Windmills are charming decorative features for any garden. They conjure up images of Dutch children in clogs and the heroic quest of Don Quixote. Once a common feature of the countryside, the traditional windmill all but disappeared with the advent of rural electrification. Today, windmills are making a comeback as the graceful turbines that, like their older cousins, have begun to dot the countryside to provide energy once again. Build a windmill and declare your support for alternative energy.
Pick a style of windmill. Fixed windmills, like the ones seen around the Mediterranean are built in areas where the wind blows almost always from one direction. The windmills we call "Dutch" and UK farm windmills have blades, or "sails" mounted in assemblies that can rotate so the blades can always catch the wind. If your windmill is decorative only, you may want to avoid the extra equipment it takes to carry the extra load of a rotating head assembly and use the design of your choice with a fixed head assembly.
Choose a location for your windmill where it will have space and exposure to the wind. You'll need vertical space, unobstructed by wires and trees. A "Dutch" windmill that rotates will need space all around to accommodate the sails. A traditional fixed windmill will need space for the arms in one position only.
Build your windmill base of wood, metal, brick or stone. The head assembly is the critical part because the sails and fantail ride on it. Farm windmills have steel assemblies that are fairly compact. Older designs use a wooden axle, fantail and wheels with iron or steel gears. Depending on the type of mill you're building, these components must be installed so that the blades sit on an axle that turns a gear that meets another gear at a right angle. This gear will turn the axle that runs the mill or pump at the bottom of the mill. The little fantail on some windmills functions as a governor, controlling the turns of the cap of the mill. The wheel that the fantail runs on should be attached to the inside of the mill itself while the head assembly rotates with the cap. Steel and reconditioned head assemblies are available online.
Build your mill to meet your needs. Use solid steel blades for farm windmills but larger "sails" of canvas draped over wooden blades for larger fixed and traditional mills. The traditional lattice sails are familiar as UK or Dutch windmills and the fixed Spanish windmills of Don Quixote. Tilt sails slightly to accept the wind needed to move the head assembly. Build only a lattice or arm for mills that will be decorative. Get some engineering help to design and install a pump for aerating a pond or pumping water.
Remember that you are building your mill to support not only the weight of the sails but the "load" of the sails plus the wind. Your mill must be strong enough to withstand the forces of the strongest average winds in your area.
Windmill building is a science as well as an art. Unless you're an engineer or machinist, buy some prepared plans and find a reliable source for precision parts.