If you are new to sharpening and are just getting the hang of it, you might wonder about the grit size of your sharpening stones. Most likely you will say, «What kind of sharpening stones do I need?» To answer this question, we need to clarify a number of points related to the sharpening stones materials and the grit size.
However, you should understand not only what sharpening stones are made of, and what grit sizes are available, but what exactly a particular sharpening stone with a particular grit is designed for.
The sharpening stone should be chosen depending on the purpose of the knife and the quality of the steel from which the blade is made. You should also keep in mind that one single sharpening stone with one particular grit is not enough to achieve an acceptable result.
For starters, you should know that there are a number of industry standards and grit classifications of abrasives and that different manufacturers use different systems to describe their products, which creates certain challenges in understanding and identifying the grit itself.
When comparing grit sizes, it is common to use grit charts, but they do not reflect the whole picture, and with many things, you have to rely on personal experience to be sure.
In a broad sense, the grit of the abrasive material or, in our case, sharpening stones or bars, should be understood as the size of the average grinding particle in the fraction, which is measured in certain units.
If you try to solve your grits choice problem by focusing on certain units of comparison, you are on the right track, but you should know that there are disadvantages and limitations within all standards.
The most familiar and most common grit classifications are the following:
As a beginner, you should understand that within each standard and depending on the manufacturer, there is a specific grit range. For example, FEPA-F has F500 and F600 grit, but there is no F550 or F650 values. This means that the values are discrete, that is, not continuous.
This is because any abrasive consists of a very large number of particles, and the value indicated is the one that is, in fact, predominant in a given sharpening stone. In fact, no industrial particle filtration process in production can produce an abrasive in which all particles will be exclusively the same.
Quite often manufacturers in the U.S. use other concepts to simplify the classification system and bring it closer to reality. That is, they use a verbal description of the common numerical values.
This principle is used both by manufacturers and sellers of abrasive stones. You have surely already encountered such basic concepts as coarse, medium, and fine. These are just three levels out of a possible ten.
|
Group |
Description |
particle size, µ |
FEPA-F |
JIS, grit |
|
1 |
Extremely Coarse - |
100+ |
F150 |
< 150 |
|
2 |
Coarse - |
60 - 100 |
F180 |
150 |
|
3 |
Medium Coarse - |
45 - 60 |
F230 |
220 |
|
4 |
Medium - |
35 - 45 |
F240 |
300 |
|
5 |
Medium Fine - |
25 - 35 |
F280 |
400 |
|
6 |
Fine - |
15-25 |
F360 |
600 |
|
7 |
Extra Fine - |
8 - 15 |
F500 |
1000 |
|
8 |
Extremely / Ultra Fine - |
4 - 8 |
F800 |
2000 |
|
9 |
Near Mirror Polish - |
2 - 4 |
F1000 |
6000 |
|
10 |
Mirror Polish - |
0 - 2 |
F2000 |
10000+ |
Anyway, all the so-called groups of stones lead to the expression of grit in numbers and give a description of the possible result that can be achieved on the blade's secondary bevel.
If you need a summary comparison chart, a great source is the Grand Logarithmic Grit Chart from www.gritomatic.com.
In addition to the differences in industry standards and grit classifications of abrasive material, there is another important technological aspect that affects the understanding of grit as such.
It is commonly believed that abrasives are divided into water, diamond, and oil sharpening stones. This division is only partially true when it comes to the use of cutting fluids.
In fact, abrasive stones should be divided according to the origin of the abrasive grain, particles, or whatever you want to call them. Thus, according to the origin and formation of the abrasive grain, all sharpening stones are divided into two groups:
There are certain categories and classifications among natural stones. Considering that stones are created by nature, the fractions of the same abrasive may not only have different sizes, but the stone may have different kinds of inclusions from other rocks. Hence it is often very difficult to assign a value to a certain natural stone on the grit scale without first testing it.
Natural stones, as strange as it may seem, can be used with both water and oil.
Often, some natural stones have a completely different effect on the cutting edge than synthetic abrasives. An example would be Japanese natural slates, which have a structure of thin flakes, which remove the metal in a different way and their grit size is much higher than what is written on them and many times better than synthetic abrasives.
Synthetic abrasives produced by the chemical industry can have a much more controlled and predictable particle size. The grit size of a synthetic abrasive stone, as written on the package, is well within established technical norms.
However, it is also possible to use water and oil as coolants. In addition, some abrasives, such as diamonds and silicon-carbide-based stones, can be used without any coolant, but this is not entirely correct.
The grit size of any stone is certainly an important factor in the choice of abrasives, but the choice of the coolant used with the stone is an essential part of the decision.
For carbon blades that are prone to rusting, we recommend the use of oil stones or abrasives, such as diamonds, that do not require the use of coolants.
When sharpening stainless steel or steels that have some level of corrosion protection, water-type sharpening stones can be used. In addition, sharpening with water is not just fast, but it often gives a higher sharpness due to the lower density of the cooling liquid.
Because of their many performance advantages, water stones have become very popular. A whetstone can be made of both natural and synthetic materials. However, the vast majority of water stones are synthetic, so we will focus on them.
Water stones are often made of the abrasive material aluminum oxide, but there are exceptions.
The difference between a water stone and an oil stone is in their bonding agent, which traps the abrasive material. Water stones have a softer bond than oil stones. The softer bond allows faster metal removal because the abrasive particles get refreshed more quickly.
The high abrasive grit renewal rate is a definite advantage of water stones. Water stones are also available in a much wider range of grit sizes than most other stones. Water stones are available in grit sizes up to 120 grit and are easily found in grit sizes even above 8000 grit (the finest being 300000 grit).
Another obvious advantage is the use of water rather than oil to remove metal particles from the surface of the stone when you sharpen a knife. Water is almost always at hand, and water dirt is easier to clean.
The relatively low density of synthetic water stones also has a disadvantage. While working with the stone, the surface may develop a depression, and the stone must be occasionally leveled, which is a topic for another article.
Oil stones are the traditional stones that many generations of sharpeners have used to sharpen knives. In comparison to a whetstone, oil stones are harder. They are made of one of three materials: novaculite, aluminum oxide, or silicon carbide. These stones are used with oil as a coolant which prevents the stones from getting clogged.
The original traditional oil stones are natural Novaculite stones. These stones are divided into different grades according to their density and the quality of the blade finishing.
Aluminum oxide oil stones are very popular in the sharpening community. This type of stone can remove metal quickly and create a fine and aggressive edge on tools and knives. The grading system of these stones usually distinguishes between fine, medium, and coarse grit.
The most effective metal-removing oil stones are made from silicon carbide. Thanks to their quick-renewing capability, they are well-suited for the initial roughing of dull blades.
For all their advantages, oil stones with a good overall performance and low price have one disadvantage compared to all other types of abrasives. The metal-removal rate of these stones is the slowest because the grit is renewed slowly and the presence of oil also slows down both the sharpening and the cleaning processes of the stones from metal particles.
Quite often, in fact, average users or even sharpeners use sharpening stones without any coolants and include diamond sharpening stones and diamond bars in this category. Technically, this is a misconception and is fundamentally wrong. Even the use of the word "stone" here is extremely inappropriate, as there is no and cannot be any connection with a real stone. A large diamond-based sharpening stone can only resemble a natural stone in size. It can also have a second side suitable for sharpening as well. That is where its resemblance ends.
Abrasives based on diamonds or elbors (CBN) can be used without a coolant in one particular case - when the abrasive is made with a galvanic or a copper-tin bonding agent.
In all other cases, that is, when you use abrasives based on other bonds, the use of a coolant is not just a recommendation, it is a must!
In conclusion, we recommend to all beginners not to neglect the use of roughing stones, as they greatly speed up the sharpening process. With this approach, it is important to understand that the sharpening process consists of the roughing, main sharpening, and finishing stages to maximize the retention of sharpness.
So, choose the more versatile sharpening stones that will cover most of your needs, will handle your knife steel, fit your budget, and are easy to use and maintain.
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