In this series of articles we are going to put forward what like to term “Critical Design Elements” of Defensive knife design, that is knives which are purposefully designed to be carried and accessed from a concealed position, during or just prior to a Close Combat Incident (CCI) which has potentially lethal outcomes.
This is an important definition because it sets the parameters of how the knife will be used and the conditions it has to be used in. Many of the knives at Ironside Edge Works were designed by its founder Gavin Coleman, who also happens to be a co-author of “The Maul: Preparing for the Chaos of Close Combatives“. A book widely regarded in the world of edge and point application, and combatives in general. So we like to think our work in this particular niche of knifemaking is well supported and comes from a solid foundation. This type of information is aimed at both knifemakers who want to get into making defensive knives, as well as those buying and carrying them.
In this first article we will talk about the blade itself.
Whenever you are designing a blade it’s important to fully understand the job it is going to do. This will heavily influence your design. It would be silly to put a hairline razor edge on an axe for example, knowing that it is going to be used to chop heavy and dense materials. So first we need to really understand the function of a defensive knife, and what type of materials and stresses the blade is likely to encounter doing its job.
First let’s understand what kind of damage we would want the knife to do. To put this as bluntly as we can we want our knife to be able to deliver damage to a human opponent. This damage may be lethal, biomechanical or superficial, but our primary target materials are organic. Flesh, tendon and bone. It’s important to also understand that lethal damage on a human target requires depth. To reach organs and a lot of the higher volume blood vessels will require the blade to penetrate 2” – 3” depending on the physiology of the opponent and the exact target. The take away from this is understanding that lethal damage is found at depth and is primarily achieved by stabbing – not cutting or slashing. We need our blade to be long enough to reach what it needs to damage, but not so long that it becomes cumbersome and difficult to access or work with in an entanglement.
The second understanding you must have is just exactly what lethal damage looks like from an knife. There are very few specific targets on a human body that will be lethal immediately, and even fewer which can be readily accessed by a knife blade. The ones which are require a knife blade that can deal with hitting bone. The heart is encased in the rib cage. Rib bones can be avoided if you are lucky and/or very skilled, but there is a better than average chance you will hit the rib bones in an actual, un choreographed real life CCI (Close Combative Encounter). Another instantly (within reason) lethal target is the central nervous system (CNS) accessed between vertebrae in the neck. This again would require the blade to penetrate between boney structures which are designed to protect the very thing you’re trying to damage. What does this mean? The blade needs to withstand hitting bone, and not just delicately, it needs to withstand it at force because an adrenaline fuelled CCI is not a delicate thing. Knives also just get stuck in bone. If the tip of the blade does get stuck it is now at risk of snapping from lateral torque. This is why you are always told never to pry with the tip of your blade, lateral torque breaks tips. So to get around this the blade tip needs to be structurally robust enough to negate the effect of this. Hopefully when (not if) your blade gets trapped in bone or in the joint, any lateral torque that develops as a natural result of the fight (grappling, twisting, pulling, falling, etc.) will transfer into the bone, breaking it and not your blade.
Of course you also have other options, there are plenty of places to put the blade which will result in soft tissue damage that can eventually become lethal, but these require time and a good understanding of the situation. Soft tissue damage can be amplified by the edge as it cleaves through tendon, blood vessels and muscle. To do this the edge doesn’t need to be a razor. Again we aren’t talking about delicately push cutting a piece of paper with minimal effort here – this is a fight fuelled by adrenaline and you are likely to be plunging your weapon into your opponent with force.
So ideally you want an edge that will cut but also be robust enough to deal with hitting harder materials without chipping or rolling. Again this means structurally supporting the edge, just like the tip, with enough material to ensure that damage doesn’t occur.
We can also consider for a moment the secondary materials which may come into play. Your opponent is likely to be clothed. Heavy garments like jackets and hoodies can be exceptionally good at protecting against cutting (which again is why stabbing should be the primary function) and even a cotton t-shirt can get tangled up in a blade. Heavier fabrics, materials like leather and even metal zippers and buttons all need to be considered as potential materials the blade will interact with and need to survive.
So how do we achieve this toughness?
We make the point of our knife strong enough to withstand the abuse. This can be achieved in a lot of ways, through geometry, and the thickness of the steel, but also the steel itself. Some are tougher because of their metallurgy. Using an inherently tough steel is a good idea. This is why we prefer 80Crv2 as it offers the good balance between toughness and hardness, allowing us to create a sharp edge but a tough driving point. Knife and blade making is always a trade off. We trade one positive trait for another. Want more toughness? You’re going to sacrifice sharpness. Want sharpness? You’ll get less toughness. Sometimes you can balance both relatively equally, which is what we believe is the best option for defensive knife design.
We aren’t so naive that we believe only the best knife in the world can do lethal damage. It’s often been said that most assaults are carried out with cheap disposable knives. Which is true. Almost any knife has the capacity to be lethal, but there are other considerations.
Chiefly it’s context. As a criminal actor you have a tremendous advantage of being the one who chooses the time and place and target of your assault. You have the advantage of surprise and preparedness. You likely have the weapon drawn, perhaps even taped to your hand, and are willing to dispose of it. Even if it breaks mid assault, you have the prerogative to being able to cut and run. For them, failure means trying again another day, for you however failure means death. This is why are advocate stacking the odds in your favour, as much as possible. Even if you only gain a 1% advantage, it’s odds that are slightly better. This is why every thing matters.
Next we will talk about the second critical design element of Defensive knife design. Ergonomics.