If you own a knife, presumably you use it. If you use it, eventually it will become dull. This article is a guide to sharpening your blade on a whetstone or diamond stone.
Before you sharpen your knife, it is important to know the rough grind angle. This is the base angle used by the knife manufacturer to create the edge of your knife. Most knives have an angle between 10 and 30 degrees on either side, depending on the knife's intended use. The smaller the angle, the sharper the knife, and the more quickly the edge will wear. Razors have some of the smallest angle grinds, but they also dull the fastest. If you don't know the angle grind of your knife, you can usually find out this information by contacting the knife manufacturer or checking their website.
Most western knives have a double bevel, a grind on both sides of the blade. This means that the total angle of the blade is double the bevel grind on one side. Asian knives have a grind only on one side. This is why most Asian knives are so much sharper, and more delicate, than western knives.
Commercially available kitchen and general purpose knives generally have a grind angle of 22.5 degrees on each side. The 22.5 degree angle is important, because it's an angle that is somewhat easy to achieve by hand. To achieve this angle, simply go half of 90 to find 45, and then half again to find 22.5. The chart to the right illustrates approximately where these angles are.
Sharpening guides are probably the best way to ensure your blade has a consistent edge. Having an uncontrolled bevel angle is one of the biggest mistakes that are made when attempting to sharpen a knife. Most sharpening guides clamp on to the knife blade and hold it at a set angle against the abrasive surface. Rod guide systems hold the blade and then move the stone against the blade using the rod to keep the stone at a set angle. One of the drawbacks of most sharpening guides is that they cannot handle a curved blade. Rod guides overcome this problem by using a slender rod attached to a stone so that the stone can be moved in an arc to match the curve of the blade.
There are drawbacks to using a sharpening guide. Using a guide means that you lose some of the usable stone length. It also takes time to set a blade precisely in the guide, and it is difficult to set the blade exactly the same way and at the same depth in the guide every time. Many expert sharpeners avoid guides in favor of manually establishing the sharpening angle. Obviously this takes a steady hand and a lot of practice, but an experienced sharpener can create an extremely fine edge in this fashion. Experts who use this method often cite their ability to match the existing grind of a blade along a curved blade as the primary reason to manually establish the sharpening angle. Additionally, sharpening guides have a set angle, and if it is not the same as the blade grind, the result will be a blade with multiple bevel angles on its edge.
If you are a novice at sharpening blades, using a guide will help ensure that you obtain a consistent bevel angle. As you build your sharpening skills you can practice manually maintaining a bevel on old or bad knives.
Sharpening with a Whetstone
To sharpen a blade using a diamond plate or whetstone, first attach it to a sharpening guide with the proper angle. If you are sharpening the blade manually, without a sharpening guide, make sure that you have established the proper angle using a protractor or using the halving method mentioned above. As we mentioned above, many expert knife sharpeners go without any sort of blade guide and are able to precisely and consistently position the blade for a perfect grind.
There are three strokes you can use when sharpening a blade on a stone: circular strokes, drawing the blade away from the edge, and drawing the blade towards the edge. Drawing the blade away from the edge is a good initial stroke that is used on coarse- or medium-grit surfaces. Moving the blade in this way allows burs to form on the edge of the blade (which we will remove later) and ensures that neither the stone nor the blade is damaged by the blade edge trying to cut into the surface.
Burrs are developed when enough metal is removed to meet the bevel on the other side of the blade. By feeling the edge of the blade opposite of the side you have been grinding you can tell if you have burrs beginning to develop or not. If the edge is smooth, continue grinding; no burrs have begun to form yet indicating that the opposite bevel has not been reached. If you can feel the burrs (they feel rough to the skin, but you can't see them) then you are ready to proceed to grinding the other side of the blade. When both sides of the blades have been ground proceed to a finer grit. To draw the blade away from the edge, position the blade on the stone so that the blade is facing away from you and draw it towards you across the stone.
To begin sharpening your blade, first lubricate the stone with a thin film of water or oil depending on the stone type. Then set the blade or the sharpening guide on the stone. For an initial coarse grind, a water stone with a coarse grit between 180 and 300 is a good place to start. On this grind, use a stoke that draws the blade away from the edge. A coarse grind should only be necessary for the first grind on a new blade or to repair a nicked or damaged blade.
After establishing a rough edge, move to a medium-grit stone (360 to 500 grit) and continue sharpening by drawing the blade away from the edge or by using circular strokes. A medium-grit stone is where you will begin sharpening a blade that already has an edge on it that has become dulled from use.
Finish sharpening on a fine-grit stone with a stroke that draws the blade towards the edge (the opposite from the stroke on the medium or coarse stones). To draw the blade away from the edge hold the blade on the stone at the correct angle with the blade edge facing towards you, and pull the blade along the stone to you. Alternate sides with each stroke. This prevents additional burrs from forming on the edge of the blade.
After using a fine-grit stone the blade can be further polished on a strop or felt wheel. (See our article Honing and Polishing A Blade for details on finishing a blade in this fashion.) Polishing the blade in this fashion removes the microscopic serrations left by the grit of the whetstone or diamond stone. This enhances the push cutting ability of the knife (pushing straight down onto an object rather than slicing across it) but does so at the expense of the blade's slicing ability. Without the microscopic serrations the blade will not bite into the surface that is being cut.
When testing a blade to see if it is sharp, don't drag your finger across the blade. A better test is to hold a loose piece of paper in your hand and try to cut it with the blade.
Sharpening with a whetstone is the oldest method of maintaining a blade edge. Some expert sharpeners say that this "stone age" technique should be relegated to museums, but it's one of the cheapest and easiest methods to refinish a blade. The satisfaction of being able to pull out a pocket stone and manually hold an angle while touching up a blade is hard to beat. You don't need fancy sharpening systems or kits, and you don't need expensive grinding machines or polishing wheels. With just a couple of stones and a bit of mineral oil or water you can maintain all of your blades for a lifetime of use.