The majority of knives will have a bevel on both sides and need to be sharpened on both sides. So if a 20-degree angle is necessary for your knife in most circumstances that means you need to sharpen the knife on both sides at an angle of 40 degrees total. There are some traditional knives from China and Japan that only have a bevel on one side. However, most “Asian Knives” sold in Western countries tend to be beveled on both sides as well. It’s usually safe to assume that you will need to choose the correct angle for both sides of the knife.
Sharpness Vs Durability
When sharpening you are actually removing metal from the blade itself to refine the edge. The more metal you remove the sharper the blade is, but the less durable it becomes especially over time as more and more material is removed. When you sharpen a knife you are essentially making a compromise between sharpness and durability. Which is more important to you? Consider the following: If you are shaving your face will you need a sharp blade or a durable blade? On the contrary, if you are chopping wood with great force is a razor sharp blade as crucial for splitting a log as it is when you are removing hair from your face? Not quite.
The wider the angle is the more durable the blade is. A blade with an angle greater than 30 degrees is far more durable than a blade with an angle of 10 degrees. However, the degree of precision when cutting is going to vary significantly. The 10-degree blade obviously will be a lot sharper and require a lot less brute force to slice properly.
Bevel Angle Guide
Durability By Degree Of Angle
For more details about how the degree of the angle can affect the durability and sharpness of the knife refer to the breakdown below.
Under 10 Degrees
Blades that would be sharpened under ten degrees include blades like scalpels and razors that rarely would suffer the amount of abuse that a hunting knife would. These knives are the least durable, but they are also the sharpest. When you are trying to obtain the closest possible shave this is crucial.
This would be on the low side for most blades and rarely would you ever be sharpening a knife at this angle. This angle is used mostly for slicing cooked meats and other soft items. It provides a smooth cut, but this bevel angle would not be used for something like dicing an onion or cutting through raw flesh.
This range is considered the compromise between sharpness and durability. Most knives in this range are sharp enough to chop, dice, and slice and durable enough that they can withstand quite a bit of abuse. Japanese knives will often be sharpened to the lower end of this scale whereas most kitchen knives from the West will be around 20 degrees.
This edge will not cut as well as the knives in the previous category, but it can withstand quite a bit more abuse and use. Pocket knives or hunting knives might fall under this category. Generally, they will be used in more rugged situations than a kitchen knife and have to withstand cutting through a bit harder material.
Angles Over 30 Degrees
These knives will be the most durable, but there will also be a noticeable lack the sharpness of the blade when cutting. An example of a sort of knife that would use this angle would be a wood axe used to chop wood. The sharpness of an axe doesn’t need to be anywhere near that of a straight razor as the requirements for chopping a log of wood are obviously going to be quite different than shaving the hair off one’s face.