Thepost mill is the earliest type of Europeanwindmill. Its defining feature is that the whole body of the mill that houses the machinery is mounted on a single central vertical post. The vertical post is supported by four quarter bars. These are struts that steady the central post.
The body of the windmill can be turned around the central post to bring the sails into the wind. All post mills have an arm projecting from them on the side opposite the sails and reaching down to near ground level. With some, as atSaxtead Green, the arm carries afantail to turn the mill automatically. With the others the arm serves to rotate the mill into the wind by hand.
The earliest post mills in England are thought to have been built in the 12th century.The earliest working post mill in England still used today is to be found atOutwood, Surrey. It was built in 1665. The earliest remaining example of a non-operational mill can be found inGreat Gransden inCambridgeshire, built in 1612.[1] Their design and usage peaked in the 18th and 19th centuries and then declined after the introduction of high-speed steam-driven milling machinery.[2] Many still exist today, primarily inNorthern Europe andGreat Britain. The termpeg mill orpeg and post mill (in which the "post" was the tailpole used to turn the mill into the wind) was used in north-west England, andstob mill in north-east England, to describe mills of this type.
Post mills dominated the scene in Europe until the 19th century whentower mills began to replace them.[3] The advantage of the tower mill over the earlier post mill is that it is not necessary to turn the whole mill ("body", "buck") with all its machinery into the wind; this allows more space for the machinery as well as for storage.
There are many variations amongst post mills.
The earliest post mills were quite small, and this led to problems with stability as they were liable to blow down in strong winds. A solution was found by burying the bottom of thetrestle in a mound of earth.[4] The last sunk post mills in England were atWarton,Lancashire,[5] andEssington,Staffordshire.
As mills were made bigger, it was found that the trestle did not need to be buried. Thus the open trestle post mills were built. The oldest surviving is atGreat Gransden, Cambridgeshire. Others exist in the UK atBourn, Cambridgeshire;Great Chishill, Cambridgeshire;Nutley, Sussex andChillenden, Kent. Open trestle post mills are also found in France, Belgium, the Netherlands, Germany and inNew England, USA.
The space around the trestle could be used for storage, but was open to the weather. Mill owners started to buildroundhouses around the trestles, and later mills were built with a roundhouse from new. This had the dual advantage of creating a covered storage area and protecting the trestle from bad weather. InSuffolk,millwrights would build post mills mounted on tall, two or three storey roundhouses, as atSaxtead Green.
In the Midlands and North West of England, the top of the roundhouse had a curb, and rollers affixed to the mill body enabled the roundhouse to bear some of the weight of the mill. Examples of Midlands post mills extant include Danzey Green mill, (preserved atAvoncroft Museum of Historic Buildings) and the mill atWrawby, Lincolnshire.
In eastern Europe, instead of a roundhouse an "apron" was fitted to the bottom of the body of the mill, enclosing the trestle and thereby affording protection from the weather.
Some post mills are hollow post mills. In these mills the main post is bored to take a driveshaft, similar to an Upright Shaft in asmock ortower mill. This enables the mill to drive machinery in the base or roundhouse. Hollow post mills were not common in the United Kingdom. In the Netherlands, they are calledWipmolen and were mostly used for drainage. In France, theMoulin Cavier was a type of hollow post mill used for corn milling.
A few mills looked like post mills, but were not post mills. These composite mills often had a post mill body mounted on a short tower resembling a roundhouse, as atBanham[6] andThornham[7] in Norfolk. Composite mills lack the central post on which the body of the post mill is mounted and turns upon to enable the mill to face the wind.
In theNetherlands andGermany, a variety of mill called the paltrok (Low German spellingPaltrock, from High GermanPfalzrock (palisade skirt); the shape of the millhouse resembles that kind of garment) was built. Though similar in name and appearance, Dutch and German paltrok mills differ in historical and technical regard.
The Dutchpaltrok mill was invented around 1600 and specifically designed for sawing wood. Several hundred[8] have existed of this type of windmill; however, only five paltrok mills remain in theNetherlands, atZaanse Schans,Haarlem,Zaandam,Amsterdam and at theNetherlands Open Air Museum,Arnhem. Dutch paltrok mills are, like post windmills, supported on a central wooden post around which the entire millhouse rotates. The central post, however, is short and, to provide stability, a rim bearing is added on a brick base, on which the millhouse rotates with numerous rollers. Side extensions protect the sawing floor and workmen from the weather.[9]
Germanpaltrok mills were commonly converted from post mills where the post and trestle were replaced by a wooden or iron rim bearing, set into the ground or on a brick base. The millhouse was enlarged and supported on this rim by numerous rollers or small wheels. These mills are technically composite mills although the tower is very short and of large diameter. This type of mill provided more internal space than a post mill and was cheaper than the alternative of erecting asmock mill.[10]
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