There are many devices out on the market that are designed for sharpening knives, through mechanical ways. There are many types of these things, but though they may be as effective as using a stone, they are not at all better than using a plain old water or oil stone. Here are two main types of these devices, and I will explain why they are inferior to a stone.
A sharpening jig is a device where the knife is clamped into the jig at a certain angle, and the whole thing is run over a stone. These are fairly common and popular with the general sharpening population. There are two main problems with this, and are present with most sharpening devices. First, and the most technical, is that the jig focus’ mainly on the primary edge of the knife, and grinds away only that, not the secondary edge (also known as the “grind”). This does not do much in the short run, but in the long run, every sharpening of the primary edge grinds a little further away from the edge, and so gradually, the blade gets smaller and smaller. If the whole blade is not thinned a little every time it is sharpened, then gradually the angle of the edge gets steeper and steeper, and this seriously effects the overall cutting. The second of a Jig’s problems, is not really a big problem for someone who wants to just occasionally give it an edge. This problem, is that you do not get the experience with a jig that you would get with just a regular stone. With just a stone, your hands get the feel of how much the stone grabs the metal, how much the metal will bend, etc., and just gives you an overall feel for the knife and it’s properties.
This is a mechanical device, where you flip a little switch and the small grindstones start spinning, and all you do is draw the edge of the knife in between the little wheels, and it grinds away a bit of metal and sharpens the knife. This has the same two problems as the jig, but with an extra one thrown in. The wheels, when they grind away at the edge, make it concave, which wears away VERY quickly when the knife is put to use.