A windmill is a structure in which wind power is converted by sails into a rotating movement, transmitted through shafts and gearing to a machine. That machine grinds grain, saws timber, presses oil or lifts water. In the Netherlands — the country with Europe’s densest concentration of mills — roughly 1,200 working mills survive, and virtually all of them are protected as monuments.
The main types
- Post mill — the oldest timber type: the entire mill body turns on a heavy vertical post. Only a few survive
- Hollow post mill (wipmolen) — developed from the post mill, mainly as a drainage mill. Only the upper body turns; the base stands still
- Ground sailer (grondzeiler) — a mill without a stage, whose sails reach almost to the ground, so the miller works the sails standing on the ground
- Mound mill (beltmolen) — the tower stands in a raised mound so the sails clear the ground while the miller still works at ground level
- Smock or tower mill with a stage (stellingmolen) — a tall mill in a built-up area, with a gallery at mid-height from which the miller works the sails
Application
Structurally a mill is unusual because it has to be able to rotate, has to be turned into the wind, and takes large and variable loads at the same time.
- Winding. The cap or upper body is turned into the wind with a winding wheel or winch. If it cannot be turned, work stops whenever the wind is in the wrong quarter
- The brake. The brake acts on the brake wheel. A mill left in the wind without its brake applied can run away
- Free wind access. New building or tall trees near a mill take away its wind. Local authorities therefore often protect a zone around a mill in the planning framework; take this into account for building plans nearby
- Maintenance. Thatch or slate covering, the sail cross, wooden gearing and the cap all need continuous care. Work on a mill belongs to a specialist millwright; ordinary carpentry is not enough
Related terms
- Listed building
- Thatched roof
- Roof structure
- Carpenter
- Planning permission
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