Brief description

A windmill is a structure that converts the kinetic energy of the wind into rotational energy using sails or blades. This energy is used to grind grain, pump water, or drive other machinery.

Use / Function

• Milling: Grinding grain into flour (gristmill).
• Pumping: Draining wetlands or pumping water for irrigation (windpump).
• Sawing: Cutting timber in sawmills.
• Industrial: Crushing seeds for oil, processing Spices, or fulling cloth.
• Scale: Industrial / Local community.

Operating principle

1. Capture: Wind pushes against the angled sails or blades, creating lift and drag that rotates the windshaft.
2. Transmission: The windshaft (horizontal or slightly inclined) connects to a large brake wheel.
3. Gearing: The brake wheel drives a wallower (lantern gear) on a vertical main shaft, converting the motion from horizontal to vertical.
4. Application: The vertical shaft drives the millstones (via a spur wheel and stone nuts) or a scoop wheel/Archimedes’ screw for pumping.

How to create it

1. Foundation: Build a stable base (brick, stone, or timber trestle) to support the weight and resist wind forces.
2. Structure: Construct the tower or body. For a “Post Mill,” the whole body rotates on a central post. For a “Tower Mill,” only the cap rotates.
3. Sails: Construct the framework for the sails (usually 4) from light, strong wood. Cover with canvas (fabric) sails that can be adjusted based on wind speed.
4. Mechanism: Install the windshaft, brake wheel, vertical shaft, and gearing. Use hard wood (like oak) or iron.
5. Millstones: Install the bedstone (fixed) and runner stone (rotating).
6. Orientation: Add a tail pole or fantail to manually or automatically turn the sails into the wind.

Materials needed

• Structure: Strong timber (oak) or masonry (brick/stone) for the tower.
• Sails: Light timber lattice and strong fabric (canvas) or wooden shutters.
• Gears: Hardwood (apple, hornbeam) or cast iron for durability.
• Millstones: Hard, abrasive stone (burrstone, granite).
• Rope: For controlling the sails and brake.

Variants and improvements

• Post Mill: The earliest type; the whole building turns to face the wind. Limited size.
• Tower/Smock Mill: Only the top cap rotates. Allows for a larger, more stable building.
• Fantail: A small fan at the back that automatically turns the cap into the wind.
• Spring/Patent Sails: Shutters that open/close automatically to regulate speed, replacing manual canvas handling.

Limits and risks

• Intermittency: Does not work without wind; useless in calm weather.
• Storms: High winds can destroy the sails or burn down the mill (friction fire) if the brake fails.
• Maintenance: Sails wear out quickly; gears need constant greasing (animal fat).
• Safety: The rotating sails are heavy and fast; being struck is fatal. Brake failure can lead to runaway speed.