You have probably already been upset about a dull knife in your kitchen. You may also know that a dull knife is potentially more dangerous than a sharp one. A greater force has to be applied when using a blunt knife. If its blade reaches an unwanted place, it may do big harm.
We will try to explain quickly and easily in the following text, how to sharpen a knife without special grinding machine in your own household.
Prepare an oiled or with water soaked stone. We suggest to let the stone soak for 5 minutes in water before use. You will get exact information in instructions brochure delivered with your whetstone.
We do not describe here how to grind a knife with modern knife sharpeners that sharpens with steel. This way of sharpening may generate heat. Excessive heating can temper microscopic layers of steel and change the crystalline structure. The steel is then softer and will wear out quickly (i.e. becomes dull). Moreover, the cutting edge is ground only at one angle. Various knives are sharpened at different angles (15-45 °). However, for grinding in emergency cases they are good.
The original cut should be in good condition if you want to get a good result. The left image shows an edge that can be sharpened this way.
The right picture shows a too dull cut. Such a blade should be left to a professional.
The following picture shows profiles of industrially manufactured blades, the edges of which are ground at more obtuse angles than the rest of blade. This profile prevents accidental breaking out of the blade edge.
Knives can be well sharpened by laymen, but special attention should be paid to a constant angle of the cut/edge. An angle clamp can help you a lot. Modern sets of knife sharpeners have multiple angle clamps for different angles of edges.
The further instructions are written for right-handed. If you're left-handed, it's vice versa.
Place the blade with proper angle on the (from you) farther end of the grinding stone and drag the knife gently to yourself slightly to the right. The blade edge is pointing to you. Drag the blade at constant speed and angle to the stone surface.
Each grinding drag ends when the blade tip reaches the other end of the stone. Be careful that you do not pull over the stone verge. Grind as if you wanted to cut a thin slice from the stone surface.
This way you can grind the blade several times and check the cutting edge from time to time. Do not forget to sharpen the other side of the blade (only applies to blade with double-sided cut) so that the blade is symmetrical.
The grinding angle usually amounts to 15-20° at filleting knives, 25-28° at hunting knives and 35-40° knives for woodworking.
The sharpness depends on the used steel of the blade (its material structure) and on its hardness (specified in degrees Rockwell). The steel for utility knife has max. 62-64° Rockwell.
Knives with steel hardness of 53° have a good cutting performance and are easy to sharpen, but their edge is not very durable.
The resistance is related to steel hardness. The harder the material, the longer remains the cutting edge sharp. But its grinding requires more moves. Here you have to decide if you want to sharpen knives easier or prefer a more durable cutting edge.
We can find a sharpening steel probably in every household. It is well suited for fine-grinding, after the knife has been sharpened with a whetstone, as described above. A precision grinding with sharpening steel is not easy because you have to pay attention to the angle of the edge.
It is important to note here that the sharpening steel is suitable just for maintenance of the edge. A very blunt or jagged blade cannot be sharpened with sharpening steel!
Before you get to the right sharpening with sharpening steel, you should train with a cheap knife and then reach for a more valuable knife. You can support the sharpening steel against the table top, as shown in the video below. Remember to keep the grinding angle and to grind from both sides.