millwheel

Millwheel is the term for the wheel at the heart of traditional mills, used to convert energy from water or wind into rotary motion to power milling or other mechanical processes. The design and arrangement vary by source of power and era.

Water-powered millwheels come in several types: overshot, where water fills upper buckets and gravity drives rotation; undershot, where flow beneath the wheel moves it; and breastshot, a compromise using water at mid-height. Each type has trade-offs in efficiency, construction, and suitability to river conditions. Wind-powered millwheels, or windmills, use a rotating wheel with blades or sails aligned to capture wind; the geometry and number of sails affect performance and drag.

Historically, millwheels date to antiquity and became central to agrarian economies in medieval Europe and Asia, enabling grain milling, sawing, and metalworking. Water wheels improved with better bearings, gear trains, and use of high-head sites, while windmills expanded in regions with suitable winds. The introduction of steel gears and steam power reduced dependence on water or wind during the Industrial Revolution, but mills continued to operate in rural areas and as heritage sites.

Today, millwheels survive mainly as historical artifacts or in functioning heritage mills. Modern hydraulic and turbine installations may replace traditional wheels for efficiency, but some communities preserve older mills for education, tourism, and crafts. In some cases, small-scale micro-hydropower reuse traditional wheel concepts with modern bearings and materials.