Tuesday, 18 November 2014

Annual maintenance at Nether Alderley Mill

It's November again and time for the millwrights to visit the National Trust's Nether Alderley Mill, where I am a miller and a guide, for the annual check of the machinery.

Please click on any picture for a larger image.

Norfolk Millwright Alliance van outside the mill this morning

The initial news 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 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 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 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.

Once the skirt is removed, the runner stone is exposed. The 'sweeper' can seen attached to the stone. 

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 feed straps around the runner stone so it can be lifted off the bed stone 

Here is a short video of the runner stone being lifted off the bed stone using block and tackle sets.
Runner stone being lifted off the bed stone

First job, once the stones are separated, is 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. 

These 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 mill wright's fore-arm for such evidence of stone dressing experience. 

A Millbill

For an explanation of dressing mill stones, see How to dress mill stones

The steps up to the grain loft are worn by centuries of millers' shoes. One can see which foot they put on each step by the wear pattern. 

At the top of the steps (the handrail is a modern addition) the miller would step to the right (note the worn indentation in the floor) to pass between the beams and into the grain loft 

A millwright using the angle grinder to renew the stitching (very small cutting grooves) on the areas of the stones which have worn smooth

We took a look outside at the mill pond. This is the overflow, showing that recent rain has filled the pond to overflowing. 

Further round is this channel bringing water from Radnor Mere to the mill pond. It was flowing, so presumably is still doing its job. Radnor Mere was constructed by Lord Stanley to greatly supplement the relatively small mill pond at Nether Alderley, which is fed by a small steam off the back of Alderley Edge. Radnor Mere is just a few hundred yards to the south of the mill in the former grounds of ICI (later Astra Zeneca, though they are now in the process of moving to Cambridge) which was part of the Stanley estate back then. 

Mill guide Tony, National Trust staff member Katie, and fellow miller Bruce on the bridge over the Radnor Mere feeder

 The Radnor feeder enters the mill pond by a small round island. Alderley Old Hall can be seen through the trees across the mill pond.

The Stanley Memorial beyond the mill pond. It is capped by the Stanley family 'eagle & child' motif in the form of a stone statue,

The millwrights have some work to do at Styal Mill in replacing the blind for the Great Wheel, and I'll go along next week to witness that work. 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. Let's hope it can be repaired without too much delay and expense.


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