Edge profile—the actual shape of your blade’s cutting edge—has a tremendous effect on its performance as a defensive weapon. You need to understand how to get the most cut out of the blade you carry.
A typical knife with a “belly” to the edge. The arc on the right, which meets the edge’s straight section at a right angle, represents the blade’s and hand’s arc of motion during a cut. The line along the edge represents the pressure that the edge applies into the target. As you can see, the pressure remains constant (or even increases) along the edge’s straight section. As the edge curves upward, the pressure diminishes quickly as the edge’s arc and the hand’s arc of motion approach parallel paths. Less pressure means a shallower cut.
When most people think of blade design and its effect on a combat knife’s functionality, they typically focus on blade length and point profile. Blade length obviously has a direct bearing on the depth of the targets you can reach, while point profile determines the point’s strength and the ease with which the blade penetrates during a thrust. However, when it comes to self-defense knives, I would argue that the cutting edge’s profile is the key determining factor in quantifying the blade’s destructive power.
Self-defense knives are limited by carry laws. And while I know that some jurisdictions do allow the carry of potent, combat-style knives, most states and municipalities restrict knife carry to folding knives with reasonably short single-edged blades. Rather than arguing the exceptions, let’s focus on the rule and consider how blade shape and edge profile affect the performance of a legal-almost-everywhere 3-inch single-edged blade.
First of all, let’s address penetration. Since tissue can compress, a 3-inch blade can actually penetrate slightly more than its length into flesh. As long as the point is reasonably sharp and your attacker is wearing reasonably normal clothing, achieving full penetration of the blade during a thrust isn’t difficult. Unfortunately, it also doesn’t guarantee a fight-stopping wound—especially against a large-framed attacker. The simple truth is that while there certainly are targets on the human body that can prove lethal when punctured to a 3-inch depth, only a small fraction of them offer the possibility of a quick “stop” that will eliminate the threat and keep you safe.
Conversely, cutting tactics can be effectively applied to a variety of targets that can produce predictable, immediately disabling effects. The depth of cut necessary for these tactics is typically less than 3 inches and in some cases less than an inch. These targets also are larger and much easier to access in a violent struggle than the preferred thrusting targets. And the trick to exploiting them most effectively with a legal-sized blade is understanding edge profiles.
When most people think of blade design and its effect on a combat knife’s functionality,…
by Terrill Hoffman / Jul 23, 2013