Grindstone (tool)

Grindstone (tool)

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Encyclopedia
A grindstone is a round sharpening stone
Sharpening stone
Sharpening stones, water stones or whetstones are used to grind and hone the edges of steel tools and implements. Examples of items that may be sharpened with a sharpening stone include scissors, scythes, knives, razors and tools such as chisels, hand scrapers and plane blades...

 used for grinding
Grinding (abrasive cutting)
Grinding is an abrasive machining process that uses a grinding wheel as the cutting tool.A wide variety of machines are used for grinding:* Hand-cranked knife-sharpening stones * Handheld power tools such as angle grinders and die grinders...

 or sharpening
Sharpening
Sharpening is the process of creating or refining a sharp edge of appropriate shape on a tool or implement designed for cutting. Sharpening is done by grinding away material on the implement with an abrasive substance harder than the material of the implement, followed sometimes by processes to...

 ferrous
Ferrous
Ferrous , in chemistry, indicates a divalent iron compound , as opposed to ferric, which indicates a trivalent iron compound ....

 tool
Tool
A tool is a device that can be used to produce an item or achieve a task, but that is not consumed in the process. Informally the word is also used to describe a procedure or process with a specific purpose. Tools that are used in particular fields or activities may have different designations such...

s. They are usually made from sandstone
Sandstone
Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...

.

Grindstone machines usually have pedals in which to speed and slow the stone to sharpen metal
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...

 to the point of perfection.

A rotary grindstone − the earliest representation thereof, which is operated by a crank handle, is shown in the Carolingian manuscript Utrecht Psalter
Utrecht Psalter
The Utrecht Psalter is a ninth century illuminated psalter which is a key masterpiece of Carolingian art; it is probably the most valuable manuscript in the Netherlands. It is famous for its 166 lively pen illustrations, with one accompanying each psalm and the other texts in the manuscript...

; the pen drawing from about 830 goes back to a late antique original. The Luttrell Psalter
Luttrell Psalter
The Luttrell Psalter is an illuminated manuscript written and illustrated circa 1320 – 1340 by anonymous scribes and artists...

, dating to around 1340, describes a grindstone which was rotated by two cranks, one at each end of its axle. Around 1480, the early medieval rotary grindstone was improved with a treadle
Treadle
A treadle [from OE tredan = to tread] is a part of a machine which is operated by the foot to produce reciprocating or rotary motion in a machine such as a weaving loom or grinder...

 and crank mechanism.