The performance of a knife as a cutting tool is determined by many factors. While the most obvious—blade steel and heat treatment—do have a profound impact on cutting performance, the grind of the blade is equally important. And when it comes to choosing a knife that is appropriate to your needs and style of knife use, understanding blade grinds and the edge geometry they provide is critically important.
The grind of a blade is basically the shape of its cross-sectional profile—what you would see if you cut a blade in half and looked closely at the cut end. This profile is created by the grinding process that produces the primary blade bevels and is determined by shape of the grinding media and the mechanics of that process.
In simple terms, there are three basic types of primary blade bevels: flat (a perfectly flat plane), concave (curving inward), or convex (curving outward). They can also extend the full width of the blade or only part of its width, leaving the spine of the blade full thickness for maximum strength. In most cases, the primary blade bevels intersect with a set of secondary bevels that form the blade’s actual cutting edge; however, some grinds—such as the Scandinavian or “Scandi” grind—the primary bevels actually intersect to form the cutting edge. This style of blade is often referred to as having a “zero ground” edge.
Blade bevels are critically important to the cutting performance of a knife because they determine the amount of resistance a blade experiences while passing through a material. Think of a knife blade as a wedge. Thin wedges separate materials gradually and typically offer less resistance. Because they are thin, they are also weaker. Thick wedges split materials quickly, but meet greater resistance as they do. They also offer greater structural strength. Optimal blade geometry is therefore a matter of balancing the resistance experienced while cutting with the strength of the blade relative to the tasks being performed by that knife.
Since most blades have secondary bevels to create the actual cutting edge, one other important—but often overlooked—aspect of blade geometry is the terminal thickness of the primary bevels. In other words, how thick is the blade where it transitions from the primary bevel to the secondary bevel of the actual cutting edge. While a thicker blade will offer greater strength, it also creates an abrupt transition from the cutting edge to the primary bevel, increasing resistance. Increased thickness at this point also requires that the secondary bevels of the cutting edge are wider and can shorten the useful life of the knife over repeated sharpening.
The three most common blade grinds used by Spyderco are the following:
Saber Grind: This is a partial flat grind. The upper half of the blade is left full thickness for strength, and the primary blade bevels are ground flat on the lower half. Secondary edge bevels create the actual cutting edge. This style of grind offers maximum strength, but the trade-off is increased resistance during cutting. Saber grinds also cannot be sharpened as many times as other blade geometries.
Full-Flat Grind: As its name implies, a full-flat grind features flat primary bevels that extend the full width of the blade. Again, secondary edge bevels create the actual cutting edge. The wide, flat bevels of this grind greatly reduce friction and allow full-flat-ground knives to excel at slicing chores. That’s why this grind is typically used on kitchen knives. Full-flat-ground blades are also lighter than saber-ground ones, but do not offer the same strength.
Hollow Grind: A hollow grind is produced by using round grinding wheels to create concave blade bevels. Spyderco knives typically use a partial hollow grind, which leaves the upper half of the blade at full thickness for strength. While seemingly similar to a saber grind, the concave shape of a hollow grind reduces the terminal thickness of the primary bevels, easing the transition from the cutting edge to the bevel and reducing friction. Hollow-ground blades also have a longer sharpening lifespan than saber-ground blades.
Originally appeared in the June 2014 Spyderco byte e-Newsletter.
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