Illustrations

This page will feature a growing number of animated images and 'walk-through' animations

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)

Design

The mill 'buck' is mounted on a 'trestle' on which it is turned, to keep the sails pointing into the wind.

Originally the miller would have turned the mill by hand but Chinnor had an automatic fan tail fitted at the rear to do this for him- any side winds would turn the fantail which was geared to slowly drive large iron wheels, until the mill was once again pointing into the wind.

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.

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.

Operation

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 tentering:

Automatic tentering:

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:

SO..

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.

When the wind drops, so do the governor weights, and so the gap is opened back up again. 

The windmill is being put into 3d CAD (Solidworks) by CraftyTech

The first few pictures show the mill as it appears currently, with its 6 footed trestle exposed:

(This line drawing could be used as a colouring sheet)

However we intend to reinstate the Flemish-bond 'roundhouse' (actually 12-sided), when funds become available, in order to protect the mill's unique trestle construction and provide dry storage for our winnower:

The timber framing of the mill and its machinery are included in the CAD model.....

.

...to produce accurate illustrations to fully document how the mill was constructed, and how it operates,

for example accurately recording the decreasing twist along each sail as you move to the tip (and showing the resultant complexity of the angled and offset mortices required for the sail bars!):

Animations and walk-throughs:

Fly-by and into the roundhouse:

Walk-by and up the ladder:

Inside the buck (lower floor)

The mill mechanism has been surveyed and fully modelled by Crafty Tech 

(detailed stills can be found on the construction page)