Knife Edge Geometry Types

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Knife Edge Geometry Types

Hollow Grind or Concave Grind

a knife blade ground to create a characteristic concave, beveled cutting edge. This is characteristic of straight razors, used for shaving, and yields a very sharp but weak edge, which requires stropping for maintenance. Basically, a hollow grind is made by a wheel to “hollow” above the edge. This helps by removing the metal about the edge to reduce the drag and helps with sharpening.

Strengths: Very good slicing ability, easy to sharpen.

Best knife types: Skinners / Hunting Knives, Small to medium sized Everyday Carry blades, and Straight Razors.

Weaknesses: The edge can be fragile compared to other grinds. No chopping. Grinding wheel costs might limit blade design.

Flat Grind

the grind goes all the way down from the spine to the edge bevel in a flat, linear slope. The flat grind is one of the most versatile grinds. It can be thick and heavy, or it can be extremely thin and sharp. Or it can be a balance between the two. Most flat grinds are a balance between the two, though it will depend on the design.

The full flat grind is thickest at the spine for strength but tapers down into a relatively thin edge for excellent slicing. More steel is removed from the sides, allowing for easier slicing and allowing the blade to move through mediums easier. A full flat grind will (typically) be stronger than a hollow grind and cut better than the sabre grind.

The full flat grind has a great mix of the strengths of the other two grinds. Because it is a great all-rounder, the full flat grind is one of the more popular grinds.

Strengths: Good cutting, strength, and chopping (depending on blade thickness).

Weaknesses: Doesn’t cut quite as well as a hollow grind, isn’t quite as robust as a sabre grind.

Sabre Grind

A sabre grind is either a flat or hollow grind where the primary bevel (the grind) does not cover the entire width of the blade, leaving some portion unground. If someone says “sabre hollow ground” you know the blade has a hollow grind that starts partway down the blade. The transition line between the primary bevel and the unground portion of the blade is referred to as the Sabre Line.

The sabre grind is used when the maker wants a stronger blade. To make full use of the stronger blade, often the stock is kept a little thicker so that the blade can stand up to hard use, such as chopping. With a thicker stock, the sabre grind will not slice as well as other grinds. Classic military designs utilize the sabre grind.

Strengths: Excellent durability. It will hold up to chopping or penetration.

Best Knife Types: Military & Tactical Knives, Self-Defense blades, Camp Knives.

Weaknesses: Its cutting ability is typically less impressive than other grind types.

Chisel Grind

The chisel grind is not ground on one side at all. It is completely flat on one side, and has the primary bevel only on one side. The chisel grind may or may not have a secondary edge bevel. The knife pictured above, and the profile diagram picture to the left, are both sabre chisel grinds. You can see how the bevel starts partially down the blade. A full chisel grind would have the bevel go all the way up to the spine.

The chisel grind is easy to make, as you only have to grind one side, and you don’t have to make the grind symmetrical with the other side. The chisel grind is also easy to sharpen for the same reason – there’s only one side to sharpen (and then strop off the burr). Because one side is left unaltered, the other side can be sharpened at a thinner angle, making for a thin, sharp edge.

Achieving accurate cuts is difficult with the chisel grind due to the unsymmetrical design. The blade will curve into the material being cut. So the knife will naturally slant towards the beveled side, causing the cut to be slanted as well. Sometimes this is preferable, such as with handmade Japanese Sushi knives. When cutting fish quickly, a symmetrical grind might suck the meat in on both sides, which might accidentally suck in the hand you are using to hold the fish steady. By using a chisel grind, you can have the blade cut away from your steadying hand, and the meat will not be sucked in on the unground side.

Chisel grinds tend to be rare and are not used very often. Think of them as a specialized grind. Typically a knife with a chisel grind has a specific purpose.

Strengths: Excellent strength, good chopping (depending on angle), easy to sharpen, can have great cutting ability (again – angle).

Best Knife Types: Sometimes found in choppers such as machetes or other bushcraft knives. Can also be found regularly in traditional handmade Japanese Kitchen Knives.

Weaknesses: Cutting is not symmetrical which can be confusing, performance can vary widely – depending on grind angles and design.

Convex Grind

The convex grind was found on the knives made by early American blacksmiths with no understanding of the way knives were made by those who made a profession of knifemaking in their day. Convex “grinds” were easier to make with a hammer, which is why they were popular in those early days. Nowadays, a slack belt grinder is used to make the convex grind. Convex grinds have also been made popular by the followers of the Moran cult established by the writings of Ken Warner about his friend Bill Moran. Consequently, it is also known as the Moran Grind. It is also sometimes referred to as the Appleseed Grind.

The convex grind arcs down into a convex curve (arcs out) towards the edge. The convex grind is similar to the sabre grind in that it (typically) still has a lot of steel in the middle of the blade, making it the thickest of the three main types of grinds. This puts extra steel behind the edge, reinforcing and strengthening it. The convex grind technically does not have an edge grind (edge bevel), the grind curves all the way into the edge. In practice, convex grinds often do have a small edge bevel, or a “micro” edge bevel, especially after being resharpened.

 The main drawback of the convex grind is that can be difficult to sharpen. My method to sharpen convex grinds is to take something flat with a little give, such as a thick mouse pad, and put some sandpaper or an abrasive on it and use backward strokes (away from the edge) on the knife to give it a “micro” beveled edge. You’ll of course need to go through several grits to bring the knife back up to sharp. Afterward you’ll need to strop off any burrs since you are using the backward stroke method.

The convex grind is widely used with axes, and sometimes with machetes. Bolos and Kukris sometimes use the convex grind as well. The thick edge can take a beating without chipping or rolling. Not all choppers use the convex grind. You can get similar strength with a wide angle on a flat ground blade with a thick edge bevel.

In my opinion, the convex grind is useful only in large chopping blades and axe formats. I do not think the convex grind is useful in smaller knife formats. There are some who disagree with me. You will have to come to your own conclusion about it.

Strengths: Very strong edge, great for chopping. Good for cutting things that need a lot of force, like bone or wood.

Best Knife Types: Choppers, Machetes, Axes, some larger bushcraft knives.

Weaknesses: Difficult to maintain and sharpen – requires skill, and uncommon sharpening tools. Can have difficulty carving, not the greatest slicer. Performance can vary wildly depending on angles.

Scandi Grind

The Scandinavian grind, or Scandi grind, is a short flat (occasionally convex) grind on a thin blade where the primary grind is also the edge bevel. This means that you do not have a secondary edge bevel/grind at all; there is only the one primary grind which is ground to zero to make the edge, sometimes called a Zero Sabre Grind. This leaves a lot of material behind the edge, strengthening it.

The benefit to using a scandi grind is that you can use the entire primary bevel to guide your knife along the bench stone as you sharpen it. Just put slightly more pressure on the very edge to form a miniscule edge bevel (it won’t be visible). Of course, for this to be a benefit you have to use bench stones as your sharpening device.

The downside to a scandi grind is the flip side of the coin of having a lot of material behind the edge. While the edge is strengthened, it also means that you have to remove a lot of material to remove when you sharpen it. Personally, assuming I was forced to use one, I would attempt to make a “micro” bevel on the edge through the use of ceramic rods or as mentioned with convex grinds with a slack belt or sandpaper with some give to it, rather than sharpening the entire primary bevel.

I do not recommend turning your knife with an edge bevel into a scandi grind. If the maker designed the knife to have an edge bevel, then turning it into a scandi grind will often make the blade too thin and will have a weak edge. Only use the scandi grind if the knife originally came with a scandi grind.

Strengths: The theory of sharpening a Scandi is easy to understand. Often has a strong edge that doesn’t chip easily (depending on grind angle)

Weaknesses: Not as good at slicing as other grinds. In practice, sharpening can be a chore as you have to sharpen the entire bevel (and remove a lot of steel) to sharpen it, assuming no micro-beveling.

Next you should see Knife Patterns

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