Functional Knife / Sword Design

Functional Knife / Sword Design

BY : Web Admin

This article is based on a lecture I gave at the New England Bladesmiths Guild Ashokan Seminar in 2013.  It was originally focused on sword design but it also applies to functional knife design. I was originally a custom bladesmith and began making knives according to the contemporary literature and examples of American custom knife makers that I met at the knife shows. As I made and tested knives of contemporary American designs I was surprised to find that they didn’t really perform that well, handles were uncomfortable after moderate use and the blades didn’t really cut that well (compromised blade geometry). It wasn’t until I started studying historical and ethnographic knives/swords that I began to understand functional design. Ethnographic knives/swords were readily available at gun shows and were designed for a variety of functions including cutting, chopping, stabbing, etc.  They were also very affordable and I could purchase them and bring them back to my shop for study and testing (this was during the mid-1980s). They were edged tools used by people who depended on them for everyday use and they needed to work well and for long periods of time.  After all, what we call “bushcraft” today was normal day to day life for peoples all over the world and throughout most of our history. This has since changed with modern technology and powered cutting tools and our reliance and expertise with hand powered cutting tools has dwindled.


Since my personal focus has always been functional knife/sword design I decided that I should study knives/swords from the perspective of  “Bladed Hand Tools”. Knives/swords fulfill many roles and a functional role is only one of them. Throughout history they have also been status markers, jewelry, indicators of social groups/rank/occupation, neat things that people wanted, etc. What follows is a breakdown of each aspect of functional design some of which may appear obvious and simplistic but are nevertheless important.




The first aspect of Bladed Hand Tools that I would like to discuss is knives as tools and what that entails.


  1. Knives/Swords are functional tools not simply objects.


  1. Function of a Tool- tools are defined by what they do, not what they look like. Sal Glesser used to say when you buy a drill you don’t really want a drill what you really you want is a hole.


  1. Implied Aspects of a Tool
                      a) Performance- the tool performs it’s job well.
                      b) Longevity- a tool is acquired with implied long term use. It should use appropriate materials and heat treatment for the tasks for which it is designed.


  1. Five Dimensions of Bladed Hand Tools


  1. Length
  2. Width Blade Geometry
  3. Thickness/Tapers
  4. Material and Heat Treatment- Depending on the application: for example- stainless steel for knives exposed to a wet or corrosive environment, carbon steels for heavy duty cutting/chopping. Higher hardness microstructures for lighter cutting and thin edges, lower hardness microstructures for heavy duty applications. It is also important to determine the best microstructure for the designed task by physical and metallurgical testing.
  5. T & T
                   a) Target- media to be worked. From vegetables and meat to wood, rope and cardboard. What is being cut is a critical factor to be taken into consideration when determining the geometry, material and heat treatment of the blade.
                  b) Technique- cutting, carving, slicing, skinning, stabbing, food preparation, etc. These aspects need to be considered when designing both the hilt and blade of a knife.


  1. Two Critical Transitions and Interfaces


  1. Transitions
                    a) Blade to Tang- tang supports blade function.
                                    1) Heat Treatment- the first inch or so of the tang must be heat treated so it is as strong and flexible as the blade.  I have seen commercially made knives which are only heat treated to the blade shoulder and these bend easily when lateral force is applied.
                                    2) Configuration- tangs should be as wide as possible at the transition for strength and the blade shoulders should have as large a radius as possible. I have seen blades breaking at this point if the radius is too small especially with laser cut blades.
                   b) Blade to Edge- blade as edge support/edge delivery system. This is one of the many examples in blade design where the dimensions/materials/heat treatment must be pushed to the limit of failure. The blade should be thin enough at this transition to provide a smooth flow in the cut but be thick enough keep the edge from failing.


  1. Interfaces
                  a) Hand to Hilt- the tool is unusable if this interface is unsuitable. Material, profile and cross section of the hilt must be designed to be comfortable in the hand and be suited function of the knife.
                   b) Edge to Target- edge must be suitably designed and constructed for target media. Depending on the media to be worked the edge can be more or less acute and smooth, polished or rough. This is probably the most critical of interfaces for performance and every aspect of the knife design culminates in this interface.







  1. Hilt Must Interface Comfortably With Hand- no sharp edges, “hotspots”, wear spots, etc. Must be able to be used for extended periods.
                 a) Communication- hilt must convey pertinent information to the hand. Critically important is edge alignment, the hilt should let the hand know where the edge is at all times.
                b) Stability- the hilt should be designed to keep it in the hand when being used. For example-heavy duty chopping knives often feature an element to keep the knife in hand at the end of the swing like a bird’s beak.
               c) Range of Movements- the shape of hilt defines the range of motion available to hand. The hand is quite adaptable and should be able to move freely on the hilt. For example, finger grooves and sub-hilts severely restrict hand movement and limit the versatility of the knife.
              d) Protection- the hilt should protect the hand from the blade. A guard or other features of the hilt (single finger groove, extended ricasso, etc) should be considered to keep the hand from sliding forward and contacting the blade.


  1. Force- the hand/arm defines how much force is available to drive the tool. Longer/heavier blades can create their own momentum, shorter blades driven by hand/arm force alone.




         Blades are subtle things- very small design changes can lead to large differences in performance


“Geometry determines how a blade cuts, steel and heat treatment determine how long a blade cuts”- Roman Landes


  1. Blade Cross-Section- thin cuts, thick strengthens
               a) Cutting knife- thin blade tapers to support a thin edge. Cross section of the blade must minimize resistance in the cut.
               b) Strong- thick blade and/or variable saber grind. In the second generation of the SP Gen IIs I had the blades (with the same profile) both flat and saber ground. The difference in handing and performance characteristics was remarkable. The saber ground blades, even the shorter models, would chop very effectively and the flat ground blades would cut very well.


  1. Blade Profile
              a) Wide- most effective profile for cutting/slicing knives especially when combined with a back to edge taper grind.
              b) Narrow- most effective profile for rotational/complex cuts. Good examples are boning and fillet knives where the blade has to cut closely along the surface of the bone/spine.


  1. Edge- edge works by concentration of force on a very small area. Thin, strong edges depend on an exceptionally strong material such as heat-treated steel.




         For functional bladed hand tool design:


  1. Define what you need the Bladed Hand Tool to do- what is the task it is designed to perform.


  1. Experiment and Test for Five Dimensions and Critical Transitions and Interfaces


  1. Select a proper material and heat treatment to perform the designated task and to insure longevity.


  1. Pay particular attention to blade geometries and experiment and test.


  1. Testing- take Bladed Hand Tool our and use it.

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