Most of the machinery now to be seen at the mill is Victorian. For example, the "hurst frame" (the heavy wooden framework supporting the gears) was built in the mid-nineteenth century. However, there is evidence of earlier machinery including a wooden water- wheel and gears. The mill is particularly interesting in having a horizontal "lay-shaft" resulting in the three pairs of stones being in a straight line; they are normally arranged around a central circular gear. This is unique in the county and rare throughout Britain - found only in the more technically advanced mills.
Grain would arrive at the mill by horse and cart in sacks from the surrounding farms and the Estate. In front of the mill you can see where the horses drank from the river. In dry summer harvest weather, the cart stood in the water to allow the dry wooden wheels to tighten by swelling as they got wet.
Notice the arrangement of the front door which opens on two levels. As the miller unloaded sacks from the top of the cart straight into the first floor of the mill and the cart became emptier, the lower sacks were unloaded into the ground floor. The sacks of grain had to be taken up to the top floor. This was done by the "sack-hoist". Its chain passed through each floor and could be operated from any level. The sack hoist's chain, mechanism and two operating ropes are still in use and can be seen in the mill today.
Once at the top, the grain was emptied into either a "hopper" or a "bin". The bins (which have not been rebuilt) were used for storage and the hoppers (on the second floor) for feeding the grain to the millstones. The grain fell through chutes from the hopper into a smaller hopper on top of the stones (on the first floor) from where it would be guided into the centre of the stones by the "slipper." a moveable wooden chute. The slipper was agitated constantly to ensure a smooth flow of grain into the stones. This was done by the "damsel" (the four-armed shaft projecting up from the centre of the stone)- so called because of the constant chattering it made against the slipper!
There are three pairs of stones at Redbournbury, two of which are encased in wooden "tuns". The third pair has been left open and unrepaired for visitors to see. The two pairs of working stones had to be found from other derelict mills after the fire since the heat and water had split the old ones. Of the original stones, nearest the staircase, the top one is made from "Derbyshire grit stone." This wears down fairly quickly, and is fit only for grinding animal feed as it leaves stone dust in the ground product. The bottom stone and both pairs of working stones are made of "French burr stone" supposedly the best quality stone, which came from only one quarry just outside Paris.
Interestingly, French burr stone is found only in small pieces - none big enough to make a complete millstone - so each stone is made of several skilfully shaped pieces held together with plaster of Paris and an iron ring heat-shrunk around the outside of the stone. French burr stone is good for milling flour because it contains crystals of very hard quartz. These create sharp grinding edges which do not chip into the flour, and the stones need less frequent sharpening ("dressing").
Each of the stones is divided into sections called "harps". The harps have a complex grinding face cut into them consisting of "lands" (the raised sections) and "furrows" (the grooves) which had to be dressed regularly using a "mill-bill", and a good eye! Once the lands were properly flattened during the dressing process. they had to be "stitched". This required up to 12 fine lines per inch to give the best grinding surface for white flour.
When the stones were together as a pair they had to be perfectly balanced, perfectly level, and precisely the right distance apart - the thickness of a piece of brown paper at the centre of the stone and of a piece of tissue paper at the circumference. This gap was adjusted by a process called "tentering;" the top stone could be lifted on the "spindle" by a turn-screw on the ground floor.
Only the top stone ("runner-stone") rotates in any pair, with the "bedstone" fixed to the floor. The runner-stone is balanced above the bedstone, hanging on the "mace" (or "rynd") which is supported on the spindle. When the grain falls into the centre of the runner-stone it is forced outwards by the pattern on the surface of the stones and the action of centrifugal force. It is crushed between the lands and falls from the edge of the stone as flour. The flour passes down a chute where it can be bagged on the ground floor as 100% wholemeal flour.
The mill is able to produce white flour. This is done by a machine called a wire-machine or "bolter". A series of sieves, made from finer and finer mesh are used to separate the 100% flour into bran, semolina, and white flour.
The waterwheel and gears
All the power for the mill stones and auxiliary machinery was provided by the waterwheel. This is 9ft 6ins in diameter, 7ft 6ins wide and is made of cast-iron for the shaft and spokes, and of wrought-iron for the 30 buckets. It is an "overshot" wheel which may have replaced an earlier 'breast-shot" one. The advantage of an overshot wheel is that it is powered by the weight of the water falling over the top of the wheel into the buckets. In a breast-shot wheel the water enters the buckets level with the axle and the wheel produces only about one third of the power of an overshot wheel. The third type of waterwheel is undershot, where the water passes under the wheel; it is the force of the water hitting the paddles that turns the wheel rather than the weight of water in buckets.
An overshot wheel needs a head of water which has to be provided by artificially raising the river. This required building the "leat" the diversion of the river along the side of the valley, until a sufficient height of water had been reached to work the waterwheel. This was a huge feat of engineering considering the mass of soil used to construct the river banks and the similar mass of clay and chalk used to waterproof the bed of the river; remarkably built by hand.
The water was built up and stored by closing the two sluices to stop the water flowing downstream. The water would fill the "launder" (or "pentrough") above the wheel which could then be opened to turn the machinery. Alternatively, if the river filled too much the sluices could be opened to allow the water downstream without turning the wheel.
The waterwheel rotates at about 10 revolutions per minute (r.p.m.) and the power is then transmitted through the wheel-shaft to the "pit-wheel" in the hurst frame. The pit-wheel drives a smaller "wallower" which in turn drives through the "crown-wheel" and "pinion", along the main horizontal lay-shaft to the three "stone-nuts." Each stone-nut is attached to a stone "spindle" which drives the runner-stone. By this stage the gears have increased the speed of revolution from 10 r.p.m. at the wheel to about 120 r.p.m. at the runner-stone.