A grinder is one of the first grinding machines known to man. It has been technically displaced by the roller mill ( roller mill ).
The original form consists of two millstones that the grinding material crushing. The lower stone, the floor stone, is fixed, while the one above, the runner or runner stone, is driven by the stone spindle via a mill iron . These two stones are framed by a wooden chest surrounding them. The pouring funnel is placed on the chute cover plate, including the vibrating shoe, which is made to vibrate by a three or four stroke (also three / four click) on the spindle axis depending on the rotor stone speed, so that the corresponding amount of grain from the funnel through the stone in the upper stone attached grinding lye (also: stone eye) is supplied. This shaking of the vibrating shoe also causes the "rattling of the mill". The ground material gets centrally between the stones with the help of the "gulp" - a cavity in the grinding stones lying on top of one another, which favors the supply of ground material. The two millstones float on top of each other with a small gap. The gap distance is variable via the lifting tool (lever) or spindle and is set smaller than the diameter of the ground material. Ideally, the stones do not touch. Due to the rotational movement of the upper stone and the “stone sharpness” applied to it, the grist is cut and ground (less squashed). It falls out of the millstone gap outside,is collected in the grinding vat surrounding the stones and discharged via a bagging nozzle. The vat also serves to encapsulate the grinding process in order to hold back the resulting dust and moisture and to isolate it from environmental influences. In addition, the vat guides the resulting grist into the bagging nozzle set up for this purpose.
It is important that the grinding process runs as smoothly as possible, from the feeding of the ground material through the feed device to the uniform rotation of the rotor to good ventilation of the grinding process in order to dissipate moisture and heat. The constant rotation is the main challenge with windmills , since the wind only provides irregular energy .
Since the husks of spelled , unlike wheat , are firmly fused with the grain, it must be peeled off before grinding. In the past, a "tanning tunnel" was used for this purpose. This is a grinding process in which the distance between the stones has been chosen so that the grain has not already been crushed.
The stones must be equally hard and sharply porous. They achieve this through the property of breaking minerally as sharp as possible; a kind of self-sharpening, the grinding surface must remain rough. The stones can be put together from several stone lumps, the higher qualities are from one piece.
- French : freshwater quartz . Highest quality, mostly found in La Ferté-sous-Jouarre , France , hence also champagne stone, used for the highest quality flour.
- Jonsdorf sandstone : In the millstone quarries of Jonsdorf (Saxony), very high quality millstones were quarried. The sandstone in this area was hardened (fritted) by volcanic influence and shows a similarly good grinding quality as the French stones.
- Porphyry and granite : hard and very porous, for high quality.
- Blauer or German : Porous basalt lava , for medium qualities. In the quarries in the Mendig and Mayen area , millstones from tephrite lava have been produced since the Middle Ages, sometimes even in prehistoric and Roman times .
- Sandstones : Hard sandstones, low quality; only used for fodder crushing due to more or less severe abrasion.
- Artificial stones : Artificially constructed stones, produced from the beginning of the 20th century, can be used on all sides.
- Mill sandstone : Locally occurring, high-quality fine-grain and silicified sandstone for all types of grinding (including paint, plaster or glaze mills and others) from the millstone pits near Waldshut.
- Verrucano : Millstones have been made on the Castels hill in Mels , Switzerland since the Neolithic Age. At the end of the 19th century they were bought by German stone lords and exported from Germany to Africa.
- Nagelfluh conglomerate was also used for millstones.
Millstones of the mill Britz without Mahlbütte
Millstones of the cap windmill in the museum village of Cloppenburg
- Alain Belmont, Fritz Mangartz (ed.): Millstone quarries: Research and valorisation of a cultural heritage of European industry [antiquity - 21st century] . (= Römisch-Germanisches Zentralmuseum Mainz - Conferences, Volume 2). Schnell und Steiner publishing house, Regensburg 2007, ISBN 978-3-7954-2012-3 .
- Klaus Schmidt, CJB Karsten (ed.): The millstone quarries between Mayen and the Laacher See / by the mountain master Schulze zu Düren. Copy from Archives for Mining and Metallurgy. Tape. 17, Berlin 1828, reprint, Görres, Koblenz 2000, ISBN 3-920388-85-2 .
- Torsten Rüdinger, Philipp Oppermann: Small mill knowledge - German technical history from the friction stone to the industrial mill . terra press, Berlin 2012 (2nd edition), ISBN 978-3981162677 .
- Gerald Bost: The millstone quarries in Jonsdorf . Der Mühlstein, born in 2001, issue 4.77
- Harald Marschner: The Perger millstone industry . Molina, born 2018, terra press, Berlin
- Charles D. Hockensmith: The Millstone Industry: A Summary of Research on Quarries and Producers in the United States, Europe and Elsewhere . McFarland & Company, Inc. Jefferson, North Carolina, ISBN 978-0-7864-3860-0 , 2009
- Alexander Konschak: A mill quarry on Heideberg near Zittau . Verlag Gunter Oettel, Bad Muskau 1996. ISBN 3-980 4900-2-5