Edge Geometry

Heat treatment is said to be the defining characteristic in a physically well-performing blade. This is only half true. A soft blade will lose its edge quickly, a hard one is more likely to break. So yes, heat treatment is essential in the long run. However when it comes to immediate cutting performance, what really hangs in the balance is geometry.

Now I don't as much mean the geometry in the case of design, or shape: whether it's ground like a Tanto, or a Kukri, or a Kris. This is the shape you would see in a standard display angle. These designs vary according to aesthetic, culture, and purpose.

Rather, I mean the two dimensions in the point of view as if you were looking at it with the tip pointing towards you. This shaping is what is meant when the term "Edge geometry" is used.

As with many things, there are too extremes. Too obtuse of a bevel angle, and it won't matter how sharp the cutting edge is; it'll act like a wedge rather than a knife. This can be okay for heavier knives, which will drive the edge with much more force, but it's always possible to have too thick of a grind.
Too thin of a grind, and you risk breaking, bending, or reducing the amount of force blade is able to project.

Then there are variations of the grinds. There is a convex grind, often used in thicker chopping knives and swords, and especially axes. There is a flat grind, which as you can guess is a completely flat surface as it goes from the spine to the edge, and is the medium between convex and hollow grind, in which the bevel slopes concave from the spine to the cutting edge. This allows for it to have a very thin angle as the blade begins the cut, then thickening quickly to make up for lost mass and strength.

I have to say, when I started out knifemaking I never payed attention to edge geometry. Back then, my blades were ugly as well as useless, and both, but mainly the uselessness, was very largely due to the grind. The importance of getting it right was only cemented in my mind when I brought a persian fighter with a blade thinner than usual to a creek event, and compared the bamboo-cutting capabilities to that of a friend, who brought a very well built and high quality ka-bar style knife. The ka-bar took two or three strikes to get through 3/4" bamboo, yet my fighter slashed through on the first strike.

Now the incredible bit, is they were the same thickness, within 1/32nd of an inch, and both fairly sharp. Although neither were hair shaving, they were sharp. Also, my blade had about the same blade weight as his, although his hilt was heavier. However, my fighter had a much wider blade.

There are three dimensions in practical design, each can be thought of as a direction. When speaking of blades, the words I will personally use for each dimension are Thick and Thin, Wide and Narrow, and Long and Short. You can envision fairly easily which dimensions these are. Thick/thin is how thick the blade is at the spine, usually between 1/8" and 1/2". Wide/narrow is the measurement from the cutting edge to the spine (back), and long/short is the measurement from the tip of the blade to the guard.

Not just a wider blade, but the bevel extended almost all the way to the spine, rather than stopping halfway on the ka-bar. This meant for a much more acute angle on the fighter, while retaining both weight and thickness at the spine. A good heat treat will further serve against any risk of damage to the blade.

In conclusion, this is my advice and findings: almost all newbies will start out with way too thick of a blade or way too obtuse of a grind. Get as thin and acute as you can, test it out, then modify from there. You are more likely to make a blade too chunky than too thin. With a fixed spine thickness (say 1/4", plenty thick to be a solid, tough blade), you can increase the quality of edge geometry by making the blade wider, and so, the angle more acute. Modify thickness, bevel angle, and blade wideness to make a particular knife ideal for it's job. Take certain knives, say a fillet knife, and a kukri, and mentally list the differences and the purposes, and why any part is just so. Having a firm understanding of edge geometry, purpose, and modification as you make a blade will produce a knife that is the best it possibly can for its assigned application