In this week’s update from Priors Flour HQ I’m pleased to update everyone on teeth – thankfully, not the miller’s molars, but the re-coging of the stonenut of the West millstones in the mill!
The common arrangement to transfer power from wind or water to a set of horizontal millstones is by a stone-nut – a small cogged wheel which gears up the speed of rotation from a spur wheel which in turn is driven by the mill sails or waterwheel. At Fosters Mill, the teeth (as seen here) of the stone-nut are made of wood, typically apple wood or hornbeam. These mesh with iron teeth on the cast spur wheel. With use, the wooden teeth wear down. Eventually, they get to a point where the wear creates vibrations and at that point it is time to re-cog the stone-nut, literally, removing each wooden tooth, cutting new teeth, fitting them and then shaping them so they mesh perfectly with the teeth of the spur wheel.
Sounds simple? No, it is exacting, time consuming work and takes a high level of skill and experience. Call in the millwright!
After 30 years of service, it was time to re-cog the stone-nut on our West set of millstones, the stones we use most often on the wind. Millwright Paul Kemp stripped down the millstones so he could remove the stone spindle (on which the stone-nut is mounted) and then take the stone-nut back to his workshop. Here we see the old teeth being removed and ‘blanks’ being inserted. Each tooth goes through the casting and is held by metal wedges to keep it tight in the socket. Each one has to be fitted by hand as every socket in stone-nut casting varies slightly!
Once the blanks are fitted, working from the pitch (shape and spacing) of the spur wheel teeth, using dividers, the shape of the final tooth is marked out. Each tooth is then paired back using a chisel to the correct shape.
Once the teeth are set up, the stone-nut is fitted back onto the stone spindle (seen here). The stones are normally situated on the left hand side of what you see here – the shiny section is the section of the stone spindle that runs in the glut bearing situated in the bed (stationary) stone. Paul is here checking to see that the stone-nut is running true
Here we see the finished article back in-situ! Now we have some fettling to do to get it running smoothly and able to do another 30 years of service!
Our thanks to Paul Kemp and Cam Southcott for another great job! Photos from Paul Kemp.