The Knife-grinder by Goya shows a man using a portable grindstone.
Large waterwheel powered grindstone. The user would lie on the plank above the grindstone while grinding metal items, giving rise to the phrase nose to the grindstone.
A grindstone is a round sharpening stone used for grinding or sharpening ferroustools. 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 Psalter. This pen drawing from about 830 goes back to a late antique original. The Luttrell Psalter, dating to around 1340, describes a grindstone rotated by two cranks, one at each end of its axle. Around 1480, the early medieval rotary grindstone was improved with a treadle and crank mechanism.