Grindstone Wikipedia
A grindstone is a round sharpening stone used for grinding or sharpening ferrous tools. Grindstones are usually made from sandstone. Grindstone machines usually have pedals for speeding up and slowing down the stone to control the sharpening process. The earliest known representation of a rotary grindstone, operated by a crank handle, is found in the Carolingian manuscript known as the Utrecht