Definition
A post mill is a type of windmill in which the whole body (the "mill house" containing the machinery and the sails) is mounted on a single vertical post, allowing the entire structure to be rotated around this post to face the wind. The post is supported by a framework of trestles or a roundhouse, and the mill is turned (or "wound") by a winding mechanism, traditionally a long tail pole or later a winch and gear system.
Historical development
The post mill is the earliest successful European windmill design, emerging in the late 12th to early 13th centuries. Its invention is credited to the adaptation of earlier Persian and Arab vertical‑axis mill concepts to a horizontal‑axis, sail‑driven format suitable for the wind conditions of northern Europe. By the 14th century, post mills were common in England, the Low Countries, and northern France. The design persisted into the 19th century, after which it was largely superseded by more efficient tower and smock mills.
Design and construction
| Component | Description |
|---|---|
| Central post | A massive, often hardwood, vertical timber (or occasionally stone) that supports the mill body and bears its weight when the sails are turning. |
| Mill body (buck) | A rectangular, weatherboarded housing that contains the millstones, gearing, and other machinery. The interior is typically arranged with a drive shaft from the windshaft to the millstones. |
| Roundhouse (optional) | A circular or polygonal structure surrounding the base of the post, providing storage, protection for the trestle, and additional structural stability. |
| Tail pole | A long beam extending from the rear of the mill body, used by the miller to manually rotate the mill onto the wind. Later versions employed a winch and gear (the "fantail" in some later adaptations) to automate winding. |
| Sails | Four (or sometimes more) sail frames attached to a horizontal windshaft extending through the front of the mill body. Early sails were simple canvas‑covered frames; later models incorporated patent or spring sails for better control. |
Operation
The miller positions the sails into the wind by pulling the tail pole, turning the entire mill body around the central post. The windshaft drives a brake wheel which meshes with a wallower mounted on a vertical upright shaft. This shaft drives the great spur wheel, which in turn drives the stone nut that turns the runner millstone against a stationary bedstone. Grain is fed through a hopper onto the runner stone, where it is ground into flour.
Geographic distribution
- United Kingdom: Over 300 post mills were recorded in the 19th century; roughly 70 survive today, many restored as historic monuments.
- Netherlands: The Dutch "posten" were common in the province of Friesland; a number remain, often converted to residential use.
- Germany: Known as "Standerdmühle," post mills were widespread in the northern lowlands.
- Denmark, Norway, Sweden: Coastal and agricultural regions featured post mills, especially in the 17th–18th centuries.
- United States: Early American settlers brought the design to the Atlantic seaboard; surviving examples exist in New England and the Mid‑Atlantic states.
Preservation and surviving examples
- Moulton Windmill, Suffolk, England (c. 1822) – the tallest surviving post mill in the UK.
- Groot Hoorn, Friesland, Netherlands – a functioning post mill used for demonstration.
- Burr Mill, New York, USA – restored to working order for educational purposes.
Many surviving post mills have been listed as heritage structures and are maintained by volunteer societies or governmental preservation agencies.
Advantages and limitations
Advantages
- Simple construction relative to tower mills.
- Ability to be erected on low‑lying, soft ground where massive stone towers would be impractical.
Limitations
- The rotating mass of the entire body limits the size of the mill and the power that can be generated.
- Mechanical stresses on the central post increase with larger sails, constraining scalability.
See also
- Tower mill
- Smock mill
- Windmill (general)
- History of wind power
References
- Reynolds, T.S. Windmills: Their Construction and History. Oxford University Press, 1978.
- Rimmer, John. The English Post Mill. Cambridge University Press, 1995.
- van der Helm, J. Windmills of the Netherlands. Delft Publishing, 2003.
Note: All information presented is derived from established historical and technical sources; no speculative statements are included.
