Knife sharpening is a great skill to acquire, and will endear you to most cooks who often have to put up with blunt knives. Knives are sharpened by grinding against a hard rough surface, typically stone, or a soft surface with hard particles, such as sandpaper. For finer sharpening, a leather razor strop, or strop, is often used. The smaller the angle between the blade and stone, the sharper the knife will be, but the less side force is needed to bend the edge over or chip it off.
The angle between the blade and the stone is the edge angle the angle from the vertical to one of the knife edges, and equals the angle at which the blade is held. The total angle from one side to the other is called the included angle on a symmetric double-ground edge (a wedge shape), the angle from one edge to the other is thus twice the edge angle.
Very sharp knives sharpen at about 10 degrees (which for a double-ground edge implies that the included angle is a 20-degree angle). Typical knives are sharpened at 20 degrees. Knives that require a tough edge (such as those that chop) sharpen at 25 degrees or more.
The idea is to cut an even beveled surface along either side of the blade at an acute angle, about 20 to 25 degrees. Where these two bevels intersect the knife edge is formed. The bevel should be about 1mm (1/25in) wide. Stroking a knife blade across a stone at a constant angle and direction will produce a fine barbed edge. This process is called “honing”. The effect can be seen under a microscope, but a bit difficult with the naked eye.
Knife sharpening by stroking a knife blade from heel to tip will impart an edge that cuts the best when the blade is pushed. Stroking from tip to heel sharpens the edge to best cut when the blade is drawn. When knife sharpening, never change the stroke direction, once begun.
The hair fine scratch lines across the edge of the blade should be in one direction, parallel at about 45 degrees to the edge. Each scratch mark produces a minute barb where it runs to the edge of the knife blade. The finer these barbs are, the longer the knife will stay sharp.
We offer here a few free PDF file downloads that might assist you in your quest in knife sharpening.
1. How To Sharpen – Behr/Manning published 1955
2. Knife Sharpening Basics – for Japanese hard steeled knives (these blades can be forged with a hard steel center cutting edge encased on either side by softer iron).
3. Sharpening and Maintenance of Knife Edges – from the book Buckskin.