Story and Photos by Michael Janich
When most people think of knife design and the effect it has on its function as a weapon, 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 strength of the knife’s tip and the ease with which the blade penetrates during a thrust. However, when it comes to personal-defense knives, I would argue that the profile of the cutting edge is the key determining factor in quantifying the destructive power of the blade.
Self-defense knives are limited by carry laws.
While 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 typical 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 actual length into flesh. If the blade’s 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 are certainly targets on the human body that can prove lethal when punctured to a depth of three inches, only a small fraction of them offer the possibility of a quick “stop” that will eliminate the threat and keep you safe. More importantly, hitting these precise targets in the middle of a lethal-force struggle is extremely difficult.
However, cutting tactics can be effectively applied to many targets that produce predictable, immediately disabling, effects. The depth of cut necessary for these tactics is typically much less than three inches and, in some cases, less than an inch. These targets are also larger and much easier to access in a violent struggle than the preferred thrusting targets.
The trick to exploiting them most effectively – with a legal-sized blade – is understanding edge profiles.
The human body is designed to move in arcs. Our joints are hinges, or ball-and-socket structures, that move our limbs in curved paths.
Click on images for details.
While true straight-line thrusts are possible with sufficient training, most tactics – especially cuts – move in arcs. A cut with a knife traces the same basic trajectory as the hand wielding it, with the cutting edge of the blade creating a swath at the outer radius of that arc.
More specifically, the tip of the blade defines the outermost radius of that arc. The destructive capacity of a cutting edge is therefore determined by its ability to cut with its full length while applying firm, consistent pressure into the target.
Let’s take a look at some of the prominent self-defense profiles and weigh the pros and cons.
Hawkbills and Karambits
Based on these dynamics, hawkbill and karambit blades typically achieve first contact with the point.
Like an animal’s claw, they pierce as they cut, with the blade tip clearly defining the depth of the cut. If the initial penetration is far enough forward into the target, the rest of the edge will continue to cut as the point penetrates, until the heel of the blade reaches the target.
However, if the tip hits bone before the full depth of the cut is reached or you initiate the cut with the heel of the edge, the blade snags and the cutting action stops.
Trailing Points and Tantos
Trailing-point blade profiles, with lots of “belly,” are often touted for offering more edge for a given length of blade. While this may be technically true, the fact that the edge curves upward actually limits its cutting efficiency.
The reason for this is that as the edge nears the point, the pressure it applies into the target decreases significantly as the radius of the edge runs parallel to the arc of motion of the hand. The angle of that pressure also tends to push the target away, further minimizing the depth of the cut.
The limited cutting pressure offered by trailing point blades is exactly why they are preferred for skinning and caping knives. When you don’t want to cut too deeply, the belly of the edge allows a very precise, purposely limited, depth of cut.
Tanto-style blades – specifically, the Americanized tantos that most people associate with this term – perform the exact same way as trailing-point blades. Because their edges sweep upward near the tip, they cut with power from the heel of the edge to the transitional angle of the edge. At that point, the pressure the blade applies into the target drops off dramatically and the cutting action stops.
A perfectly straight edge cuts with the same pressure along its entire length. That’s why this style of edge is used on the utility razor knives – used in trade and hobby work. In folding knives, the straight edge is usually combined with a gently curved or faceted spine – like half a trapezoid.
Although sometimes mistakenly referred to as a “reverse tanto,” this blade style is more properly called a Wharncliffe, after the 19th-century Englishman Colonel James Archibald Stuart-Wortley-Mackenzie – the first Lord Wharncliffe of England – who designed it for production by the Joseph Rodgers & Sons cutlery company in Sheffield.
The tapered spine and straight cutting edge of a Wharncliffe also yield an exceptionally acute point. While this reduces the strength of the blade’s tip, it also increases its penetration on a thrust. As the blade penetrates, the ramp on the back of the blade pushes the cutting edge downward, shearing along its length to open the wound channel.
Upon full penetration, additional pressure on the edge will extend the wound channel its full depth. If it strikes bone, the edge literally circumscribes its circumference, cutting to the maximum possible depth without snagging.
The combined dynamics of this thrust/cut action – called a “Comma Cut” in the Martial Blade Concepts system of knife tactics – truly maximize the effectiveness of the Wharncliffe and demonstrate the full potential of a small defensive blade.
If you carry a knife for personal defense, don’t just carry a knife; carry the most capable knife you can. One key to doing that is understanding your blade’s edge profile and its true destructive capacity.
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Martial Blade Conceptswww.MartialBladeConcepts.com
Nine-year veteran of the U.S. Army Intelligence and Security Command, Michael Janich also served a 3-year tour at the National Security Agency. Highly decorated, Michael is a two-time graduate of the Defense Language Institute and served around the world in intelligence and investigative capacities for many years. Utilizing his extensive training in various martial arts and military/LE combatives, he established Paladin Press’ Video Production Department in 1994, running all aspects of video production for 10 years – personally recruiting some of Paladin’s most popular authors and being selected to work with the late Col. Rex Applegate as the producer of his landmark instructional videos on handgun point shooting. Published book and magazine author, Michael has been featured on various television programs and designed knives for many different knife companies throughout the industry. Michael is the founder and lead instructor of his signature knife defense program, Martial Blade Concepts.
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