Grinding stones
Grinding stones
EXPERT KNOWLEDGE GRINDING STONES
Nothing works without sharp tools!
The best cutting tool is of little use if it is not properly sharp. Opinions on how to turn a cutting edge from blunt to sharp often differ widely, even among experts.
The art of sharpening with whetstones has a long tradition and dates back to ancient times. In Japan, where sharpening became a highly respected craft, special sharpening techniques and corresponding whetstones were developed to perfect the valuable hand-forged blades.
Sharpening on Japanese waterstones
This method is equally suitable for knives and tools and has the following advantages:
- The hardness and edge retention of the steel are not affected as no heat is generated.
- Thanks to the wide range of grit sizes available, any number of fine cutting edges can be achieved.
- As whetstones are rigid by nature, exact cutting edge geometries can be produced (no rounded bevelled surfaces as with felt or rubber discs).
- No danger of flying sparks.
- The basic equipment is not complex.
The achievable sharpness depends on the following factors:
- On the molecular structure of the steel, i.e. the fine grain and hardness of the blade steel: the finer/harder the steel, the sharper.
- The geometry of the cutting edge: the smaller the cutting angle, the lower the cutting resistance.
- The fine grain of the stones: the finer the grain of the whetstone, the sharper the edge.
How are sharpeners differentiated?
Sharpening tools are generally divided into four groups:
- Roughing stone (grit 100-500):
Coarse-grained whetstone for high material removal, e.g. repairs, chipping, correcting the grinding angle. - Sharpening stone (600-3000 grit):
Medium-grit whetstone for sharpening blunt cutting edges. - Honing stone (4000-6000 grit):
Fine-grained whetstone for honing after sharpening. - Polishing stone (grit 8000-10 000, rarely up to 30 000):
Grinding stone with the finest grit for honing and polishing.
Further distinguishing features are
- Purity of the grit:
The more uniform (pure) the grit, the better the sanding result. Mixed grits or non-pure grits always result in reduced grinding behaviour. - For which steels:
For low-alloy carbon steels, such as Japanese chisels and plane irons, knives with centre layers made of white and blue paper steel as well as axes and hatchets. For high-alloy steels, such as Western chisels and plane irons, knives with centre layers made of powder metallurgical steels or stainless steels, e.g. VG-10 steel and sculpting irons from Pfeil. - Size of the grinding surface:
The grinding surface should always be adapted to the tool to be ground. As a rule, the bigger the better. The grinding surfaces of common whetstones vary depending on the model and manufacturer. However, typical sizes range from 70 x 200 mm to 80 x 250 mm for standard whetstones, which offer a good balance between size and handling and are suitable for most knives and tools. These sizes offer sufficient space for precise guidance and also make it possible to sharpen a longer blade evenly.
To get started, we recommend one sharpening stone and one honing stone or a combination stone.
Types of whetstones
The available whetstones can be categorised as follows:
- Synthetic waterstones with a synthetic resin bond:
These popular stones have an open-pored structure with homogeneous particle embedding and surface. They grind quickly, but should be regularly dressed when worn. Stones with a synthetic resin bond must be soaked in water before use. - Synthetic waterstones with a ceramic bond:
Grinding stones with a ceramic bond remain flat for longer and can be used immediately after being wetted with water. (Splash and Go)
You can find the bond type of each stone in our shop under the measurement data/attributes.
Synthetic waterstones in the shop
- Natural stones
Japanese natural stones, as well as Belgian chunks or the Slovakian Rozsutec, are sedimentary or limestone rocks with embedded corundum, oxides, quartzites or semi-precious stones (e.g. garnets). Due to their slightly inhomogeneous structure, they harmonise particularly well with hand-forged steels.
Natural waterstones in the shop
- Oilstones
Arkansas oilstones (natural stone) are very dense and wear-resistant Novakulite. Synthetic oil stones are also available. Both are soaked or rubbed with oil before sharpening. Due to their hardness, they are well suited for honing carving tools, which often have small blade cross-sections and wear out sharpening stones quickly.
Oil stones
in the shop
- Diamond stones
In these sharpeners, the abrasive diamond granulate is applied in a nickel matrix as a thin layer on a metal base. They guarantee fast material removal as well as high flatness and durability, provided that the diamonds are of high quality (monocrystalline).
Note:
Do not combine oil and waterstones, as oil reduces the effect of waterstones.
Avoid cheap products, which are usually made with (short-lived) polycrystalline diamond dust.
Care/storage of resin-bonded waterstones
Some water stones must be soaked before use, e.g. King. The following care/storage is recommended to keep these stones ready for use at all times:
- For storage, it is best to use a sealable plastic tub in which the stones can be permanently stored in a water bath.
- To prevent the formation of algae, you can add a splash of vinegar or disinfectant to the storage water (harsh household cleaners can attack the bond of the stone).
- Never expose the stones to frost, risk of cracking!
- If the water has a high lime content, frequent drying out should be avoided as the stones will otherwise become clogged and lose their effectiveness.
- Treat the stones with care. Keep them flat, clean and oil-free (oil prevents water absorption and reduces the grinding effect).
Dressing the whetstones
Many Japanese waterstones have a rather soft, open-pored bond, which constantly releases fresh abrasive particles during sharpening and thus enables a high level of effectiveness. The resulting wear requires regular dressing of the waterstones. The stones usually need to be soaked in water before use.
A ceramic whetstone (splash and go), on the other hand, has a very hard bond and little wear. It needs to be dressed less often. However, in order to achieve good sharpening performance, the manufacturer must use very high-quality and wear-resistant abrasive particles. This is why such stones are usually more expensive.
In extreme cases where the bond of the abrasive particles is completely rigid and the stone is therefore virtually wear-free, diamonds are used as abrasive particles (DMT).
Dressing of water stones
For tools with a straight cutting edge, it is particularly important that the stones used are absolutely flat and at an angle. Check the flatness of the stones using a straight edge (no. 707290) using the light splitting method. If the stone is hollow or round, it must be levelled. There are various methods for this. The simplest method is to use a diamond dressing block (No. 705429 or No. 711613). The well-watered stone is rubbed in a circular motion on the dressing block until the surface is even. Light-coloured areas indicate areas that have already been worn down, while darker areas have not yet been in contact. Continue sanding until a continuous light-coloured surface is visible and rinse off the sanding paste regularly.
Alternatively, the dressing set (no. 711115) can be used by placing 100 grit water-based sandpaper on a flat granite stone slab. A sharpening stone dressing grid (No. 711297) fulfils a similar function.
Dressing of oil stones
Tip:
When dressing several whetstones with different grit sizes, you should always work from the finest stone with the highest grit size to the coarsest stone with the lowest grit size. This sequence prevents any remaining abrasive particles on the dressing block from scratching the surface of a finer stone. Rinse the dressing block briefly and thoroughly under running water after each sanding process.
It is worth investing in high-quality whetstones that are characterised by their wear resistance and durability. You are guaranteed to find the right stone to meet your individual needs and requirements from the wide range of tried-and-tested and carefully selected whetstones at DICTUM. Quality pays off, especially when it comes to precise and sustainable sharpening of your high-quality knives and tools.
