This is the third gear in the power train of this old water wheel.
There is a cast iron, segmented, circular "rack" of 300 teeth attached to the compass arms (spokes) at about 60% out from its centre, a cast iron pinion of roughly 26 teeth engaged with this rack and the pictured driving wheel (which would have had wooden teeth for quieter running as it was inside the mill building and away from the weather, of roughly 70 teeth.
Reputed to be the largest extant water wheel in New Zealand, it appears from a date initials and a diameter carved into one of the spokes, that the wheel dates to just 1930.? No doubt the people who have formed a Trust to restore the wheel and who are about to embark on that mission, will know. The mill is now gone and it dates to the latter part of the 19th Century.
The stonework looks like it probably dates for the time the mill was erected and the main bearing blocks too may do.
The wheel is a back shot wheel with sheet steel riveted fabricated buckets attached to the cast iron shroud (rim boards) with bolts and nuts - and fitting snugly into cast-in sockets to hold the buckets in place, strengthen the bucket and render it water tight.
On a stream with good water supply a wheel like this might not have had any supplementary sealing where the bucket meets the rim - leaks would be minor and not significantly detrimental to the efficiency of the wheel but on Mill Stream I would have expected the bucket edges to have been sealed with pitch or similar as every drop of water from this ephemeral stream was precious.
The wheel ran off two races and leats with very long section of wooden fluming (as you would expect with such a large diameter wheel) jetting out from the bank behind, but they too, have completely gone.
The very earliest photos of the mill show just the one race and flume. Presumably the second race (lower down the hillside by what appears to be the diameter of the wheel) was installed and operated as an undershot adjunct to the wheel by just flowing through the wheel pit. The wheel pit is full of rubble so I cannot see what depth of backwater was usually present but the idea of a second race didn't save the mill from becoming unworkable as the stream dried up when the North Otago climate changed.
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