Before getting into the notion of straight bevels on a knife blade, you need to know that it is the bevels among other things that turn a steel blank into a knife. The predominant majority of blades have varying shapes of bevels, but almost all fit into the general concept that the blade spine is the thickest part of the blade, and the blade area at the secondary bevels is the narrowest part of the blade, not counting the cutting edge. Thus, whether we like it or not, all the blades are more or less wedge-shaped in their cross-section.
Even a beginner may already have a question at this stage, why there are a number of different blade profiles and different types of bevels if most blades have a wedge-shaped cross section. To put it briefly, the difference lies in the details themselves and these details determine the effectiveness of one or the other blade.
In the classical sense, this is a two-sided symmetrical blade with V-shaped or wedge-shaped bevels and secondary bevels that form the cutting edge.
Knives with different profile shapes, which have straight bevels from the spine and a wedge-shaped section of the blade, are indeed more common than other existing types of bevels. This type of bevels is used on a daily basis by users in various activities and seems quite ordinary and understandable. There is a saying that goes like this: "simplicity is the soul of genius", but let us see if it is really that simple.
These are usually medium-sized, large blades and some small blades with a sufficiently thick spine that form a wedge in the direction of the cutting edge.
Classic straight bevels are generally recognized as bevels that taper from the spine directly towards the cutting edge. The blades can have a geometry intended for following creation of secondary bevels. There are rare cases, when the thickness behind the edge is lower than 0.1 mm, or starts at a very high point of the blade (scandi grinds). The shape of the grind and the tip of the blade in our case is secondary and does not matter. For example, we will consider straight bevels of a standard flat grind profile with bevels tapering from the spine, with a belly at the blade point and secondary bevels.
Image 1. Classic straight bevels from the spine or a flat grind
This technical solution of a flat grind blade drawn on the picture above is schematic and the dimensions may vary significantly. Depending on the width of the blade and the angle of the blade belly the bevels of the wedge that from the edge will have different lengths.
The narrower and thinner the blade and the smaller the angle of the belly, the larger the wedge will be in relation to the plain area and the greater the blade cutting effect will be.
Another important technical feature of this type of blades is that with sufficiently high bevels, that is, a large blade width, the secondary bevels can be created at large angles. This is very practical for kitchen knives. A total angle of 40°-42° 0 does not contradict the concept and the blade will cut due to the geometry of the blade, and not just because of the sharpening angle.
Image 2. Classic flat grind bevels with a thick spine
If you change the proportions of this type of blade and increase its spine thickness, you can get a more wear-resistant and powerful blade, but it will become less aggressive. The sharpening angle value of the secondary bevels in this case may be the same and both blades can be sharpened to the total angle of 40°-42° 0 degrees, but their cutting performance will be very different (see the shaded section of the blade in the image).
In reality, such blades are simple to produce, but at the same time they have good cutting qualities and sufficient ability to "split" the object.
These technical aspects are the basis for why most of the different knife types, including kitchen knives, are made with a flat grind with bevels from the spine.
The triple angle bevel is the concept of the so–called "ideal" knife blade, according to which all three geometric projections of the blade should aim at a triangle: profile, cross section and spine.
Image 3. Triple bevel angle
Bevels of this blade type are made to the full width of the blade and produce a rather subtle thickness behind the edge. This geometry has a very good cutting performance even at large sharpening angles.
It should be noted that the mechanical strength of this blade type is slightly reduced, but with proper and correct use it will be just fine.
During production, they usually reserve a slightly larger width for such a blade, because even those blade with a very thin thickness behind the edge will shrink in width by some fraction of a millimeter after sharpening, and the actual thickness at the shoulders of the secondary bevels (at the point of transition of the secondary bevels planes to the bevels planes) will become slightly larger.
Kitchen knives with such bevels and a profile are generally a separate topic in terms of manufacturing complexity.
Combined straight bevels grinds are virtually no different from bevels that start directly at the spine. The only difference is that this bevels type can start at a short distance after the spine.
Image 4. Combined straight bevels
If you compare these blade profiles, visually there will be almost no difference, however, such a blade will differ slightly in weight and cutting quality, which the average user may not notice. You can find such bevels on a number of pocket knives and knives for outdoor use.
Saber grinds are an independent type, each grind comes with secondary bevels, a strong spine, and bevels, which most often start at a distance of 1/3 of the blade width after its spine.
Image 5. Saber grind
Saber grinds are common for tactical and military knives that meet challenging and demanding, high-stress tasks. While the cutting quality of these knives is not the most outstanding, their strength is at a very high level.
Depending on the manufacturer and model, the dimensions of the blades and other parameters may differ.
If we talk about the meaning of straight bevels from the spine, then in this context, such blades are well suited for folding pocket, hunting, fishing and tourist knives, and are also widely used for the production of kitchen knives. Good kitchen knives feature a triple angle bevel on the blade.
It is worth emphasizing that nothing prevents, if desired, to produce a knife with triple angle scandi or convex bevels.
Scandinavian bevel, or as they often call it in everyday life scandi grind, has a wedge geometry with TBE (thickness behind the edge) that is almost equal to 0 or we can say that such a blade has very wide secondary bevels, which most often start from the knife spine at a distance of 2/3 of the width of the blade.
Image 6. Scandi bevels
These bevels are also flat, but differ from the classic straight bevels by a much larger angle and in practical application split the material, rather than cut. This circumstance can be attributed to both an advantage and a disadvantage, depending on the scope of use. At the same time, the mechanical resistance of the cutting edge of a knife with scandi bevels is one of the highest.
Blades with hollow bevels are similar in design to blades with straight bevels from the spine in that such bevels can also be quite high on a knife. Hollow segments create a kind of stiffening rib and also make it possible to leave the TBE at a small value to create secondary bevels.
Image 7. Hollow grind bevels
The width of the TBE may get larger after sharpening and the edge will be more durable and sharp compared to the blade with straight bevels. The hollow and full hollow grinds’ more aggressive cut is provided by their very design, but it does not offer exceptional advantages. This is also due to the fact that it is desirable to use a knife with such a blade for its intended purpose not to damage it. In this aspect hollow and full hollow grinds are somewhat inferior to other types.
Knives that have a convex blade geometry are perhaps one of the less common and this is in many ways completely undeserved. Blades of this type can be used in almost any field as they have a number of technical advantages and only minor disadvantages compared to the others described in this article.
Image 8. Convex bevels
It is very likely that some readers at this point are imagining a massive blade designed for use in nature. However, in practice, it is not difficult to make a kitchen knife with high bevels and a slight convex over the entire area of the bevels and a barely noticeable transition to secondary bevels or with a small TBE with a slightly visible transition.
The advantage of such a blade is that this geometry shifts the angle of lateral load to the secondary bevels plane and significantly increases the mechanical resistance of the cutting edge. Such knives have a very aggressive cut.
Two negative points of the convex grind are the complexity of sharpening, and as a result, a high price, especially in the manufacture of a kitchen knife. Such blades are much more difficult to sharpen and require appropriate equipment and experience.
Before sharpening, it is necessary to choose the right abrasive according to the thickness behind the edge so as not to damage the blade. One should choose bars with a small, preferably medium grits size, because it is quite easy to create a recurve on a straight section. Sharpening bars with a width of 30 - 50 mm are the best, if you want to avoid creation of a recurve.
Besides, you need to pay attention to two areas of the blade: the straight part and the belly of the blade (transition to the tip). We already warned you about the possible mistakes in convex sharpening of the straight part. For the straight part you will spend less time, but after switching to the belly, the contact spot will decrease, and you will have to spend more time on this relatively small area. It also depends on the total length of the plane area. You should consider these moments as a guide.
There is something related to convex bevels and the technique of sharpening straight bevel blades that some will find interesting. It is quite obvious that the angle of lateral load on the convex bevel is smaller. If a blade has small width secondary bevels, it cuts due to its geometry. It is possible to combine both solutions and create convex secondary bevels.
This can significantly increase strength of each secondary bevel and the cutting edge as a whole. However, there is one issue – you need to have experience and the right equipment.
Flat grind knives with blades that have straight bevels are very common in different areas of our lives. Each type of bevels has its own purpose and scope of application. It is the same with knives with straight bevels from the spine.
The blade design itself has a direct impact on the way it cuts and how convenient it is to use it. Mechanical strength, on the contrary, is greatly determined by the type of steel, proper heat treatment, as well as the correct sharpening angle for each specific grind and steel.
This is why you have to choose the right knives with the right grinds for each separate purpose. Do this, and any knife as a tool will make you happy for a very long time.
But do not forget to sharpen your knives, because what is a knife that can not cut? We at TSPROF offer the most convenient knife sharpening solution - precision guided knife sharpening systems. All of our systems are made of a single piece of aluminum, have a trouble-free semi-automatic knife turning mechanism, strong knife clamps and an angle adjustment mechanism.
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