How the mill works

The mill building sits astride the mill leat, and houses two independent mills sharing the same stream. There are two water-wheels, which would previously have driven two pairs of milling stones housed in each mill. With a total of four pairs of stones, Otterton Mill was for much of its life the largest watermill in Devon. Today, one of the waterwheels is still in working order and allows us to mill the stoneground wholemeal flour for which we are famous. The second waterwheel is sadly no longer in use and needs complete rebuilding.

Sluices: The mill stream which drives the waterwheel probably predates the middle ages, and flows off the River Otter. It has three sets of sluice gates, which are raised and lowered to control the flow of water to the wheel. The head sluice controls the water intake from the River Otter into the mill stream. The middle sluice is a by-pass to divert excess water back to the river and to control flooding in the village. The third sluice, sited within the mill building and just ahead of the waterwheels, allows for final adjustments. This sluice has three gates: one gate for each waterwheel and a third to release the water when both the waterwheel sluice gates are closed. All the sluices and the mill stream have to be regularly checked, repaired and cleared of weeds and sediment to allow the free flow of water.

Waterwheels: The two waterwheels are each 3m in diameter, and were made in Exeter in 1827 by "Bodeley Brothers". One is now derelict and has the original 500mm diameter wooden shaft and wooden paddles. The wheel in use today is on a 150mm steel shaft and is fitted with steel paddles. Both are modified "Poncelet" type wheels. They work to maximum efficiency by having the water directed into the wheel around 500mm above its lowest point, through curved blades that come closer together to increase the water speed and carefully direct the flow onto the paddles. The wheel fits very closely into the brick walls, with only around 12mm clearance under the paddles to the curved brickwork beneath it.

Mill Stones: The mill stones at Otterton have different origins. We have two magnificent pairs of French burr stones from the Jouarre quarry in the Paris basin, a famous source of millstones in the 19^th century. These stones are inscribed with rhyming dedications from the proud miller who purchased them, John Uglow. One reads: "This time worked the first time, tis true, May 1^st, 1862". The stones are now on display on the first floor of our gallery. The stones we use for milling today are called composition stones, so-called because they were made according to the individual recipe of the manufacturer, and consist of fine chippings held together with a cement mortar.

Each millstone has a pattern of grooves cut into its grinding surface to help the grain travel from the centre outwards to the sides, being ground up on the way. The pattern on our stones is a fairly unusual curved design. The top 'rotating stone' is turned by another vertical shaft from below, through the centre of the 'fixed stone' which sits on the first floor of the mill building," the milling floor". The rotating stone and shaft are driven by the vertical shaft via a great spur wheel and pinion, with a ratio of about 4 to1. This pinion wheel can be disengaged by raising it above the spur wheel to stop the stone rotating. A horizontal lay-shaft is driven via another crown wheel and pinion. This is used for auxiliary work such as hoisting grain, flour conveyors and elevators or any other machinery as needed by the miller. Both the milling stone and the lay-shaft rotate about ten times for each rotation of the waterwheel. The yield today is easily 150kg of flour per hour. The great spur wheel and the lay shaft crown wheel have wooden teeth turning cast iron pinions.

Milling: The miller's job is one that requires great skill, and a thorough understanding and respect for the milling machinery and the elemental forces that are powering it. The miller needs to make three main adjustments when grinding flour. Each one affects the other. These are:

• The flow of water, as controlled by the sluice gates. This controls the rotation rate of the waterwheel. Optimum is about 12 revolutions/minute.
• The clearance of the rotating mill stone over the fixed stone, set by raising or lowering the bottom shaft bearing with the bridge tree, using a screw. The closer the stones, the finer the flour.
• The rate of feeding the grain into the mill stones, as set by raising or lowering the shaker shoe under the hopper. The slower the feed the finer the flour. If the grain stops flowing, the mill stones will grind against each other, get overheated, worn and probably damaged.

Dressing the Stones: Every 100 to 200 tonnes of grain, the mill stones have to be dressed. In use, the faces of the stones become polished and the grooves for pulling-in the grain become too shallow. Dressing involves roughening the surfaces of the mill stones and re-cutting the grooves. Dressing the stones is a highly skilled job as the working surfaces of the stones have to remain perfectly flat. To do this, the hopper and the circular box around the stones (which keeps the flour from spreading and directs it to the bagging area on the ground floor below) are removed.

The top stone is lifted and turned over. Once both stones are dressed, the lower stone is re-levelled if necessary. The bearing for the shaft in the centre of this stone is cleaned, re-packed and re-lubricated. All the other shafts are checked for alignment and all bearings are lubricated. The top stone is now lifted, turned over and carefully replaced and the box and hopper are put back in position over the stones. After testing, milling can start again.