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9th May 15. Testing Mostert's Mill under Wind Power
Article reproduced with kind permission of Andy Selfe 
Original can be found here
Last time, we tested our work after assembling the pintle bearing at the top and centralising the Lantern pinion, by turning the sails by hand.
Turning the sails by hand last time to check meshing
Today, expecting a reasonable wind, the word had gone out by Fine Music Radio that we would be 'Open for Milling'. I had other things to do on the way so by the time I arrived, all was set up with sails bent and reefed according to the expected wind.
I had indicated that I wanted to inspect the stones running close together with the tun off, either at the beginning or the end of the day. We decided to do it as I arrived. The furniture was quickly dismantled.
Removing the tun to inspect the stones from the side
The out-of-true between the stones is not as bad as I thought, however what was noticeable was that the top of the runner is very irregular. We held a fixed pointer just above it and the difference between the highest and the lowest spot was about 20mm. This is likely to cause a serious out of balance while running, and could cause the runner stone to lean one way while at operating speed.
We did another test; Neville attached little cones of Presstick to the upper ring of the lantern pinion and we turned the windshaft more than 16 turns. It is only after 16 turns that the same cog engages with the same rung again. With wind on the sails we were assured that the rear of the windshaft was fully against the thrust bearing, and the clearance between the brake wheel and the lantern at its least. Several of the cones were pressed surprisingly flat. What we were specifically concerned about was that the upper ring is very close to fouling the outer rim of the brake wheel. If we have any cause to work on the lantern in the near future, especially after having dressed the stones, we will raise the lantern away from the two supporting lugs on the upright shaft, but not too much, otherwise the upper edge will foul the steps in the clasp arms.
Brake wheel (left) and lantern pinion
When we open the stones to dress them, we plan to do a static balance test on the runner. My plan is to hang the runner on a cable using a copy of the tapered cock-head of the stone spindle. When the runner was last off, Neville took down the dimensions of the taper. His drawing can be seen on the right in the picture below. His calculations for the weight of the runner can be seen too!
Neville's sketch of the cock-head of the stone spindle and the rynd
I set about making a copy of the taper, using 6mm thick steel plates, cut to size, and welded them together. In the very centre of the small end, I drilled a hole so we can hang the runner stone on it and add weights to the light side until it balances.
Fabricated copy of cock-head taper
With the furniture all reassembled, milling began under wind power and a stream of interested visitors could be shown around. The wind wasn't steady so it taxed Adam's skill at the controls at the meal spout!
As I'm completely satisfied that the meshing problem is now cured, the next two Open Days, set for Saturdays at the beginning of June and July, weather permitting, will be set aside for Milling. Thereafter, in winter, we'll tackle the dressing of the stones which should improve the quality of the meal.
:-) A