Why are there different grit sizes?
The different grit sizes of the sharpening units for our knife sharpeners are necessary because the sharpening process takes place in several steps. Depending on the condition of the knife blade, 2-4 steps are necessary. The blade is processed with increasingly finer grits from step to step.
The coarser grits are used to remove scratches and even out cracks and unevenness. This removes enough material to make the cutting edge smooth again.
Finer grits smooth and refine the cutting edge until the desired sharpness and smoothness is achieved. How to check whether this has been achieved is described below.
The correct choice of grit for each step is critical to the life and cutting performance of the blade and its suitability for specific tasks. The grit of the sharpening unit or whetstones determines how coarse or fine the abrasive particles are, which in turn influences the material removal and therefore the sharpness of the knife blade
Coarser grits naturally remove more material, but are less suitable for fine grinding. Fine grits, on the other hand, ensure a precise, smooth grind but remove very little material.
International standards such as FEPA or JIS provide guidance.
What do FEPA and JIS stand for?
FEPA is the abbreviation for "Fédération Européenne des Fabricants de Produits Abrasifs" (European Federation of Manufacturers of Abrasives). FEPA is a European organisation that sets standards for abrasives, including the classification of grit sizes for abrasive stones and abrasive papers.
There is FEPA P for paper and FEPA F for abrasive grits, which is still the standard that is or should be labelled on all abrasives.
JIS stands for Japanese Industrial Standards. These standards are developed and set by the Japanese Standards Association (JSA) and comprise various industrial standards, including specifications for abrasives such as whetstones and their grit sizes. As japanese kitchen knives are becoming increasingly popular in Europe, this standard is also increasingly specified for grit sizes.
In summary, both FEPA and JIS provide standardisation to ensure that abrasives are consistent and reliable in their performance. This is particularly important for precision work where choosing the right grit is critical to the end result. These standards also provide guidance to manufacturers and users when selecting the appropriate abrasive for specific applications.
Our sanding units use the FEPA F values. If you are more familiar with the JIS scale, you will find a small overview table here.
| FEPA-F | JIS |
|---|---|
| 2000 | 8000 |
| 1500 | 6000 |
| 1000 | 3000 |
| 800 | 2000 |
| 600 | 1200 |
| 500 | 800 |
| 320 | 400 |
| 280 | 320 |
What influence does the steel grade have on the choice of grit?
Harder steels with a high Rockwell hardness (HRC) often require coarser grits, especially in the initial grinding steps. The reason for this is that harder materials are more difficult to machine and a coarser grit can remove more material, which increases efficiency and therefore significantly reduces the grinding time.
Finer grits can wear faster on hard materials as the small abrasive particles are worn down more quickly. It is therefore important to choose the right hardness and quality of abrasive to meet the requirements. For this reason, Warthog Sharpeners only uses diamond- and ceramic grinding units.
Softer steel grades with low Rockwell hardness are easier to grind and often require a finer grit to achieve a smooth finish and avoid over-finishing. If the grit is too coarse, there is a risk of removing too much material or even damaging the surface. In this case, reworking is necessary, which in turn shortens the service life of the blade.
Fine grits minimise the risk of burr formation on soft materials, which can be caused by abrasives that are too coarse.
Which grit is ideal for knife sharpening?
In contrast to the exact selection of the right grinding angle, choosing the right grit is not quite as simple.
The image of a blunt knife that crushes a tomato more than it cuts it is widespread. But it is more than an image. It is a clear sign that the knife urgently needs sharpening. After all, it is frustrating when a blunt knife no longer cuts properly or a damaged blade shreds vegetables, fruit, meat and fish.
Choosing the right grit for the type of steel and the condition of the blade is crucial for an optimum sharpening result. Material removal should be as low as possible to maximise the service life of the blade. At the same time, you don't want to have to sharpen forever to compensate for damage. And you still want to end up with a cutting edge that is as sharp as possible.
Finding a good balance here is therefore essential.
Which grit is ideal for knife sharpening?
Step 1:
Repair with coarse grit (up to 300)
These coarse grits remove a lot of material and are therefore used to repair badly damaged or worn blades. They are useful for removing burrs or nicks in the cutting edge. And they can even be used to create a new cutting edge shape or greatly modify the cutting edge.
Typical usage
- First step in sharpening badly damaged knives.
- Creating or adapting the cutting edge shape.
Step 2:
Basic grinding with medium grit (300 - 600)
These grits are ideal for sharpening knives that only require a moderate degree of sharpness. They help to create a sharper edge after the knife has been repaired with a coarse grit.
Typical usage
- Everyday maintenance and regular sharpening.
- Preparation step for polishing.
Step 3:
Fine sharpening with fine grit (600 - 1000)
These grits are intended for fine grinding, where a sharp but not reflective cutting edge is to be achieved. They are used to further increase the sharpness of the blade. In most cases, a grit of 1000 is more than sufficient to achieve an excellent result.
Typical usage
- Finishing of blades that require a high degree of sharpness, such as chef's knives.
- Penultimate step before final polishing.
Step 4:
Polishing with very fine grit (over 1000)
Very fine grits are used to polish the cutting edge to achieve extremely sharp and smooth, mirror-like surfaces. These grits remove the fine burr that forms during sharpening. In our grinding units, this step is performed by the finishing sides.
Typical usage
- Final polishing of high-quality knives and razors.
- For precision work that requires an extremely sharp edge.
Test 1:
Visual test
Blades that are particularly blunt or damaged can be easily recognised with the naked eye. If the blade has not been resharpened, it may have become visually blunt after prolonged use.
Rough damage, on the other hand, may have been caused by improper use or simply by an accident. The knife may have been dropped or jammed during use.
In the case of visible damage, a low grit size of max. 300 should be used so that the damage can be repaired quickly.
Test 2:
Reflection test
The bluntness of the knife blade can also be checked using light. To do this, hold the knife with the cutting edge facing upwards under a lamp (a lamp on a smartphone is sufficient). Then look at the cutting edge, not the bevelled edge.
With sharp knives, no reflections can be seen directly on the cutting edge. With blunt knives that do not have any major damage, on the other hand, you can see a continuous narrow line of reflection.
In this case, a grit between 300 and 600 is recommended and the knife is ground with this grit until the reflection has disappeared.
Test 3:
Ballpoint pen test / nail test
In the ballpoint pen test or nail test, hold the biros or thumbnail at an angle of approx. 45 to 60 degrees and carefully apply the blade without applying pressure. If the blade sticks, it is sharp. If, on the other hand, it slips under its own weight, it needs to be sharpened.
In this case, it is advisable to use a grit of 600 to 1000. The blade must be sharpened until it sticks to the biros or thumbnail and no longer slips over it.
Test 4:
Paper test
The paper test is a very popular way of testing a knife blade, as you can immediately get a good impression of whether the cutting edge is sharp throughout. It's also fun to cut through something as unstable as a sheet of paper with a sharp blade.
For this test, take a sheet of paper vertically in your hand and try to cut through it from top to bottom with the knife. With a well-sharpened knife, this can be done easily and, above all, evenly.
If the sheet cannot be cut through evenly, it must be sharpened with a grit of 600-1000 until the knife glides through the sheet of paper. If the knife even gets stuck, there is probably still rough damage to the cutting edge and you have probably skipped the first sharpening step.
Test 5:
Tomato test
The tomato test is more of a real practical test, as the tomato will probably be eaten afterwards.
Due to the smooth, tough skin and soft flesh, the tomato can quickly be crushed with a blunt blade, as the blade cannot cut through the skin. Or the blade simply slips off the skin.
A sharp blade, on the other hand, has no problems with the skin, even with light pressure, and the tomato can be cut into thin slices without any problems.
If necessary, the knife must be carefully resharpened with a grit of 1000 or more until nice thin slices of tomato can be cut.
Summarised overview table of grit sizes
| Grit size | FEPA F | JIS | Usage |
|---|---|---|---|
| Coarse | Up to 300 | Up to 500 | These grit sizes are used for pre-grinding very blunt cutting edges or for repairing damaged cutting edges. The material removal is high, so that even new cutting edge shapes can be achieved. |
| Medium coarse | 300-500 | 500 - 1000 | These grits are used to refine the cutting edge and achieve a medium sharpness. They are ideal for regular resharpening. |
| Fine | 500 - 1000 | 1000 - 3000 | These grits are used to repair minor imperfections. They also serve as preparation for the polishing phase. |
| Very fine | From 1000 | From 3000 | These grits are intended for polishing blades. They can be used to achieve extremely sharp edges. This is usually the final stage of the grinding process. |
Our grinding units for every blade
