Knife hollow grind
1. About the bevels on the knife blade
Grinding creates a narrowing (bevel) on both sides of the blade and forms the thickness behind the edge (shoulders). In turn, during the sharpening you create secondary bevels in front of the thickness behind the cutting edge.
Bevels of the blade, along with the steel are one of the main criteria for evaluation of the cutting performance of a knife. A blade without bevels is just a piece of steel that cannot fulfil its intended purpose.
There are several basic types of knife blade grind profiles and several variations depending on the ingenuity of the designer or the knife maker.
Blade grind with the shape of hollow bevels is a very common technique for creating knife blades and we will discuss it further. Knives with these grind of bevels have excellent cutting abilities, better than a flat bevelled blade and in some respects they are more flexible than others.
Knives with such bevels are very often used for hunting and hiking. In some cases, they produce high-end kitchen knives with this type of bevels and knives get a scary sharp cutting edge.
Due to their design, hollow bevels are very often associated with the most familiar household item - a dangerous razor, which appeared according to some sources in England, in the city of Sheffield in about 1680 and from there it got a worldwide distribution. Hollow grind bevels are often referred to as razor bevels.
2. Hollow grind bevels blade design
The classic design of many dangerous razors has hollow grind bevels running almost from the spine of the blade. There is a special sharpening method that is used to create hollow grind bevels.
The essence of this method is that the grinding starts from the back of the blade at about 1/3 of the blade width, and then with a smooth rounding descends towards the cutting edge. The thickness behind the edge of the blade depends on the diameter of the grinding wheel or abrasive disc. As a result, you get a rather small thickness behind the edge and as a consequence a blade with a cutting edge that is much thinner and sharper than all other types of bevels.
3. Modern blade types with a hollow grind
Nowadays, due to the development of steel production technology and developments in metalworking equipment, it is possible to produce not only classic bevel types, but also to create new ones.
Below you will find the structure of a classic blade with hollow ground bevels.
1 - blade width, 2 – spine, 3 – blade flat, 4 – bevels, 5 – secondary bevels, 6 - thickness behind the edge
1 - spine, 2 – sharpening angle, 3 – bevels, 4 – secondary bevel, 5 – cutting edge
3.1. Classic hollow grind bevels
As mentioned above, there are classic hollow grind bevels that have a 2/3 of the width of the knife blade. Such knives have the widest distribution and are used for various household purposes. Due to this you can call them the classic type of hollow grind bevels.
The advantage of knives with classic hollow grind bevels is that such blades combine sharpness and stability thanks to the presence of the blade flat, i.e. due to the 1/3 flat area of the blade from the spine and the hollow grind bevels. As a consequence, such knives have a sharper cutting edge compared to blades with flat bevels or blades with flat bevels that take 2/3 of the blade width. Knives with hollow grind bevels and a thin cutting edge are best for cutting thin objects and soft foods.
Another advantage is that hollow ground bevel blades retain their geometry for a longer period of time, and thus have a longer service life until their secondary bevels become too thick.
However, this blade type still has disadvantages, e.g. when cutting through thick and dense foods, such as carrots, in which it has a great possibility of stucking. Due to the small steel thickness behind the edge, the blade is also vulnerable to chipping and rolled over parts due to the high lateral loads. Such a blade is inferior in strength and reliability to blades with flat and convex grind bevels and convex grind secondary bevels.
They often make blades of hunting knives, camping knives and various folding pocket knives with this type of bevels, if they have sufficient width and thickness of the blade.
Buck folding knives and their like are classics of this genre.
3.2. Hollow grind bevels from the spine
Knives with this version of this type of bevels are not very common. Technically it is very difficult to start removing steel right from the spine of the blade, so usually the removal starts in the vicinity of the blade spine. This removes most of the steel from the blade. The whole point of using this approach is to make a blade with the smallest thickness behind the edge and a sharp cutting edge.
The use of this geometry is appropriate for narrow, thin blades that are designed specifically for cutting. That said, these knives can be either folding or fixed. Even the small radius of hollowness gives the blade a much higher cutting ability, compared to the same blade with flat bevels.
Hollow ground geometry is seriously inferior to a blade with convex bevels and convex secondary bevels, i.e. full convex, in terms of strength of bevels.
The most obvious areas of use for such bevels are hunting knives and carving knives. The knife with a fixed flat blade and hollow grind bevels almost from the spine, with a comfortable handle is the best solution for processing large quantities of meat.
3.3. Combined bevels
Blades with combined bevels is a product of the modern era, although there are some national knives with combined bevels. You probably encountered knives that had different geometry on both sides of the blade.
They often combine flat grind bevels with convex bevels and hollow grind bevels with flat bevels. This allows you to create a blade with different zones of strength and different sharpness.
They create hollow grind bevels on the flat part of the blade and they often take most of the blade area, while flat or convex bevels are used to strengthen the tip and the point. Such a knife blade has an area that can be quite sharp, and a strong tip able to withstand considerable stress.
This kind of grind can be found on the blades of modern folding tactical knives produced by Benchmade, Borka Blades, Olamic Cutlery. There are different opinions regarding utility of such knives and blades.
4. Hollow grind blades – quality or a mass consumption commodity?
To understand the nature of blades with hollow grind bevels you need to get a little insight into some of the details of their geometry:
- If you grind a straight rectangular workpiece with a given diameter, you will end up with something similar to a triangle in the cross-section.
- The next step is to shape the point into a sharp-edged piece.
- You can give the knife workpiece a good marketable look if you remove excessive material at the knife tip.
If you do this, you will end up with areas of different thicknesses behind the edge.
The idea behind creating a hollow grind blade is to have the abrasive follow a curved line at the cutting edge area. The curved movements should come from the belly area smoothly transitioning from the horizontal to the vertical plane. If you look at some of the blades with hollow grind bevels, you will see straight away how much quality was involved in the production of this or that knife.
All of these circumstances directly affect the cutting quality of the knife and the possibility of sharpening it using this or that method.
5. How to sharpen hollow grind bevels
The sharpening of hollow grind razor bevels can be compared to sharpening the edges of a Japanese chisel. The main point of sharpening such a chisel is to grind the bevelled plane. A razor can be sharpened using the same method during the classic manual sharpening.
However, sharpening a knife with classic hollow grind bevels is somewhat different from this method. In general, it's all about finding the right angle. Even though the thickness behind the edge is less than on all other blades, you need to find an angle that suits the knife's intended purpose.
If you use a pocket knife as an every day knife, you may want to set a greater sharpening angle to increase the cutting edge retention. If the knife is a kitchen or a carving one and is used carefully and for its intended purpose, you can set a shallow sharpening angle for the edge. Such a knife can cut well simply because of its grind.
If the knife was manufactured properly, it will have a consistent thickness behind the edge and uniform identical secondary bevels and vice versa if the bevels were not profiled properly.
Sometimes it can be a problem to sharpen combined bevels. A blade with hollow grind bevels may, among other things, have a recurve shape, which makes it all the more difficult to transition from a small thickness behind the edge to a larger thickness behind the edge at the tip. Keeping the same angle is often too difficult and just does not make practical sense.
6. Technical features of use and conclusions
Some types of knives have a rather narrow purpose and knives with classic hollow grind bevels are no exception. If you use them well and properly, without side loads and not for hard objects, like bones, they can last a very long time.
On the other hand, more advanced knives with combined grind bevels and thicker blades are more durable, although they serve completely different purposes.
The choice of steel and type of bevels must be made by each individual on their own, depending on the purpose for which their knife will be used.
Kitchen knives — are professional tools that remain sharp and reliable only with proper care and storage. Both the professional chef and the amateur must know how to use and sharpen the knife, how to clean it and treat it...