Wind Milling Principles


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The Principle of a Post Mill.

 

The entire ‘body’, which contains the main floors, millstones and machinery, is built around a central timber post allowing it to rotate and for the ‘sweeps’ to face into the wind. The sweeps are mounted on the end of a cast iron axle called the ‘windshaft’. The windshaft also carries 2 large cogged wheels called the ‘brakewheel’ and the ‘tailwheel’. The wind pressure against the sweeps causes them to revolve with the windshaft, brakewheel and tailwheel. In an overdriven arrangement the brake and tail wheels each drive a small cogged wheel called a ‘stone nut’. Each stone nut is mounted on a small vertical shaft (called a ‘quant’), which drives the millstone from above.  The upper millstone (called the ‘runner stone’) revolves and the lower millstone is permanently stationary (called the ‘bed stone’). The cogs in the brakewheel also drive the gearing for the ‘sack hoist’ and the ‘flour dresser’.

The Milling Process.

Sacks of grain are raised to the top of the mill using the ‘sack hoist’ which consists of a wooden roller in the peak of the roof and a long chain which passes down through trap doors in each floor. The sack hoist is driven by wind power. The grain is poured into large bins and then descends down spouts into the wooden ‘furniture’ surrounding the millstones. The various components within the furniture direct a constant trickle of grain into the hole in the centre of the runner stone. The action of the runner stone rotating over the bed stone reduces the grain into meal. It is important to realise that the millstones never actually touch – there is a very fine gap between them. The ground ‘meal’ emerges from the edge of the millstones and is automatically swept down a hole into another spout. This spout transports the meal into ‘meal bins’ providing an opportunity to cool down before it is put into sacks. The gap between the millstones can be adjusted manually by the miller using the ‘tentering screw’. He would feel the meal between his thumb and forefinger as it emerges from the spout and from experience would know how to adjust the tentering screw.

Dressing the Flour.

The meal becomes flour once it has passed through the ‘flour dresser.’ The flour dresser consists of an inclined wooden framed cylinder lined with different grades of wire gauze. Inside the cylinder are a set of long horse hair brushes mounted on a central shaft which rotates using wind power. Meal is fed into the top end of the cylinder and the different grades of flour pass through the various grades of wire gauze. It is collected from below in three different sacks –  ‘fine’ flour, ‘middlings’ (coarse flour) and ‘bran’.