Knife Sharpening Angle Basics – Sharpness Vs Edge Durability
Selecting an angle to sharpen your knife is about understanding the tradeoff between sharpness vs durability. At the most basic level, lower angles are sharper, and higher angles are more durable. Understanding when and why you might sharpen at a higher or lower angle will help you answer one of the most common sharpening questions.
What Angle to Start
If you’re looking for a place to start, we often consider 20 degrees to the midpoint of where to start. Angles lower than 20 degrees are often considered lower, while above 20 are higher angles. In this article, we’ll consider the factors that will affect your angle decision.
This is what we call the sharpening angle. It can also be described as degrees per side. When you sharpen both sides of a knife, that is called the inclusive angle.
Let’s get a few definitions out of the way to make sure we’re communicating the information accurately. Unless otherwise stated, it will be the sharpening angle or degrees per side when we mention angles. Said another way, when sharpening a knife you sharpen each side, so your inclusive angle is double the sharpening angle. Since this article is more about explaining the basics, we will focus on the vast majority of knife edges that are sharpened equally on both sides. For example, if you sharpen at 20 degrees, both sides add up to an inclusive angle of 40 degrees. When we say 20 degrees, this is the angle you sharpen your knife.
Edge failure is one aspect of durability that is greatly affected by the edge angle. An edge failure can be rolling, folding, or even chipping an edge. An edge failure can occur quickly and greatly affects the sharpness of an edge more than normal wear.
Sharpening at Lower Angles
Sharpening at a lower angle will create a sharper edge. If maximizing sharpness is your goal, a lower angle will generally create a sharper edge.
The lower bound of your sharpening angle is limited to the type of steel and the usage. Higher-quality steels tend to tolerate lower angles. The wording of “tend to” is intentional here as this is not absolute. The other factor is usage, a knife cutting very soft materials can tolerate much lower delicate angles. For this reason, a kitchen knife can often be sharpened at lower angles, especially if used to slice softer foods.
If you’re looking for the absolute lowest angle on a knife, that would be roughly 10 degrees. For comparison, a straight razor blade is generally sharpened to 7 degrees and that edge can fail while cutting anything harder than a whisker.
Sharpening at Higher Angles
Sharpening at a higher angle will create a more durable edge. A durable edge won't fail so it can retain its sharpness longer.
Sharpening even harder steel to a higher angle may allow it to resist damage and allow for a greater variety of uses.
When sharpening to higher angles, we’re typically talking about angles greater than 20 degrees. Even adding a few degrees can increase the durability of an edge. A very high angle such as 30 degrees is nearing the practical limit of the edge and may not be necessary for all but the softest steels or most extreme durability needs.
This very damaged blade is one way an edge can fail. One of the more common causes of edge failure is sharpening at too low of an angle.
Sharpness And Durability is Relative Not Absolute
If you’re interested in the topic at a deeper level, it is important to think of angles not as absolute, but as relative to one another. While 20 degrees is considered an inflection point for higher or lower angles, that is not true in all cases. The type of knife and its usage will affect what may be considered high or low. For example, a knife used to cut sushi might be considered high above 15 degrees and a knife used to chop wood would be considered low below 22 degrees.
Test For Yourself
Now that you understand the tradeoffs between angle and durability, it is time to put your knowledge into practice. A good place to start is on a knife that never quite seemed to perform as expected. Find a knife that has a rolled edge and give it a higher angle, you might find that it performs better at a higher angle. Or find a knife that never seemed to get sharp enough and experiment with a lower angle. If you want to try a few different angles on a knife, start low and then go higher, adding degrees is a much quicker process.