For this weeks post I hand over to Bruce Williams, one of our power volunteers, who gives us a further update on what’s been going on behind the scenes during the closed season at Nether Alderley Mill, a corn mill built in the 1500s and Quarry Bank’s rustic sister property.
As we shared with you in an earlier post, the stone block supporting the main vertical shaft and one side of the lower water wheel has shifted, such that the bearing at the bottom of the vertical shaft is wearing unevenly. In time this would do irreparable damage, so the Norfolk Millwright Alliance are setting to work remedying the faults. In order to do this, the weight has to be lifted from the stone block, which means lifting the vertical shaft, and the shaft of the lower waterwheel.
First, the lower great spur wheel (consisting of cast iron teeth mounted on an oak wheel and supported on cross shafts, which pass through the vertical shaft – bolted together with handmade bolts and angled brace struts) was dismantled and removed from the vertical shaft. Everything came apart easily, and the parts (see below) have been removed to the workshop to be renovated. The cross shafts, in poor repair, will be replaced and the oaken sections of the wheel will be inspected very carefully to ensure that they are suitable to be refitted, if not, they will be replaced. Cleaning and inspection of the cast iron gear is also planned; the bolts will be renovated, as some were bent and one or two showed signs of earlier repair.
Once the Structural Engineer had been to inspect the support stone to determine what needed to be done to stabilise it, the vertical shaft was lifted out of its lower bearing using a chain hoist, attached to one of the main beams in the Mill. The upper bearing proved to be a simple wooden block, which will be replaced with a metal bearing when the machinery is reassembled. The lower bearing was then removed from the support plate, and can be seen to be slightly oval rather than round, so has been taken to the workshop for renovation.
The main beam which held the upper bearing of the vertical shaft and stretched across the lower wheel pit was not replaced during the restoration of the Mill a couple of years ago, but was in poor condition and not fit to be used for any lifting. As this is the only possible support for lifting the lower wheel shaft, it had to be replaced, so the Millwrights made a new oak beam, and having removed the old beam, carefully lifted it into place.
Now it was possible to rig chain hoists to lift the lower water wheel axle out of its bearing, though because of the weight of the cast iron pit wheel and the water wheel the new beam was also supported with an acro prop from the wall of the lower wheel pit. In order to get the shaft horizontal, the end of the shaft had to be lifted 75mm, which is some indication of the amount that the support stone had sunk. Once the shaft was lifted, the bearing could be removed. Both the gudgeon pin on the shaft and the bearing proved to be in very good condition and will need no reconditioning.
The support plate for both bearings was then removed from the support stone, so that once the Structural Engineer has defined what needs to be done to stabilise the stone, the work can be carried out in preparation for rebuilding the mechanism.
More later . . .
If Bruce’s update has inspired you to visit Nether Alderley you can check out the web page here: http://www.nationaltrust.org.uk/nether-alderley-mill/visitor-information/