear marks and defects. Its performance and effect are also reflected in these two aspects.
The most commonly used abrasives are oilstone, sandpaper and polishing wax. Correct selection and use of these abrasives is the key to realize the above functions.
First of all, the abrasive used should be suitable for cutting materials and grinding tasks;
Second, the use method must meet the technical requirements of grinding.
Third, fully explore the potential of abrasive and maximize its performance, thus reducing the grinding cost.
5. Blade strengthening
Machining the sharp, serrated, irregular and unsmooth cutting edge of the tool into a specific shape. This process is generally called "edge strengthening" or "passivation". In some applications, properly strengthening the blade can increase the tool life by 200% or more.
Knife is a simple and easy method to strengthen the cutting edge. With leather (cloth) and polishing wax (toothpaste and grinding paste) as tools, the following two purposes can be achieved:
(1) completely remove burrs.
When finishing the tool, the leather coated with polishing wax is completely attached to the blade, which is sticky and easy to completely remove the residual burr after fine grinding.
(2) Dressing, removing tiny serrations and passivating the blade.
When cutting, the defective micro-serrations can be completely removed and the micro-cracks on the cutting edge can be repaired. When the tool is too sharp, the application needs can be met by reducing the sharpness of its cutting edge.
Verb (abbreviation of verb) conclusion
Sharpening a knife must rely on a pair of steady hands, especially patience and perseverance.
When sharpening a knife, the cutting edge should not be worn too thin. At the same time, efforts should be made to make the edge lines parallel to each other and perpendicular to the cutting edge as far as possible to avoid X-shaped edge lines and horizontal edge lines. Therefore, we need higher operation technology.
⑶ Choose a pencil sharpener carefully. A good sharpener can really help you solve the problem of sharpening knives, and with the continuous improvement of your sharpening level, your dependence on it will be further enhanced. A poor sharpener, though professing to be professional, has many shortcomings and low performance, and is usually only useful for novices. Once your level is slightly improved, you are no longer willing to use it. It is suggested that you must be familiar with the related technology of manual sharpening before buying, find out whether the sharpener meets the technical requirements of sharpening and identify it carefully.