Windmills in History

The machinery in an old windmill is mostly made of wood, this is because iron was scarce and wood was plentiful in those times. Some of the nails holding the pieces of wood together were even made of wood - called treenails. The main shaft was made of oak. On the front were mounted usually four sets of sails; these had a timber framework on which the miller stretched canvas sails. He could change the amount of canvas exposed to the wind to regulate the working of the windmill.

Right behind the sails was the front bearing which carried nearly all the weight of the shaft and sails. This was made of stone and only went about one third the way around the shaft, it was lubricated using two-year-old uncooked pig-fat. Pieces of this were kept hanging from the roof near the neck bearing.
At the back end of the shaft was the tail bearing, which was the thrust bearing which took all the pressure of the wind against the sails.

On the main shaft between the two bearings was mounted the brake wheel. This had a brake around its outside rim, which the miller used to stop the mill. It also had teeth set into the side of the rim to take the power from the wind shaft to the rest of the machinery. The cogwheel, which connected with the teeth on the brake wheel, was called the wallower and through a vertical shaft, it drove the stones around. There were different numbers of teeth on these wheels so that the slow speed of rotation of the windmill sails could be matched to the faster speed of the grinding stones. Apple wood was often used for the teeth, as it was able to absorb the shock loads without breaking.

The grain is fed down between the grinding stones, the bottom one is fixed and the upper one rotates and has a hole in the middle through which the grain is fed. The clearance between the two stones is very small and can be adjusted by the miller to grind the grain correctly into meal.

Turning the Mill to face the wind

The miller used an internal winch or cog mechanism to turn the cap of the mill to face the wind on the tower/smock mill. The post mill was turned using its tail pole. Later on, around 1700, wooden roller bearings were introduced into the caps of the tower and smock mills and the sides of the mills were tapered. This allowed the cap to be relatively small while allowing more room lower down for the grinding machinery. It also allowed tail poles to be used to turn the caps on the tower mills.

The cone shaped tower/smock mill was a stronger shape than the older mills with vertical walls and could be built higher allowing longer and bigger sails and more powerful machinery. By the mid 1700's quite large windmills were being built with tower heights of up to 90ft and sail diameters of 75 feet. This is not far from the size of modern wind turbines being built over 200 years later! It was at this time that the traditional windmill reached the very pinnacle of its development. The only real improvement after this was the introduction of cast iron main shafts in the early 1800's.

Ship of the Land

A windmill is like a ship of the land; it stands there between earth and sky with its arms outstretched capturing the wind. Standing in an old mill while it is working, the mill seems to be alive. It creaks and groans and demands constant attention from the miller. In Schedam in Rotterdam five of the original eighteen windmills built around 1780 still survive and still work at their original task. Few other machines made by man could have such a long working life. Windmills were providing mankind with much needed power over 1000 years ago and of all the technologies available today it can be predicted that they will be doing the same in 1000 years time.

Modern Wind Turbines

The modern wind turbine uses exactly the same components as the post mill.

• The steel tower takes the place of the wooden post.
• The nacelle containing all the machinery takes the place of the body of the post mill.
• The fibreglass blades take the place of the wood and canvas sails.
• The gearbox takes the place of the wooden gears.
• The electrical generator absorbs the power instead of the mill stones.
• An electric motor turns the top to face the wind instead of a tail pole.
• An electronic computer regulates the mill and applies the brakes instead of the miller.

An eight hundred and fifty year old invention still being used today! It is interesting to note the evolution of wind turbines from the noisy, whirring youngsters of just fifteen years ago to the slowly turning stately giants of today. They are becoming like their grandparents of two hundred years ago - history is repeating itself.

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