How to sharpen a knife with a bar: instructions and tips. Sharpening knives: expert advice

Household knives need sharpening from time to time. They begin to blunt especially quickly under increased lateral loading, when pieces of metal come off the edge, or when cutting hard objects at right angles. The main goal of sharpening household knives is to maintain sharpness as long as possible. cutting edge, removing from it when sharpening as little metal as possible. To achieve this, you need to know how to sharpen knives with a bar correctly, because this is the most common sharpening option at home.

Sharpening stones come in several varieties: diamond, ceramic, natural, Japanese water. In addition, sharpening devices are also electric type... Not having the skills to sharpen knives at home, it is better to use an ordinary abrasive or ceramic bar. Electric sharpeners can ruin the blade in the absence of the right skills or poor quality tools. In order to straighten the blade, you should use musat.

In order to sharpen a knife well, you must use at least two abrasive bars, one of which has a larger grain size, the second one smaller. The blade is sharpened with one sharpening stone and polished with the second.

The correct block should have a length of 1.5-2 times the length of the knife, its surface should be flat, without chips. For a start, it is better to purchase a stone of medium hardness, and when the necessary skill appears, purchase several different stones for different degrees of sharpening and type of steel. The best quality sharpening is still characterized by stones of Soviet production, if you managed to find such a bar somewhere on a flea market, then you were lucky, and the quality of sharpening with long term services are guaranteed.

In addition to sharpening knives with bars, goi paste can be used to form a sharp cutting edge. In order to have not only a theoretical idea, but also a practical one, it is better to watch a video on how to sharpen knives with a bar correctly.

How to sharpen knives with a bar by hand

When sharpening knives by hand, start with a coarse grit and finish with a fine grit. In doing so, it is recommended to observe the following principles:

The knives are sharpened in smooth movements, without pressure on the cutting edge.
It is necessary to pick up optimal angle sharpening and observe it throughout the entire sliding process on the bar.
Before the start of sharpening, during the process itself and as it ends, it is necessary to moisten the whetstones with water or soapy water. This is necessary for better sliding of the blade, in order to avoid clogging the pores of the stone with metal dust, as well as to get rid of the appearing dirt during the process and to clean the stone after sharpening.
The first attempt to sharpen the edge is best done on a knife that will not mind ruining it.
The grinding pass is made with the cutting edge forward, "away from you". Sharpening starts from the location of the handle. As the blade moves along the bar, the knife is pulled towards itself so that, reaching the end of the sharpening stone, at the same time it reaches the end of the point.
Ceramic knives are hard and retain their sharpness well after sharpening, but they are very fragile, unlike steel knives. Sharpening of this type of blades is carried out only with diamond wheels.

The process of sharpening household knives can be described step by step:

The bar is moistened with soapy water (you can use dishwashing liquid).
The stone is placed on a flat surface - a table, cutting board position convenient for you.
The desired sharpening angle is selected to fix the position of the knife. When sharpening it at a certain angle, it is worth remembering: the smaller it is, the sharper the cutting edge is, and the larger, the longer it will remain sharp.
For different types kitchen knives choose their own angle: for a regular knife it is 40-45 degrees, for a fillet knife intended for thin cutting of fish, poultry or meat, the sharpening angle should be 30-40 degrees. For other tools, there are values: 10-15 degrees for razors and scalpels; 15-20 - for cutting vegetables, bread; 25-30 - angle for sharpening hunting knives. To obtain the correct angle between the blade and the block, divide these recommended values by two. Thus, to sharpen a 45-degree edge, you need to sharpen each side of the blade at 22.5 degrees relative to the sharpening surface.
The knife is placed in such a position that the upper part of the handle is under the lower edge of the block. One hand adheres to the handle, the other - the cutting edge, then you need to start sliding the blade with a movement away from you from the bottom of the knife to the tip in the direction of travel.
The cutting edge must be perpendicular to the direction of travel.
The angle is maintained throughout the movement, with the knife handle raised at the bend of the blade to maintain a certain angle.
You will need to make at least 40-50 sliding movements on one side, then turn the knife over and repeat the same steps on the other side. A sign that the edge has begun to sharpen will be the appearance of the characteristic "burrs" on the blade. As you sharpen, metal dust will appear, which must be removed from the surface of the sharpening stone.
When the point is sharpened, it is necessary to start finishing the blade. To do this, you need to follow the same steps as described above, but on a stone with less grain. An alternative to such a bar will be musat. It is a steel round bar with longitudinal grooves for edge straightening. It is not suitable for sharpening, and for a knife that is too dull, it is useless, but it will help to edit the knife before and after working with it. To use the musat correctly, it must be kept strictly vertical. The blade moves along the musat at an inclination of 20-25 degrees no more than 4-5 times on each side of the blade.
If you need a razor-like sharpness of the blade, you can use goi paste. She needs to process the entire edge of the knife and repeat all the sharpening steps described above, with the only difference that sharpening is done in the direction from the cutting edge.

To simplify the sharpening process under right angle, special templates can be made. To do this, an angle of 30, 40, 45, 22.5 degrees is marked on thick paper using a protractor. A corner is formed from it in accordance with the desired value, and this corner is used to measure the position of the blade relative to the surface of the sharpening bar during sharpening.

How to sharpen knives with a bar: an alternative

If there is no desire or opportunity to use a sharpening block, you can sharpen the blade in alternative ways:

The easiest way is to sharpen the rough edge of the ceramic saucer underneath it. The principle of sharpening is the same as described above, the main thing is to observe the angle of inclination, direction and smoothness of movement.
Electric sharpener - convenient and quick way blade sharpening, can work even with very dull blades, including ceramic knives. Often used in places Catering to work with big amount tool. But the catch in its use lies in the fact that it removes too much metal from the blade, which leads to rapid wear of the knife. In addition, the electric sharpener is not the best cheap way sharpen the blade.
Roller knife sharpener. This is an inexpensive and simple method, but far from the most effective, because the sharpness of the blade does not last long. A mechanical V-shaped sharpener is also cheap and fast in terms of sharpening, but ruins the blade a lot.
Sharpening systems allow you to precisely adjust and maintain the required angle. Sharpening systems come with the ability to fix the blade and the sharpening stones themselves at a certain angle. The main disadvantage of these systems is that not all types of kitchen knives can be sharpened with them.

Sharpening the blade using an emery machine. It is effective but inconvenient for home use, and even more so, for a beginner, a way. Sharpening of the blade is carried out using several types of wheels: abrasive, felt, grinding. This method is often used to sharpen large hunting blades.

A knife is an indispensable tool for a hostess in the kitchen. Over time, the blade loses its sharpness, dulls and using it becomes torture. There are many ways to sharpen a knife correctly. The sharpness of the blade depends on the material, the well-chosen tool and the sharpening angle. The stores offer an assortment of hand and automatic devices allowing you to sharpen the blade yourself.

How to sharpen knives correctly

A sharp knife is the main condition for the efficient and safe work of a professional chef and housewife. During the cutting of products, small particles of steel are torn off the surface of the edge. The blade becomes dull, forcing more effort to cook. The sharpening process is the restoration of the geometric shape of the cutting edge. The choice of attachment for this purpose depends on the material of the knife and the skill of the grinder.

The arsenal of tools for restoring edge sharpness includes a set of accessories from a file to a universal automatic sharpener. The devices have different effectiveness, if used incorrectly, they will lead to damage to the blade. If you have nothing at hand but a file, use it with care. The tool leaves scratches on hard steel, and removes a significant layer of metal from a soft surface.

At what angle to sharpen the knife

There is no universal value for the sharpening angle. Its value varies depending on the material and purpose of the knife. Special and homemade devices will help determine the angle of the blade:

The edge is clamped with scissors, and the angle between the halves is measured with a protractor. The measurement error is 1.
Professionals use a special laser device with a scale.
In the factory and repair shops, the indicator is measured with a mechanical goniometer.

The optimal sharpening angle of knives differs depending on their purpose:

household kitchen knife - 30-35;
for fish processing - 25;
chopping - 25-30;
fruit - 15;
for processing vegetables - 35;
for felling - 40-45;
dining room - 55-60.

It is very important to choose the right hunting knife. There are many factors to consider: length, width, shape, handle and blade material, and sharpening angle. Much depends on the purpose of the knife.

Types of hunting knives

With all the variety of characteristics of the offered hunting knives, they can be divided into two groups:

Common uses that are used to finish off prey. Their blades are even, the handle is necessarily equipped with a limiter.
For special purposes (skinning, cutting meat from bone, butchering an animal or poultry carcass).

They are also subdivided according to the type of blades and the sharpening of the upper edge. It can be straight and rounded. Especially original in their performance Hunter knives self made.

Choosing a hunting knife

Currently proposed big choice hunting knives from manufacturers different countries. Russian manufacturers also are not inferior in quality and variety of the offered specimens. Their design is quite simple: a handle and a blade. The blade has a cutting part, which is called the blade and is subject to periodic sharpening. A cover made of durable and soft material (usually thick genuine leather with a wooden or plastic insert) is also very important for observing safety measures and ensuring safety. He must have a safety strap to prevent the weapon from falling out of the scabbard.

When choosing a hunting knife, you must be guided by the main characteristics:

The shape of the knife should correspond to the purpose of its use (the blade can be straight or curved).
The sharpening of hunting knives depends on their purpose.
The handle should be comfortable when cutting carcasses. It can be located either as an extension of the blade or at an angle to it. Make it out of various materials: wood, metal, birch bark, ceramics, plastic. In order to avoid slipping out of hands, it must have a stop.
The method of attaching the handle to the blade. A handle attached with a nut is much stronger than with glue.
Hunting knife blade material. The hardness of the steel depends on the carbon content. The most valuable brands are Damascus and Damask. For hunting knives it is considered optimal from 50 to 60 HRC (according to Rockwell). The steel must be anti-corrosion.
Blade length and width. The optimal length is considered to be 12-13, width is 3-3.5 cm.

Knife sharpening methods

Despite the hardness of the steel from which the knife is made, after a certain time its sharpness decreases. Therefore, it is necessary to periodically restore this function. Sharpening of hunting knives can be done different ways with help:

grindstone;
musata;
a set of tools;
special pocket sharpeners;
(mechanical, electrical);

It should be remembered: the smaller the sharpening angle of the hunting knife, the more delicate it is intended for. For hunting knives, it is 15-30 degrees. For example, for butchering and caving works - 30, universal - 20, for skinning and separation of meat from bone - 15 degrees.

As a rule, grinding machines are used at manufacturing plants and at special points for sharpening tools. But very often hunters carry out this on their own, using the other above-mentioned devices for sharpening hunting and

Sharpening a knife with a bar (stone)

Consider how to properly sharpen a hunting knife with a bar at home. When sharpening a knife in this way, you must choose a flat wide bar with a length of at least 25 cm with a non-coarse structure. In this case, you must follow the sequence of actions:

The block must be secured on a flat and stationary surface.
Lubricate with oil (vegetable, technical) or soapy water so that the metal crumb does not stick to the bar, wait a few minutes.
With smooth movements, start sharpening with a moistened bar, pulling the knife along it under pressure along the entire length of the blade. We perform this action on both sides in turn. In this case, it is necessary to observe the initial sharpening angle of the hunting knife.
The process must be repeated several times until a new one appears on both sides over the old edge.
Then the block is changed into a fine-grained stone and the finishing is done without pressure, with light sliding movements.

For a more convenient fixing of the sharpening stone, you can make a frame in the form right angle and fix the bar in it in an inclined position. You can use a special device for fixing emery with an adjustable slope.

To control the quality of the sharpening of hunting knives, you can try to cut a newspaper sheet in an upright position in one motion. The sharpening angle can be checked by in a simple way using ordinary scissors. It is necessary to take them in hand, insert a blade between them, gradually squeezing the blade of the knife. At the same time, for better visibility, direct them to a bright light (lamp) to ensure the compression density. Then carefully remove the blade and measure the angle between the scissors blades with a protractor.

Sharpening a knife with musat

Musat is a file with a round or cut on both sides with a handle. Very hard steel or diamond coated ceramics are used for its manufacture. Musatom usually only straighten blades that are not too dull. This ensures that the cutting edge is not damaged even after repeated use. If the knife has completely lost its cutting properties, then you cannot sharpen it in this way.

The process is carried out as follows:

one hand holds the musat in an upright position (on a non-slip surface);
in the other hand we take the blade at an angle of 15-20 degrees, extend it from top to bottom (from ourselves and towards ourselves) along the entire length of the blade (first from one side, then from the other side). Such repetitions should be made from 4 to 6. When using ceramic or diamond musat, once is enough.

Sharpening a knife with special kits and pocket sharpeners

The set for sharpening knives includes several stones with multi-colored handles, special guides and oil. The sharpening technology with these devices is simple and does not require special skills. Each compartment has its own angle of attachment. According to the color of the handles, the grain size of the whetstones is distinguished. When using this method, the sharpening of the blade is perfect.

Pocket sharpeners offered in specialized stores are small stones of various shapes(round, square, oval) that fit in the palm of your hand. As a rule, they are made from quality materials... They are located in special grooves made in a plastic case at a certain angle. It is convenient to take such sharpeners with you for hunting or fishing, as they are compact and easy to use.

Dependence of the sharpening method on the steel grade

For different brands not all sharpening methods are equally suitable. For example, the very popular Damascus steel knives cannot be sharpened on electric machines, since it has a heterogeneous structure. It consists of alternating soft and hard layers, so the blade should be sharpened with extreme care, otherwise the edge of the blade will become ribbed and will crumble in the future. Knives made of such steel should be sharpened by hand, gradually changing the grain size of the stones in the direction of decreasing.

Damask steel is characterized by increased hardness. Knives from it must be sharpened for a long time. In this case, electrical and mechanical machines are often used. It is necessary to start with coarse-grained stones moistened with water, gradually approaching fine-grained ones.

It should be noted that with the automated method of sharpening, it is not possible to achieve the sharpness and accuracy that is ensured by manual work. At the same time, the main advantage is the speed of this process.

Handmade hunting knives require a special approach when sharpening the blade, since they can be made from non-standard steel grades. Therefore, it is recommended to sharpen them by hand.

We conclude: correct sharpening hunting knives is a very important process to preserve appearance and durability. This hunting props should only be used for its intended purpose and remember to keep it clean, periodically lubricating it with oil (both blades and wooden handles) to prevent loss of shine and shrinkage.

In the kitchen, hunting or in any other business, you always need sharp knives... With the help of such tools, it is not only easy and pleasant to do something, but also the result is beautiful. There are many mechanical and electrical appliances, with which sharpening knives at home does not present any difficulties. However, all of them, rather, are intended for women.

The real man-owner will definitely use the good old method of manually editing the blade. This process is even more painstaking and longer, but the result will be completely different.

About steel

How high-quality sharpening will turn out will depend not only on skill, grinding materials, but also on steel. Its optimum hardness ranges from 45 to 60 HRC. A knife made from a softer material will have the cutting edge wrinkled easily, and from a harder material it will chip and dull. You can also determine the quality of the steel yourself, but this will require a new file. If, with light pressure, it will slide along the edge, and with strong pressure, it will slightly cling, then the hardness of the material is "correct".

Sharpening flat knives

The initial operation is performed with a coarse grain bar. They process the cutting edge of the blade on both sides until a burr appears along its contour - a thin strip of "excess" metal, which is bent in both directions. Then the knife sharpening at home continues with a finer-grained bar. With its help, traces from the impact of the previous donkey are completely removed, not paying attention to the burr. Its removal should be "occupied" by the bar with the finest grain. The burr is grinded on both sides in such a way as to give the cutting edge of the blade an angle of 23 - 45 °. It is this method of sharpening that allows the blade not to dull for quite a long time. The final finishing of the knife is carried out with slate and leather.

As you know, there are no universal knives. Based on this, the sharpening angle of each knife will depend on its purpose. For example, if it is supposed to be used only for slicing cheese, bread, sausages, and the worker - for enough soft materials(leather, paper, etc.), the sharpening angles of these tools can be minimized. If the knife is intended for cutting bony meat or other hard materials, then its sharpening angle should be approximately 30-45 °. It should be noted that the correct sharpening of knives at home for non-professionals can present some difficulties, therefore, it is recommended that novice "sharpeners" use a simple device for forming an edge under the right angle... For its manufacture, you will need from which you need to make a wedge. Its length should be 2.5 times its height. The resulting wedge-shaped device is installed on a touchstone, a knife is pressed against it from above, and then it is necessary to move a wedge with a knife along the blade forward. This method will automatically provide the required edge sharpening angle. In this case, a blade with a wide chamfer will receive a cutting edge at an angle of 25-30 °, and with a narrow one - 30-45 °.

Any knife made from the best steel or ceramics, dulls over time when working. This makes it difficult for the hostess to prepare food, increasing the time and effort spent, sometimes a dull knife slips and causes injury.

To avoid situations like this, you can use simple devices providing instant blade dressing for constant sharpness. Also, sharpening kitchen knives should be repeated periodically - this can be done at home using the simplest tools.

Having mastered the technique, you will not only please the hostess on March 8 and on other days, but you can also greatly surprise the guests (if there is nothing else) by demonstrating a knife at the table that can cut hair. This is precisely the degree of sharpness of a kitchen knife that can be achieved if you know how to properly sharpen a knife with simple inexpensive tools.

Sharpening the knife correctly is not the most difficult thing, the main thing is to listen to the recommendations

What knives can be sharpened

Can be sharpened kitchen knives of all types - first of all it depends on the equipment. Professional electric sharpening machines sharpen European, Japanese (one-sided), serrated (wavy surface), chopping, hunting, tourist, Ceramic knives with any sharpening angle.

You can effectively sharpen a knife at home if you have simple sharpening stones and follow the technology to the degree of hair cutting, which is more than enough when used in the kitchen.

Unfortunately, not all knives lend themselves well to sharpening.

Some types of knives are made by modern technologies with a coating of the cutting edge with a special wear-resistant compound that provides a self-sharpening effect. Sharpening kitchen knives of this type erases the special coating and the knife loses its advantages - of course, such models cannot be sharpened.

Blade sharpening angle

Knife sharpening angle - the deviation between the line of symmetry of the blade and the plane of its cutting edge.

The sharpness of the blade and its durability depend on this value: the smaller the sharpening angle, the sharper the blade, but it grinds down faster.

A larger knife sharpening angle reduces the sharpness of the cutting edge, but increases the duration of its work.

Kitchen types for everyday cutting of products have sharpening angles from 20 to 30 degrees, ultra-sharp medical scalpels sharpen at an angle of 10 - 17 degrees, hunting knives, kitchen household hatchets for chopping meat with bones and cleavers have a sharpening angle of 25 - 35 degrees.

To know at what angle to sharpen any knife, the blade is inserted into the scissors and the blades are compressed so that their tip is in close contact with the cutting edge of the knife. The angle at which the scissor blades will be pulled apart is the sharpening angle.

Musat

Musat is a device with a handle and a rod 20-25 cm long, reminiscent of a round or oval faceted file made of diamond-coated metal, hard steel or ceramics. The surface of the metal rod along the axis is covered with small grooves, the structure of ceramics is less relief.

Musat is used for regular daily lapping and grinding of the working edge of knives, allows you to maintain the sharpness of their cutting edges in a sharp state.

Musat is not suitable for all types of knives, only for models with a certain steel hardness

The main condition for the use of musat is the competent manufacture of cutting edges and the hardness of the knife steel is less than 60 units. Musat allows you to straighten out smoothing or bending of the cutting edge on hard surfaces.

Work rules

For inexperienced homeowners, sharpening on musat looks like this:

Musat is taken in left hand and rests with a sharp end on wooden surface at an angle of 25-30 degrees.
Knife in right hand moves from top to bottom in an arc towards the descent, the movements are repeated with little effort several times on each side of the blade.
On final stage finishing, the effort is reduced, after work, the musat is washed with water and hung for drying on the hook of the handle.

The generally accepted method of checking the quality of sharpening is to cut a sheet of paper - if you can draw curvy lines on it or cut off thin strips, then the sharpness of the blade is very high. The razor sharpness test can be done on the hairline of the hand - the sharpened blade cuts hair easily.

Sharpening stones

When deciding how to sharpen a knife, many primarily consider whetstones with varying degrees of abrasiveness. Modern bars have two sides - when used abrasive stones at the beginning, the side with a coarse-grained structure is used, at the end of sharpening, they move to the fine grain of the other side.

The sharpening stone is classic version for standard kitchen knives

Sharpening rules

Before and during work, the bars are moistened with water or soapy water - this is necessary to clean the pores of the bar from metal dust and its surface from the spent suspension, improve the sliding of the blade (many modern species do not require pretreatment with water). Knowing how to sharpen a kitchen knife will help the rules of work described in the instructions for the bar.

We moisten the stone with water, add a drop of dishwashing liquid on top.
We install the block on a flat surface, preferably with a slight relief (not a planed board) for better grip.
We apply the knife to the surface of the stone at the desired angle.

To set the angle, you can use a regular sheet of paper folded several times, in this case, you can get the final sharpening angle for the blade of 22.5 degrees (obtained by folding the sheet 90 degrees twice). We apply a sheet of paper with the obtained angle and a knife to the bar, we try to remember the resulting slope.

We install the knife at the beginning and across the bar, while the end of its handle should be at the very edge of the bar, and with a little effort, slide the blade along the bar in an arc in the direction of cutting. For a more stable fixation of the sharpening angle, you can support the blade with your other hand. The movement is repeated 40-50 times, then the side and direction of movement are changed.
If a burr edge appears along the entire length of the blade, stop sharpening on the coarse-grained side of the bar and switch to the fine-grain side. The sharpening operation is repeated, at the end the pressing force on the blade is reduced.
After processing the knife on a coarse-grained bar, it is possible to fine-tune it on musat.
At the end of the work, the bars are washed under running water.

If you wish, you can get razor sharpness knife. For this operation, genuine leather (a fragment of a leather belt) and an abrasive paste (GOI, Dialux) are used. The paste is applied to the belt and a knife is repeatedly passed over it at the desired angle, while the movement is opposite to the cutting direction.

Sandpaper

Sandpaper is the most economical option for keeping the knife sharp

The process of sharpening using sandpaper is no different from sharpening stones. You can even make an impromptu bar out of it by gluing or tying sandpaper To wooden beams: coarse-grained sandpaper is fixed on one side, fine sandpaper on the other.

Mechanical sharpener

Similar sharpeners, the most convenient way sharpen a knife at home

Standard design sharpeners mechanical type for kitchen knives is an oblong body, consisting of a handle for holding and several slots with sharpening discs for blades of varying degrees of sharpening. The sharpening angle when using it is constant and optimal for frequently used kitchen knives.

Another option for a manual mechanical sharpener is a roller knife, which has only one groove in the body for sharpening with mechanical rollers.

Sharpening set

The main task when sharpening and dressing knives is setting the exact angle. To accomplish this task, a wide range mechanical structures of grinding devices.

Some models consist of a base and a knife blade fastener, the sharpening stone is attached to the guide bar. When working, it moves along the blade at a set angle, then the knife turns over. The set is equipped with uneven-grain bars - this allows you to straighten the geometry of the blade and its polishing.

The sharpening set contains disassembled components for sharpening the knife. This set is quite compact.

Another type of a sharpening machine is a bed with a holder, into which sharpening stones are inserted vertically at an angle of sharpening, the knife moves in a strictly vertical plane sliding along the surface of the bar from top to bottom.

The designs of such devices are quite diverse and simple, everyone can make such a device from available tools with a minimum set necessary tools at home.

Electric sharpener

The fastest way to sharpen is with electric sharpeners for sharpening and polishing. Structurally, they are made in a closed case with a slot for inserting knives, inside there is an electric motor, on the axis of which conical abrasive wheels with diamond dusting are fixed. This method not very popular in everyday life due to the high cost of devices and is intended for professional work.

The electric sharpener will do all the work for you. You just have to hold the knife correctly at the right angle.

High-quality models of electric sharpeners usually have two types abrasive wheels- the first for restoring the geometry of the blade, the second for its final polishing, the sharpening angle in such devices can be adjusted or set automatically.

Some models electrical devices allow you to sharpen kitchen knives different types: European, serrated, Japanese, ceramic, and also scissors. In electric machines, each side has its own groove.

Work rules

With a very blunt working edge with serrations, the knife is processed on coarse-grained emery. It is inserted into the groove and stretches towards itself, the number of repetitions depends on the degree of dullness of the cutting edge.
After visual or contact checking for sharpness, the knife is inserted into the polishing groove and the process is repeated. To obtain a high sharpness of the blade, 5 to 10 broaches are usually required.

Grinder

The sharpening machine is professional option, with it you can sharpen a dozen knives in a short period of time

Many homeowners have a grinding machine at their disposal - electric motor with an abrasive grinding wheel mounted on a shaft, sometimes the machine has an adjustable rotation speed.

Abrasive wheels are often used to sharpen knives, but improper use (strong pressure and high speed) can easily overheat the steel and damage the blade. For sharpening on grinder you need to know the following rules.