Knife Sharpening

Knife sharpening is a great skill to acquire and will endear you to most cooks. They often have to put up with blunt knives. Sharpen a knife by grinding against a hard rough surface. Typically this is a stone or a soft surface with hard particles, such as sandpaper. For finer sharpening, use a leather razor strop. Additionally, the smaller the angle between the blade and the stone, the sharper the knife will be. But less side force is needed to bend the edge over or chip it off.

The angle

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 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 (a double-ground edge implies that the included angle is a 20-degree angle). So twenty degrees is the angle to sharpen most knives. Blades that require a tough edge (such as those that chop) sharpen at 25 degrees or more.

The idea is to cut an even bevelled surface along either side of the blade at an acute angle, about 20 to 25 degrees. So the intersection of these bevels forms the knife edge. The bevel should be about 1mm (1/25in) wide. Therefore, stroking a knife blade across a stone at a constant angle and direction will produce a fine barbed edge. This stroking is “honing” a knife. It is a bit difficult to see this edge with the naked eye.

Stroking a blade from heel to tip imparts an edge that cuts the best when the blade is pushed. Stroking from tip to heel sharpens the edge to cut best when the blade is drawn. Additionally, when knife sharpening, never change the stroke direction once begun.

The hair’s fine scratch lines across the blade’s edge should be in one direction, parallel at about 45 degrees to the edge. Each scratch mark produces a minute barb running to the knife blade’s edge. The finer these barbs are, the longer the knife will stay sharp.

Knife Sharpening Resources

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 centre cutting edge encased on either side by softer iron).

3. Sharpening and Maintenance of Knife Edges – from the book Buckskin.