Educational Projects
How Millstones Grind
Robert P. Rich and Steven A. Walton
Learning Objectives
  • Students will create a model that demonstrates how stones grind.
  • Students will compare millstone patterns to identify how the grain is turned into flour as it runs from the central hopper to the perimeter.
Millstones at Daniel's Mill In order for a millstone to cut the grain into flour - for that is exactly how grain is ground - the millstone faces need to have grooves cut into them. The pattern of these grooves varied from stone to stone and from region to region, and stone dressers developed both elaborate and subtle variations for different grains, different grinds (much like the range of grinds of coffee available today), and different grain conditions. The patterns on the stones working together act like a pair of scissors to cut the grain as the stones rotate.
When we speak of a grindstone, we can either mean each of the pair or the two together, for you must have a pair to do any useful grinding. The bottom stone is called the bedstone and it remains stationary - in fact, it is set into a bed of concrete or mortar to make it literally rock stable. The top, rotating stone is called the runner stone, and it has a hole in the middle through which the grain is fed. Both stones have a pattern of grooves cut into their working faces (top face for the bedstone and bottom face for the runner stone) that act as feed channels for the flow of the grain to the outside edge. As the two stones rotate against one another - never touching! - the grain is repeatedly scissored between the grooves, whose gap varies from well less than 1/8" near the center down to thousandths of an inch at the perimeter. Individual grains are cut again and again on their journey from the center out to the edge. A stone dresser would come to the mill once a year and re-face the stones to keep the grooves crisp and the stones milling smoothly through the year.
Versitile Millstone For more information on the patterns in millstones, see Jon A. Sass, The Versatile Millstone: Workhorse of Many Industries (SPOOM, 199), available directly from SPOOM.
For each model of a millstone pattern, you will need the following:
  • 1 sheet 8.5x11 piece of cardstock (back of a writing pad, corrugated cardboard, or tagboard)
  • 1 or more templates (below) for the "bedstone"
  • 1 overhead transparency sheet for the "runner stone"
  • 1 brass paper fastener clasp
    brass paper fastener
  1. Poke a small hole in the very center of the piece of cardboard.
  2. Print a millstone template from these options (click each image below to get a new window with full-sized image for printing) :
    millstone eighths millstone quarters millstone quarter millstone star millstone sickle
    OR, have the students draw an approximately 7" circle on a sheet of paper and create their own pattern based loosely on the templates above.
  3. Photocopy the millstone pattern onto an overhead transparency and cut out the circular millstone pattern.
  4. Assemble as shown in the diagram to the right (click to enlarge), using the brass paper clasp.
  5. Once assembled, rotate the transparency to see how the patterns intermesh.
  1. What is the path of the grain through the stones as they grind? That is, which way does it seem to "flow"?
  2. Which way does the grain seem to flow when you rotate the runner stone?
  3. Does the grain seem to flow the other way when you rotate the runner stone the other way? What does this suggest about running a millstone in either direction?
  4. Flip the transparency (runner stone over) and see how having the patterns identical or reversed affects the flow.
  5. Use different patterns for the bedstone and runnerstone - how does this affect the flow?
  6. Make up numerous patterns and combinations and design your own and have the class discuss which seem to have the fastest "flow".