For farmers, millers, engineers, and artisans who live near a river or stream, a monjolo or kara-usu—a water powered hammer—can slowly grind grains into flours or soft stones into powders without repetitive human effort. Watch as Primitive Technology builds a monjolo, as well as a few other useful tools along the way. From his site:
The trough filled with water, outweighed the hammer head and tilted the hammer up into the air. The water then emptied out of the trough (now slanting downwards) and the hammer then slammed down onto an anvil stone returning to its original position. The cycle then repeated at the approximate rate of one strike every 10 seconds. The hammer crushes small soft types of stone like sandstone or ochre. I carved a bowl into the anvil stone so that it would collect the powder. I then crushed old pottery (useful as grog for new pots) and charcoal. Practically speaking, this hammer worked ok as a proof of concept but I might adjust it or make a new one with a larger trough and bigger hammer for heavy duty work.
Here’s another example of a kara-usu, filmed at the Onta Pottery Village in an area of Japan known for its generations of Onta ware pottery. According to the vid notes, the watermill crushes the clay into powder over 20-30 days.The 1,000 year old windmills of Nashtifan, The physics & engineering of windmills in The Netherlands, and plastic bottle water wheel power generator experiment.