Flat, hollow or convex grinds? And why

Flat, hollow or convex grinds? And why

The grind used on a knife blade lends itself towards different applications and each has their own advantages and disadvantages. Some are physically stronger, others are sharper, and some try to find a balance of both. A trade-off exists between a blade’s ability to take an edge and its ability to keep one. Some grinds are easier to maintain than others, better retaining their integrity as repeated sharpening wears away the blade. All knife grinds are good, if matched to a particular application. The convex grind is very strong, the hollow is great for cutting, with the flat grind represents a balance between strength and sharpness.

An appropriate grind depends upon a blade’s intended use and the knife steel composing it. Knife manufacturers may offer the same blade with different grinds and blade owners may choose to regrind their blades to obtain different properties.

Harder steels take sharper edges, but are more brittle and hence chip more easily, whereas softer steels are tougher. The latter are used for knives such as cleavers, which must be tough but do not require a sharp edge. In the range of blade materials’ hardnesses, the relationship between hardness and toughness is fairly complex and great hardness and great toughness are often possible simultaneously.

Flat grind / Sabre / Scandi

  • What it is: A flat grind is a single, symmetric V-bevel — the blade tapers from a particular height on the blade and ends at the cutting edge. A flat grind that begins at the blade’s spine is called a “full flat grind”; a “saber grind” begins its bevel lower on the blade; and a Scandinavian (or “Scandi”) grind begins lower still. Technically, all are flat grinds.
  • What it’s good for: Whittling, woodworking, food preparation, general use.
  • How to sharpen it: A flat grind can be sharpened on a stone or other flat hone, or by using a guided sharpening system.
  • What you may not know: The flat grind is the simplest and most basic profile. It’s easy to maintain, but it doesn’t produce the most durable edge. For that reason, a knife with a true flat grind is relatively rare. (Most blades billed as having a “flat grind” actually have a secondary bevel.)

Scandi grinds are a variation on a full flat grind and are remarkable tools for woodcraft and carving. Nothing comes close to way a scandi shaves wood. You lay the blade on the large flat bevel and it naturally aligns the edge. Thus the material the knife is resting on keeps it aligned through the shave.

Hollow grind

The hollow grind is the predominate knife grind used by South African knifemakers. They have the lowest strength of all designs including scandi as a large portion of the blade is thin relative to the spine. They tend to cut well because they are easy to sharpen as per above. They don’t tend to slice all that well because they wedge out where the hollow grind ends and intersects with the spine.

  • What it is: A hollow grind features symmetric, concave surfaces ending in a thin, extremely sharp edge. A hollow grind doesn’t produce a very strong edge, and therefore generally isn’t suitable for sustained use on hard or fibrous materials.
  • What it’s good for: Straight razors (shaving), hunting (skinning), food preparation (slicing), axes (special “speed grind” used on some competition axes).
  • How to sharpen it: Traditionally, hollow-ground straight razors have been sharpened on leather strops, aided by abrasive stropping compound. Most of the hollow-ground knives produced today have a secondary V-bevel at the edge, and so can be sharpened on a stone or other flat hone, or by using a guided sharpening system. Because a hollow-ground blade has the potential to be extraordinarily sharp, however, it can benefit greatly from stropping.
  • What you may not know: The concave surfaces of a hollow grind tend to draw the work against the blade and toward the edge before the flat surfaces (higher on the blade) push it away, which is why many knife lovers prefer this profile for slicing and skinning.

Convex grind

  • What it is: Is the opposite of the hollow, in that the sharp edge is produced by symmetric, gently curved surfaces towards the edge. Such a shape keeps a lot of metal behind the edge making for a stronger edge while still allowing a good degree of sharpness. This grind can be used on axes and is sometimes called an axe grind. The point where the curvature begins (high or low on the blade) can produce a full convex, a saber convex or even a Scandi convex grind.
  • What it’s good for: Many knife aficionados consider a convex grind the strongest and most durable profile as the thicker edge leads to less cracking and chipping. Hunting, woodworking, food preparation, axes, general use.
  • How to sharpen it: Sharpening a convex grind requires an abrasive surface that ever-so-slightly “gives” to follow the curvature of the blade — generally, a leather strop or hone (a piece of leather affixed to wood base, with abrasion provided by stropping compound or sandpaper).
  • What you may not know: A practiced hand can sharpen a convex-ground knife on a hard surface or a flat stone. Because it’s relatively difficult to master, however, this technique is best reserved for emergencies in the field. Convex blades usually need to be made from thicker stock than other blades.[1] This is also known as hamaguriba in Japanese kitchen knives, both single and double beveled. Hamaguriba means “clam-shaped edge”.

Chisel grind

one bevel. sharpened straight to thte edge. insainly sharpe. slicing soft materials. fragile edges.

  • What it is: A chisel grind essentially is a V-bevel, except that only one side of the blade is sharpened while the other side remains straight (like a wood chisel) making for an insainly sharpe edge that is great for slicing soft materials.
  • What it’s good for: Woodworking, food preparation. Also common on some military and “tactical” knives.
  • How to sharpen it: Sharpen a chisel grind as you would any other V-bevel (including by using a guided system), except that only one side of the blade is honed (often at an edge angle of about 20 – 30°). It’s advisable to lightly draw the opposite (straight) side of the edge across the hone occasionally, to remove any burr that may develop during sharpening.
  • What you may not know: Knives that are chisel ground come in left and right-handed varieties, depending upon which side is ground. Japanese knives feature subtle variations on the chisel grind: firstly, the back side of the blade is often concave, to reduce drag and adhesion so the food separates more cleanly; this feature is known as urasuki.