III. Blade Grinds
- The Hollow Grind
The hollow grind is done by taking two concave scoops out of the side of the blade. Many production companies use this grind, because it's easier to design machines to do it. But many custom makers grind this way as well. Its great advantage is that the edge is extraordinarily thin, and thin edges slice better. The disadvantage is that the thinner the edge, the weaker it is. Hollow ground edges can chip or roll over in harder use. And the hollow ground edge can't penetrate too far for food-type chopping, because the edge gets non-linearly thicker as it nears the spine.
For designs where slicing is important, but the slice doesn't need to go too deep, this grind is an excellent choice. Many hunting knives are hollow ground, because field dressing is often best done with a knife that slices exceptionally well through soft tissues. Unfortunately, if you hit a bone, you can chip the edge, so the flat grind (see below) is also used often.
Another advantage of the hollow ground knife, at least at the beginning, is ease of sharpening. Most hollow grinds thicken slightly towards the edge. That means that as you sharpen (at least at first), the blade gets thinner and easier to sharpen. After this, however, the blade begins thickening non-linearly and sharpening will become more difficult.
The ultimate push cutter, the straight razor, is usually hollow ground.
- The Chisel Grind
The chisel grind is a knife which is not ground at all on one side. So it is completely flat on one side, and has a bevel on the other. It is simple to produce (the maker need only grind one side), and simple to sharpen (it is sharpened on one side only, then the burr is stropped off the other side). It is also typically very sharp, due to the single bevel design. Whereas a blade ground on both sides might be sharpened at 20 degrees per side, for a total of 40-degrees edge angle, a chisel ground blade is often ground at around 30 degrees, making for a thin (and thus sharp) edge.
Accurate slices are very difficult with the chisel grind, due to the fact that the non-symmetrical design forces the knife to curve in the medium being cut.
- The Sabre Grind
The sabre grind is a strong edge format. The bevel starts around the middle of the blade, and proceeds flatly towards the edge. This leaves a strong edge for chopping and other hard use. But it also means the edge will be fairly thick, so this design will not necessarily slice all that well.
The sabre grind is found on many military classic designs such as the Randall #1 and the kabar.
- The Flat Grind
The flat grind endeavors to provide an edge that is both thin and strong, and leaves a strong thick spine. The grind is completely flat, going from the spine to the edge. This grind is harder to make, because a lot of steel needs to be ground away. However, the edge ends up being fairly thin and so cutting very well. Because the bevels are flat, there is plenty of metal backing the edge, so it's much stronger than a hollow grind. It is not as strong as a sabre grind, but will outcut that grind.
The edge on this design also penetrates better for slicing and chopping. The hollow grind expands non-linearly as you go up the blade, the sabre grind expands linearly but very quickly. The flat grind expands linearly and slowly. Kitchen knives are usually flat ground, because when chopping/slicing food you need to push the blade all the way through the food. This grind is an outstanding compromise between strength and cutting ability, sacrificing little for either.
- The Convex Grind
Also called the Moran grind, after Bill Moran. This grind is as you would expect, the grind arcs down in a convex curve down to the edge. This means the point can be very sharp, because there's no secondary bevels to create the edge itself, just two intersecting arcs. There is also a fair amount of steel behind the edge, because the convex arcs cause the edge to widen non-linearly. This is a strong-edge format, which won't penetrate like a flat grind but will be stronger. Knifemakers form this grind on a flat-belt grinder. A disadvantage of this grind is if you don't have a flat-belt grinder yourself, it is difficult to touch up the edge.
