The National Trust has now entered its Winter season, and many properties across the country have closed completely to undertake important conservation and restoration work. One such property is Nether Alderley Mill, also looked after by the Quarry Bank team. Earlier this week the Norfolk Millwrights Alliance returned once more to carry out the annual conservation work at this 15th Century flour mill. One of our volunteers, and miller at Nether Alderley Mill, Vince Chadwick went behind the scenes…
The initial news from the Norfolk Millwrights wasn’t good; a large stone supporting the bearing for the main vertical shaft in the mill has tilted slightly, no doubt due to undermining by the running water in the mill basement. Apparently this was a fault known about when the mill was recently restored, and it was put right. But obviously the repair hasn’t lasted and the National Trust are to get a structural engineer in to have a look and come up with a better repair scheme.
The millwrights then designed a repair for a major water leak in the leat (trough) taking water off the upper wheel and feeding it to the lower wheel. After that, it was time to ‘split the stones’, that is lift the runner mill stone off the bed stone to inspect the milling surfaces.
The pit wheel for the lower water wheel is on the right. It engages with the ‘wallower’ (the horizontal bevel gear wheel on the vertical shaft), to transfer the water wheel’s power via the vertical shaft to the hurst frame (where the power from the upper water wheel and the lower one are combined) and thence to the mill stones. The vertical shaft rests on a bearing, which is located on a supporting stone on the mill basement floor (visible below the wallower in the picture). It is this support stone which has tilted, causing the bearing to wear unevenly and the gears to mesh slightly out of alignment.
The first job is to remove the ‘furniture’ from over the mill stones. The grain hopper has already been removed, and the ‘horse’ (the frame which supports the hopper) will be next, followed by the ‘skirt’, the metal shroud around the stones.
A close up view of the sweeper. As the milled grain (flour) is blown out of the gap between the runner and bed stones (there’s quite a strong airflow induced by the stones’ rotation blowing from centre to the rim along the wide grooves in the stones, like a centrifugal fan). The flour settles in the gap between the stones and the skirt. The sweeper sweeps it around the stones until it comes to the flour chute, which it drops into.
Note the metal bands around the stone, which holds the individual burr stones together in one homogeneous mill stone. The top band is very deep, and there are two much thinner lower bands. As the stone wears, the lower bands can be removed one at a time to allow the stone to continue to be used. By the time both small bands have been removed and the stone is worn down to the wide band, there is insufficient depth of stone left to continue use (above the burr stones is a deep cap of plaster of Paris; the burr stone does not extend very far up into the wide metal band). This stone might originally have had three narrow bands, one of which has already been removed.
When a runner stone is worn too thin to be heavy enough to grind the grain (they weigh about a ton when new) it might be used as a bed stone.
The flour chute. The sweeper sweeps the newly-milled flour round inside the skirt until it comes to this chute, which it falls down to be bagged on the floor below.
The millwrights fed straps around the runner stone so it could be lifted off the bed stone. The first job once the stones were separated, was to clean off the flour with brush and vacuum cleaner.
French burr stones like these are made up of sections of stone pieced together, the gaps filled with plaster of Paris. The separate burr stones and ‘dressing’ of the stones’ surfaces can be seen here. The long troughs cut in the stone carry the grain from the centre (the ‘eye’) towards the edge of the stone aided by the airflow they generate, and do the initial cutting of the grain. They distributes the cut grain over the face of the stones for even milling by the ‘stitching’ grooves. The metal object above the centre of the bed stone is the ‘mace’, which supports and drives the runner stone when it is in place above the bed stone.
The very fine grooves (the stitching) do the fine cutting (milling) of the grain while the wider ‘troughs’ do the initial cut and distribute it. On our stones some of these stitching areas were polished smooth and the millwrights used an angle grinder with a diamond tipped blade to renew them. Traditionally this job would have been done with a ‘mill bill’, a sort of wooden adze with a metal cutting tool. That was painfully slow and painful! It induced repetitive strain injuries and bits of stone and metal flying from the tool embedded themselves in the millwrights’ arm. The origin of the term ‘to show one’s mettle’ is said to originate from millers wishing to see a millwright’s fore-arm for such evidence of stone dressing experience.
In the meantime, the structural engineer and building inspector will have a look at that displaced bearing stone in the basement of Nether Alderley Mill, repairing it in time for the reopening in April next year.