How to Sharpen a Convex Edge

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Even though the key reason for a blade to exist is to cut, not all blades are created equal. More to the point, they don’t uniformly cut the same way. There’s nuance to every cut they make. This ensures that one blade might be suitable to certain jobs while another blade should be used on other jobs. Things like blade length, steel type, and crafted edge can change the cutting ability or function of your knife as well as its durability.

With that said, let’s talk about how to sharpen a convex edge. We’ll also cover a few of its key benefits as well for good measure.

What Is a Convex Edge?

The convex edge, also known as the Moran grind, is a rounded type of edge that tapers off to the finest point of the blade’s cutting edge. It’s considered the superior grind type for many reasons, chief among them its durability because of how rounded it is and how it wears down. When cutting, there’s also less drag due to its shape. Many other grind types have a tapering straight line or concave edges instead, which by the Laws of Physics result in more of a drag.

Although the usual school of thought regarding edges is that sharp is sharp, some types of sharpness are more convenient for your tasks than other. The convex edge isn’t just a fancy grind type that’s a fad or something. This edge has been around for a while for a reason. This rounded edge was made by bladesmiths due to its ease to forge with a hammer. It’s also not so much fancy as simple—you don’t need intricate skills to make this edge type.

Equipment

Towel
Guide rod
Convex-edged knife

Faucet or water source
Whetstone (fine, medium, and coarse)
Custom sharpener with moldable surface

How Do You Sharpen a Convex Edge?

The grind is a technical term for the type of edge the blade has. It’s the point where the blade begins to take shape so that it narrows down to the sharp edge. There are many types of grind, and the convex edge is just one of them.

1. Using a Whetstone or Not

Soak the whetstone for 10 minutes first. Afterwards, keep things slightly wet for it as you use it to create your convex edge bevels. Don’t forget to dribble a little water on it from time to time to keep its moisture levels up. As for the towel or some other absorbent material, it’s there to ensure that your stone has enough grip when you do your sharpening to prevent slippage and whatnot. If this confuses you, order an Original Knife & Tool Sharpener or something similar to do the work for you.

2. Depends on the Knife

Grinding and sharpening a convex-edged knife mostly depends on getting the right angle for sharpening. For a knife with a rounded edge, you might choose to sharpen it at a 20° angle on each side. This is as opposed to a V-grind that uses flat bevels. Aside from a block of whetstone, you can instead use a soft, moldable surface to create a contoured sharpening stone that isn’t a flat whetstone block. You can round off edges there easier to make that convex edge.

3. Varying Angles

A convex edge knife can’t be sharpened like usual with whetstones since they mostly work with plane beveled knives. It’s because the curved bevel surface can’t be sharpened or ground properly with tools designed for flat edges. You can either create a primary and secondary bevel as discussed above or vary angles as you sharpen the rounded edge of your knife. This involves doing a curved motion as you pass the knife on your whetstone. Don’t come up past where the apex is.

4. Higher or Lower Angles

The 20° default angle for convex edges can go higher or lower depending on the quality of your blade’s steel and the way you plan to use the kitchen tool. The 20° angle for convex-edge grinding we’re using is based on convex-edged chef’s knives with medium stainless steel quality that’s mainly designed for cutting up fruits and vegetables in the kitchen. In order to sharpen an existing convex edge, you need to make a primary bevel that’s narrower than your final bevel.

5. Using the Guide Rod and Forming Burrs

Set the L-bracket of a guide rod (like “The EdgePal Chef”) to 18° then tighten the thumbscrews. Get a course whetstone to grind the bevel until they reach the shoulder to the edge. When scratches appear to reach said edge, focus on one side until burrs start forming when you scratch the edge with a cotton swab or a fingernail. Switch sides and repeat the grinding process. Work until you’re able to raise burrs on either side of your blade.

6. Polish The Primary Bevel

After raising a burr long the entire length of your convex-edged knife on either side of it, you can now switch to a finer grit of whetstone. Polish the scratches from the course grit stone away. You will feel the particles of the stone go into contact with the bumps and holes of scratches left by your previous grinding. Each stroke on a consistent angle you’ve chosen should turn the edge smoother every time.

7. Making the Secondary Bevel

Switch to another grit level for creating the secondary bevel of your convex edge. Move the L-brackets to 19° and tighten the thumbscrews. Use your finest sharpening stones and do alternating strokes on it to make a bevel on each side that extends about ⅓ the distance down to the primary bevel towards the shoulder of the blade. This should give you the 20° convex edge on either side. Smoothen away the bevel in order to get the rounded edge when you’re done.

In a Nutshell

The main thing that gives people pause about sharpening a convex edge is that they’re more used to flatter edges found in the most common knives and blades. They can’t wrap their heads around the concept of bevels and different angles of sharpening. Once you get your hands on a guide rod and learn how to make bevels to round the edge of your knife, it should be an easy enough concept to comprehend.

Depending on the level of dullness of your knife, you can either recreate the edge with a coarse grit stone moving down to finer grits or just polish the cutting edge your knife already on two different bevels.

How to Sharpen a Convex Edge?