In addition to the nature of the sharpening tool, the angle at which the cutting edge strikes the abrasive is crucial for the sharpening result. Although there are tables, in most cases a sense of proportion and skill are essential. There is a relatively simple trick to checking the correct angle when sharpening.
Two bevels make two angles
Before sharpening a knife, take a close look at the existing grind. Most blade edges have two grinding graduations when viewed from the blade face. A wider bevel starts about halfway down the blade face and runs at a very shallow angle toward the “bending” second bevel, the actual cutting edge.
In technical terminology, the wider upper bevel is called the primary bevel. The cutting edge emerges from the secondary chamfer. The final piece leads into the micro bevel, which in turn can have an increase in the angular value, but does not have to. Here, the reduction or elimination of the burr plays the decisive role.
Blade grinding types and bevel ratio
Another important aspect in order to perform sharpening and machining at the optimum angle is the shape of the blade grind. There are five types of grind that create what is known as blade geometry:
- Flat grind
- Hollow grind
- Crowned cut
- Scandinavian cut
- One-sided cut
With the different types of grinding, the proportions of the primary and secondary bevels change. With the flat grind, the primary bevel “kinks” just before the blade edge. This gives the secondary bevel a higher angle.
The bevel ratio in hollow grinding is similar, but the primary bevel is “indented” towards the inside. This results in a lighter cutting force due to lower displacement mass in the material being cut.
In the crowned or convex grind, the bulbous primary bevel transitions smoothly into the secondary bevel. The angle changes smoothly according to the rounding.
The Scandinavian grind also has only one bevel, which runs straight toward the cutting edge along a short path on the blade face about one-third of the blade width.
The one-sided bevel represents half of a flat bevel. The two bevels are ground in the same way and the back of the blade remains unsharpened. This grind is rarely used on utility knives in the home and is most commonly found on planer knives.
A simple control trick
The challenge in sharpening is to match the sharpened surface with the machined bevel. Figuratively speaking, the imaginary line of slope of the existing grind must be extended. Of course, the actual sharpening, if any, takes place in the angular dimension of the secondary bevel.
To check the angle, the secondary bevel of a flat or hollow grind is evenly colored with a dark abrasion-resistant felt-tip pen. In the Scandinavian grind, the entire bevel is marked. When the blade is dragged across the grindstone, the color removal indicates the correct or incorrect grinding angle. If the grinding angle is too shallow, paint residue will remain on the cutting edge; if the grinding angle is too steep, paint residue will remain on the bevel side towards the center of the blade.
Tips & tricks
You should always use a magnifying glass with 80 to 200 times magnification to check your work, which also allows you to easily see the different angles of the bevels.
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Elizabeth Green
Elizabeth Green is a seasoned home chef and culinary expert who has a passion for all things kitchen-related. With her extensive knowledge of the latest kitchen products and appliances, Elizabeth provides insightful reviews and recommendations to help consumers make informed purchasing decisions. Whether you're looking for a new refrigerator, blender, or cookware set, Elizabeth is your guide to finding the best kitchen products available in the UK.
