There has been a mill on the site of Acorn Bank Watermill for hundreds of years although the current building dates from the late 18th century. The mill was the manorial mill of the Acorn Bank Estate, also known as Temple Sowerby Manor for a while, and the miller was a tenant. The earliest mention of a mill is in 1323 when the estate passed from the Knights Templar to the Knights Hospitaller and at the time the mill gave an annual income of £4. The machinery suggests that substantial changes were made around 1840 when a French Burr millstone was installed. The original building is constructed of coursed squared rubble with quoins and although primarily a corn mill, the mill has also been used to provide power to the estate gypsum mines. The mill ceased to work in the 1940’s and gradually fell into a state of ruin.
Restoration began in the late 1980’s and the Watermill was little more than a ruin. Many of the walls have had to be dismantled and completely rebuilt yet much of the machinery survived and has been retained. The mill is now partially restored and has been open to the public since 1996. Flour was ground again for the first time in September 2011. The water supply for the mill starts at a weir and sluice on Crowdundle Beck – about a quarter of a mile upstream of the mill. The weir directs water into the millrace and the sluice allows the miller to control the amount of water that flows to the mill. The race has a very shallow fall while Crowdundle Beck drops more rapidly. By the time the millrace reaches the mill, the water in it is about four metres above the river level and high enough to pass over the wheels.
Acorn Bank Watermill is unusual in that it has two sets of mill machinery driven by separate waterwheels. The upper set of machinery (above) is virtually complete with two pairs of millstones for grinding grain and making flour. This set of mill machinery is driven from the uppermost of three waterwheels. The large vertical cogwheel is on the same shaft as the waterwheel. This cogwheel is the pitwheel and it turns the smaller gear, the wallower, on the vertical shaft. The great spur wheel is the large gear above the wallower and this could be made to drive either or both of the millstones via the small ‘stonenuts’ to each side of the great spur.
The lower set of mill machinery (above) is no longer complete but was once almost identical to the upper set. The large cogwheels were probably removed when the waterwheel was adapted to provide power to a local mine. The lower set of mill machinery, like the upper set, has two pairs of millstones and was driven from the middle of three waterwheels.
The drying kiln (above) was used to dry the oats before they were milled. A floor of perforated tiles existed above a fire and the oats were spread over the tiles which were dried from the heat of the fire. Suspended above the kiln fire was a baffle plate which spread the heat more evenly and prevented a hot-spot on the floor above. The perforated tiles of the drying floor were supported on cross beams of stone and slate and later, iron. The earliest tiles were made of roughly fired clay with holes punched through. The oats were spread over the floor to a depth of a few inches and were turned regularly to prevent the lower grain burning and to ensure an even drying. The miller would be able to tell when the grain was dry enough by biting it. Once dry, the grain was swept off the drying floor to be milled.
There were once three waterwheels at Acorn Bank. The top and middle wheels drove corn milling machinery while the bottom drove a saw bench. The middle wheel was adapted to provide power for a nearby gypsum mine. There were two types of wheel in use at the mill. The upper wheel is a pitchback meaning that the water falls onto the top of the wheel at the back and the middle and bottom wheels were overshot meaning that the water falls onto the wheel at the top. In both cases, the water fills buckets and its weight turns the wheel. The bottom wheel was situated below the mill building.
Acorn Bank Mill is Grade II Listed.