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How a Smock Mill Works

A smock mil is constructed of wood and often sits on a brick base, a sketch of a typical smock mill is above. It differs from a post mill in that the body does not rotate, like a tower mill its the cap that rotates to face the wind.

The image on the right is of a typical small smock windmill, and the photo below is of the same windmill.

Another labelled up drawing of West Blenchington smock mill can be seen by clicking here.

Smock mills can be larger, the tallest smock mill in Britain is the Union Mill at Cranbook in Kent, which is larger than many tower mills. It measures 70 feet, and is 7 storeys including a brick base 3 storeys high.

Illustration by Clem Rutler 2007   

The rotatable cap holds just the roof, the sails, the windshaft and the brake wheel, plus the fantail and mechanism to rotate the cap into the wind.

When the wind veers it strikes the sides of the vanes, turns them and by a connection the track wheels also, turns the cap until the sails are again square into the wind.

The smock mill structure is a tapered tower clad in weatherboard and is usually octagonal in shape but can vary from six, to twelve sides. Most smock mills are built on a brick base and this was done to protect the base of the mill from rotting, which is one of the major disadvantages of any timber clad construction. It also lifts the windmill above many local obstacles.

The main structure of a smock mill is its 'cant' or corner posts which extend to the full height and converge as they go towards the top. The bottom of these 'cant post' were secured to a wooden sill which was bedded onto the top of the brick base. The joint between post and sill was always a problem and because the post leaned inwards the weight of the mill was bearing down and out at the sill. If there was any inherent weakness in the post/sill joint it could cause the post to slip away and the weight of the structure would topple the mill.

Horizontal ledges were fixed at intervals between the posts and spaced evenly up the structure. Extra vertical and diagonal struts were fixed between posts and ledges to form a rigid structure. The outside was usually clad with horizontal weatherboarding although there are examples of vertical clad smock mills.

   Killicks Mill, Meopham, Kent

Picture by Clem Rutler 2007



Terminology that you may come across includes:-

Sweep, this is the sail.

Stock, is the supporting arms onto which the sales are fitted, when you see a windmill with just a number of large poles instead of sails its the stocks that you can see.

Iron Cross, the fitting that the stocks connect into.

Windshaft the shaft that the iron cross is connected to, and sticks out of the cap.

Brakewheel, connected to the windshaft this is clamped by blocks or a brake to stop the mill or slow it down. It is a large cog wheel that meshes with the wallover.

Wallover, is a cog wheel that is meshing with the brakewheel, that transfers the drive from the windshaft coming in from the side to the drive shaft that runs vertically. In effect its a very large cog wheel at the top of the drive shaft.

Drive shaft or main drive shaft, this is the vertical shaft that rotates and off which all other drives come to run any part of the equipment.

Fantail, sitting on the cap, this detects changes in wind direction and via a drive arrangement is able to turn the cap so that the windmill always faces into the wind.

Curb, truck wheels and rollers, the mechanism that allows the cap to rotate on top of the main body.

Centrifugal governor, as a weight spins around it's thrown outwards, and this is relative to the speed. This action is connected to a mechanism that can make adjustments to the sweeps so that the windmill runs  constantly at the same speed as the wind goes up and down, the whole system has a lot of weight and therefore inertia so tends to average out variations in the wind.

Auxiliary drive, other drives coming off that can drive other equipment.

Stone assembly and stones, used for grinding.

Stone nut, Pinion which engages with the spur wheel and drives the millstones in a corn mill.

Great spur wheel, a large gearwheel which, together with a smaller gear called a pinion, connects two parallel shafts and, in a corn mill, drives the stone nuts.

Bridge tree,  an adjustable, horizontal beam, supporting the vertical stone spindle, which allows the gap between the grinding stones to be varied.

Tentering screw and brayer adjusts the gap between the mill stones. This is the mechanism by which the miller may adjust the gap between his millstones while they are running. As he turns the giant wing-nut he raises or lowers the end of the cross beam, the centre of which in turn supports one end of the bridge beam that carries the shaft with the runner-stone on top. Having set the stones correctly, at the start of a day's work, the only adjustment he needs is to compensate for the expansion of the stones as they warm up during use. This tweaking may well require less than one full revolution of the tentering screw throughout the day.

A Frame, is the supporting frame that folds up the bottom of the main drive shaft, effectively transferring the weight out to supports.

Sack hoist, a mechanical hoist that is driven from an arrangement from the wallower that allows sacks to be lifted vertically right up through the mill. Often you will see a continuous chain arrangement where the chain goes through a hole in or between two doors that open up as sacks come up and shut after so that no one can fall down through the hole.


We have a larger listing of terms used in windmills .

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