In Power Volunteer Bruce’s last blog about Nether Alderley Mill, the important restoration work was part way through and a tremendous amount of work was being done. Bruce continues the story here.
We left Nether Alderley Mill with the vertical shaft lifted out of its bearings and supported on a chain hoist, and the lower water wheel axle lifted 75mm and also supported on chain hoists.
Since then, a block of resin based cement has been installed on the top of the support stone both to raise and to level the bearing surface. This cement, when fully cured, can support around 60 tons, so should cope with the weight of the mill machinery – about 5 tons for the lower water wheel, probably slightly less for the vertical shaft when fully rebuilt.
In addition, further to stabilise the support stone, holes were drilled in it to a depth of 1.5 metres into the bedrock, and 30 mm steel bars were inserted and grouted into place so that the stone should not be able to move again.
Meanwhile, back in their workshop, the Norfolk Millwright Alliance had been working on the various items removed to renovate where possible, repair where necessary, and prepare replacements where the originals were beyond repair.
Also, while waiting for the work on the support stone to be complete, the millwrights installed a new pentrough (a trough made of wooden boards which carries the water) for the lower wheel, as the old one had let more water fall onto the back of the wheel than went down to drive the wheel!
They also installed a spillway below the pentrough, in order that water deliberately spilled to prevent the wheel from turning, is now directed away from the wheel – this will make the mechanism much more efficient.
Now for the reconstruction! First the support plate and the bearings for the lower wheel and the bottom of the vertical shaft were refitted on the new, level, surface, and the waterwheel axle bolted into its bearing.
Then the vertical shaft was carefully lifted into its bearing and delicately moved, millimetre by millimetre, until the wallower engaged properly with the pit wheel, and the shaft itself was exactly vertical.
The new top bearing was then fitted to the new beam, and the vertical shaft was fixed and ready for the next stage.
The original compass arms which support the great spur wheel were both broken, so new ones have been made from oak.
In addition, the wooden sections of the great spur wheel have been repaired. There were many holes through the sections, which indicated that in the past the iron track plates had been moved on several occasions – all of these had to be filled.
Where necessary, damaged sections were replaced with new oak so that when the wheel was replaced it would be possible to get it exactly circular.
Once the sections had been bolted together, they were then bolted to the compass arms, and the careful work to measure what needed to be done to get it both circular and horizontal started. In one place a few millimetres needed to be removed from the circumference, but in another a fillet had to be made to increase the circumference by about 20 mm in the middle, tapering to nothing at the ends.
The track plates could now be fitted – these were carefully spaced so that the gap between the teeth was consistent all round, which had not been the case before it was dismantled.
As these teeth engage with the vampire gear (which transfers the drive from the lower wheel to the shaft driving the mill stones), it was also necessary to lift the vampire gear to accommodate the fact that the great spur wheel is now higher than it was. The axle of the vampire gear is now horizontal, rather than sloping down towards the great spur wheel.
It would be good to report that that was the finish – but on testing the mechanism when being driven by the waterwheel, it was found to be not quite right – so the track plates came off again, the great spur wheel was further modified, the track plates refitted.
On further testing, it was still not quite right, so the cycle was repeated until it was deemed to be as good as it could be. The mechanism now runs much more smoothly, much more easily, and much more quietly than it has ever done, so the millwrights can be proud of their attention to detail, and their determination to “get it right”.
Unfortunately the mechanism was completed only on the Tuesday before our season opening day on Thursday, so it has not been possible to set up the millstones in order to be able to mill grain into flour yet – but this will be done as soon as possible.
Nether Alderley Mill is open on Thu, Sat and Sun from 1-4pm until October