Grindstone
Grinding stones are flat, angular or round to oval tools made of crystalline material with a flat work surface. They are used for grinding and smoothing. As with the millstones , it is important that the work surface is as flat but rough as possible. Plate-like basic forms made of sedimentary rock such as sandstone and slate , but also basalts , granites and quartzites are suitable as natural grinding stones, and broken grinding stones were also used.
prehistory
In the Lower Palaeolithic sporadically, in the Upper Paleolithic and Mesolithic increasingly served grinders especially for smoothing of wood, horn and bone tools. In the Neolithic, grinded and polished hatchets, axes and chisels are characteristic and whetstones often have several grinding tracks (grooves) that may have been pre-formed by picking. This is the difference to the downstream (of millstones). They were used for smoothing wooden, horn and bone implements and for rounding and calibrating (making the outer diameter) of beads made from various materials. A grindstone comes from the Hohler Fels cave , the size of which could have been used to grind bone needles . Whetstones in pairs with a groove were probably used to smooth wooden arrow shafts.
history
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A grindstone (from Middle High German slīfstein ) is a mostly elongated stone the size of a palm or a hand for sharpening cutting tools or for shaping precious stones. Grinding stones are made from different materials: natural stones for grinding purposes are mined all over the world. Are known z. B. those from Arkansas / Ouashita Mountains, Belgium (Ardennes) or the French Pyrenees. Artificial stones can consist of various abrasive materials (see under 'Synthetic sharpening stones').
Grinding stones for rotating tools are known as grinding wheels or wheels. Because of the high circumferential speed that can be achieved, frictional heat arises on the workpiece. For sensitive materials, e.g. B. hardened knife and tool blades, care must be taken to cool with liquid so that the steel does not lose its hardness, which is the case at temperatures above 170 ° C. The thin edges of knife blades are particularly vulnerable here.
The professions of whetstone cutter and whetstone turner dealt with the production of whetstones. See also → millstone
Traditional production of round whetstones in technical terms
Round grindstones were hand-picked from quarries in Germany until the 1970s. B. in Neidenbach , a traditional place of production in the Eifel . The place of use was mostly the knife and scissors production in the Bergisches Land, especially Solingen and Remscheid .
The maximum diameter of the grinding stones was 3.04 meters due to the rail gauge. The stone cutter, called a grinder, struck a circular, foot-wide ring out of the rock with a rough cutting tool, the hammer, which looked like a pickaxe. The broken rock was shoveled away with a narrow scrap chop. After the still raw round had been cut, mostly 42-48 wedges were slowly hammered in at the bottom of the still solid rock, in the desired thickness of the grindstone, around the entire circumference by two grinders. A third stonemason, standing on the later grindstone, checked how the wedge crack pulls. The wedges were “pulled” by light driving blows until the grindstone “tears” out of the rock, the so-called bearing.
After tearing through, long iron levers, so-called hoists, 2.35 meters long and 35 kilograms were used by hand to lift the stone out of the warehouse with the slightly angled claws. Wide wooden wedges were placed underneath, in technical terminology. With a compass, a round stone disk and the "straight edge (a long, straight wooden slat), the top is compassed" that is, measured and "seen" in order to determine the most favorable surface section, taking into account the unevenness. A pointer is used to measure the excess stone material, which must then be "removed" in order to obtain a level surface. The aim is to have to remove as little material as possible after seeing.
With a hammer and the Klepper, a wide, round wooden hammer, the future real curve of the stone is provisionally hammered into the upper edge. From this upper edge, the final thickness of the round body is determined and the surface is leveled by the shotguns with the shot hammers from the outside to the inside, muffled in technical jargon or roughly removed. The depressions in the rough surface, which serve as an orientation for the future thickness, are called peasants, the protruding rock that has to be broken is called bosses or humps. The shredding was done on the same day, as the fresh or green stone was still soft and not brittle due to the moisture bound in the stone.
Then an angle iron is set for the final edge and the circular line is marked with a hammer. Then the so-called path is hewn finer and sharpened at the correct angle.
Due to the speed of the stones from 14 to 18 m / s, the processing of unbalances was very important. With so-called wolf teeth, up to eight finger-thick and pencil-long steel rods that were lined up in a tool, the surface of the stone was further refined and rough traces of work were sharpened. The surface, the so-called wreath, was seen again with the compass to identify bumps so that the surface is even smoother.
After one side of the stone had been processed, it had to be turned over while still lying on wedges in the warehouse. With up to three stone winches, each of which could lift around 100 quintals (5 tons), the stone was slowly erected on wooden beams. The so-called building was erected in the direction of fall. The construction is two piles of large, uneven chunks that catch the stone. The height of the piled stones or scraps are designed so that the upper two thirds of the stones are smashed on impact and the weight of the falling grindstone is absorbed.
After turning, you can see the lower surface, which also has to be leveled. Most of the time, the underside had a distinct bulge or so-called belly, which is removed with wedges. At the defined boundary line, wedge holes are driven, wedges are attached and driven in. Since the wedge cracks always go to the thinnest point in the rock, there is no risk of damaging the round. Then the process of smoothing the surface is repeated, and the surface is fattened with the shot hammers and wolfe irons until the stone has obtained its final surface and angularity.
Health hazard
At the time of early industrialization , grinding was arduous work. The "grinder disease" - caused by the metal and stone dust, lying on the chest in front of the grindstone and poor ventilation - often led to the early death of the workers. The crystalline silica contained in the fine quartz dust led to the dreaded silicosis . At the time of the Schleifkotten or Bachkotten, this disease was seen as inevitable and the early death of the Schleifer was almost taken for granted. Dry grinders were on average barely 35 years old, wet grinders rarely over 45 years old. This was accepted as regrettable, but normal and apparently unalterable, and it was centuries before the authorities began to see the need for action.
Friedrich Engels described the "grinding diseases" in 1844/45 in his treatise The Situation of the Working Class in England. According to his own view and authentic sources and also went into the situation of the grinder in Sheffield , the northern English city was in the middle of the 19th century leading in the production of high-quality abrasive goods even before Solingen .
Types of sharpening agents
Sharpening stones can be classified as follows:
Synthetic sharpening stones
Synthetic whetstones with a plastic bond usually have a soft, open-pore structure with homogeneous particle storage, they grind quickly, but also wear out quickly. In the event of improper handling, there is the possibility of cutting into the stone, which is neither beneficial for the stone nor the blade. Most of these stones were developed for sharpening Japanese knife blades, which have a different geometry than western knives. They do a good job there, but when used to grind a secondary cutting bevel they quickly become hollow and then have to be dressed. Ceramic-bonded waterstones with particularly high wear resistance for professional use are constantly being further developed in cooperation with industrial customers from the metal sector. Otherwise ceramic whetstones are standard and suitable for many grinding tasks. They are also available as discs, bench stones, files or ceramic rods, which are useful for some applications.
The abrasive media that are used are
- Corundum (aluminum oxide Al 2 O 3 ) used to come from natural sources (e.g. Naxos island, Greece). It is a very hard mineral that is now artificially produced for abrasives. Various degrees of purity can be achieved during production using the melting process: from dark brown normal corundum to white high-grade corundum. In order to influence the properties (e.g. toughness, splinterability) of the high-grade corundum in the desired manner, certain elements such as chrome or zirconium are incorporated into the crystal lattice in a controlled manner and the different types of high-grade corundum with the corresponding colors are created.
- Other oxide ceramics as well as non-oxide ceramics are of great importance as cutting materials in machining, but not for household applications.
- Diamond is suitable for the highest demands on the removal of even the hardest materials and precision. Today there are many qualities of man-made diamonds in addition to natural ones.
- Silicon carbide (SiC) is an artificial crystal with very similar properties to diamond. The purer green SiC, extremely hard and splintering with sharp edges, and the dark SiC, which is somewhat tougher, blockier and more stable, are used.
The quality of whetstones is determined by their content of abrasive substances, their quality, the even distribution of the abrasive grains in the matrix and the type of bond that on the one hand has to hold the individual abrasive grain in place, but on the other hand it breaks when it is worn out to make way for new, sharper abrasive grains. The abrasive media can be of very different quality and effectiveness, which determines their price.
For the grinding stones, the grains are often mixed in a targeted manner in order to obtain a cutting and a supporting grain and thus to increase the service life of the abrasives.
Natural water stones
Japanese natural stones as well as Belgian chunks or the Slovakian Rozsutec are sedimentary or limestone with embedded corundum, oxides, quartzites or semi-precious stones (e.g. garnets). The structures and the homogeneity of these stones can vary depending on the mining site and location.
Also mica schist , often with quartz deposits , such as B. the Norwegian stone from the Eidsborg grinding quarry and phyllite (stones from Wästilä / Finland) were mined and were in great demand. Many natural grindstone deposits are becoming increasingly scarce - sometimes after centuries of mining.
Natural stones can vary greatly in quality and structure, which require careful examination of the stones. However, they generally have the advantage that they do not have to be soaked for a long time with water or oil. Moistening is sufficient in most cases, which enables quick use.
Oil stones
The old expression oil stone comes from the time when there were no stainless steels. Knife blades that were ground or honed on a stone with oil were given a light film of oil during this process and thus a short-term rust protection. Since some stones - especially the first artificial stones with synthetic resin bond - could not be used with grinding oil and would decompose, oil-resistant stones were particularly popular.
The Arkansas stones are dense and wear-resistant novaculite . They are well suited for honing carving and turning tools. Stripping is the process of applying the last fine sharpness to an already well-sharpened cutting tool.
The natural Arkansas stone comes in many different qualities and colors. Pure white, somewhat porous soft Arkansas stones are particularly valuable, but they can no longer be found. The transparent, gray and black Hart Arkansas variants are used with either low-viscosity grinding oil, petroleum or lamp oil. The stone does not absorb the liquid, so a few drops are sufficient. When used dry, the stone clogs immediately; it does not work with water.
All Arkansas stones must be rubbed with a fine silicon carbide stone before use, or with another piece of Arkansas. To do this, the stone is carefully cleaned and then rubbed with water (not oil!). This process creates a matt, non-reflective surface. An Arkansas with a glossy surface has no abrasive effect.
The somewhat coarser and mostly more colored Ouashita stone (also known as Washita) comes from a neighboring deposit with a similar composition.
General advice: Whetstones that have been impregnated with oil once no longer absorb water. Therefore, when you first start using a stone, it is important to examine it for porosity. Stones that are very dense and hardly absorb liquid usually work well with petroleum.
Porous grindstones that have absorbed oil can usually be regenerated by boiling them in water with the sparing use of a non-moisturizing dish soap or detergent.
Diamond stones
With these sharpening media, the diamond powder, which is effective for grinding, is applied as a thin layer to a metal base in a galvanic nickel matrix. The diamond plates ensure high flatness, durability and effectiveness on condition that the diamonds are of high quality (monocrystalline).
Carpenter's grindstone
Whetstone for turning
Black arkansas stone
application
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With the exception of the stones made from diamond dust and the ceramic rods, it is necessary to wet the whetstone with water or petroleum / grinding oil while grinding. This measure ensures, among other things, that no metal abrasion can deposit in the pores of the stone and that it grinds more effectively. On such a prepared stone z. B. a knife blade laid flat and the back slightly raised depending on the desired grinding angle. This angle depends on the geometry and the area of application of the knife. Fine cutting edges (found on scalpels, kitchen knives and carving knives) require a small angle of 15 to 20 °. At a smaller angle, the cutting edge becomes sharper, but also more sensitive. Then the cutting edge is pulled along the stone with an arched movement and with light pressure from the base of the handle to the tip. This continues until a ridge is formed. This is repeated with the other side of the blade. If a ridge has formed here too, you switch to a stone with a finer grain. This stone is used to grind at a slightly increased angle. As before, you always work with the ridge down towards the stone until the ridge changes to the other side. Then switch sides and continue applying less pressure until the burr is removed.
The water tank of a rotating grindstone must be emptied after use. This prevents only part of the stone from remaining in the water while the rest of the stone falls dry. The partial impregnation of the stone leads to imbalance and one-sided wear.
See also
literature
- John Juranich et al: The Razor Edge Book of Sharpening. Warner Books, New York NY 1985, ISBN 0-446-38002-4 .
- Jim Kingshott: Sharpening. Pocket reference book. Techniques & equipment. Guild of Master Craftsman Publications Ltd., Lewes 1996, ISBN 1-86108-007-7 .
- Leonard Lee: The Complete Guide to Sharpening. The Taunton Press Inc., Newtown CT 1995, ISBN 1-56158-125-9 .
- Joachim Hahn : Recognition and determination of stone and bone artifacts. Introduction to artifact morphology (= Archaeologica Venatoria. Vol. 10). 2nd Edition. Verlag Archaeologica Venatoria et al., Tübingen 1993, ISBN 3-921618-31-2 .
Web links
Individual evidence
- ↑ Documentary - Making a grindstone in the sandstone pit Chr. Hort , LVR Institute for Regional Studies and Regional History
- ^ Friedrich Engels: The situation of the working class in England - according to their own views and authentic sources, Leipzig 1845.
- ↑ See: Helmut Beermann: Messer + Klingen. A journey through five centuries of blade manufacture. Solingen: Martor , 1993. page 86