This page will feature a growing number of animated illustrations
showing the structure and workings of Chinnor windmill.
Clicking on the animations should show them at their full size
(These are extracts from the set of scale drawings which can now be provided for model makers etc)
The mill 'buck' is mounted on a 'trestle' on which it is turned, to keep the sails pointing into the wind.
The sails have 'patent' shutters which automatically open to spill hazardous gusts of wind, and which were also used to control the speed of the mill.
They are controlled by a counterweight system that hangs off the rear of the mill.
The sails are turned by the wind and a series of gears take this power off to a rotary sieve on the upper floor, and down to 2 pairs of under-driven stones on the lower floor.
Tentering is the setting of the gap between a pair of stones to get the right degree of grinding of the grains, and hence good flour quality.
Chinnor windmill has 2 pairs of stones, the ‘mill stone grit’ stones on the starboard side are manually adjusted, and the ‘French burr’ stones on the port side have manual setting with a supplementary governor system to automatically maintain a steady grind speed despite changing windspeeds.
Manual is ok, but if the windspeed
increases, you’ll have more power so you could
grind harder and increase your production (but if the wind then drops you’ll need
to open up the gap again).
So in combination with the
miller’s wingnut adjustment, a speed sensitive governor is used to automatically
make additional gap adjustments to keep the speed of the stones consistent,
despite changing winds; it decreases the gap (and so grinds harder) if the wind
speed increases and opens up the gap again (reducing the grinding load) when the
wind dies back.
As for the manual version, the top ‘runner’ stone is supported on its drive shaft supported on the ‘bridge tree’ and ‘brayer’ with a wrought iron bracket positioned by a wingnut adjustment to give the miller his base setting.
However unlike the manual system which adjusts the wingnut against the fixed ‘hurst’ frame, this wingnut adjusts against a shifting speed governor control rod, and it’s the additional movements of this control rod which add in automatic adjustments of the gap, dependant on mill speed:
If the mill is going too fast because of strong wings, the governor weights will fly out, which causes stone gap to close, making them grind the grain harder, making the mill stones work harder and so slowing the mill down.