Atmospheric Combination Churn: A Fan Sends Air Down a Hollow Shaft and Out Through the Turning Arm

"By a rapid rotary motion of the hollow shaft from right to left, which is produced by the driving wheel being three times the size of the pinion, the air is forced into the fan down through the hollow shaft, while the curve of the hollow arm or paddle at the bottom of the shaft being in an opposite direction from the arms of the fan, a vacuum is created, which allows the air to be discharged, causing a vertical action on the milk or cream".

Drill a 6.5 mm hole in the middle of the bucket's floor. Push an M6 nut into the cup's trap and lay the O-ring in its groove. Stand the cup over the hole and bolt it from underneath with a stainless M6 x 16 bolt and a washer, just tight enough to squeeze the O-ring. Fill the bucket with water to check it does not leak, then empty it.

Cut the stainless tube 507 mm long and deburr both ends. Press it 26 mm into the hollow arm's hub and check you can blow through the tube and out of both open faces. Clamp the four paddles on the tube with their middles 80, 140, 200 and 260 mm above the bucket's floor, each turned 45 degrees from the one below, with stainless M5 bolts and lock nuts. Stand the arm's point in the cup.

Cut two hardwood uprights 30 x 20 mm, 366 mm long, and four bars 200 x 20 x 12 mm. Glue and screw the bars between the uprights' faces at 110, 170, 230 and 290 mm up, so the rack is 260 mm wide. Lower it into the bucket beside the shaft, the bars' middle line 25 mm from the shaft, and turn the shaft by hand: every paddle must pass between two bars.

Cut a 320 mm disc of 12 mm plywood and saw it in half. Notch the front half 24 mm across and the back half 50 mm across at the middle of the cut, as Fig. 6 draws, and bore a 24 mm air opening in the back half 90 mm from the middle. On the front half screw a hardwood block 80 x 56 x 30 mm over the notch, bored 17 mm for the tube, and two bearing blocks 44 x 30 mm, 110 mm tall, their near faces 45 and 115 mm from the middle, bored 12.6 mm through 90 mm up. Slide a 190 mm stainless rod through them for the crank shaft, pin the driving wheel on its inner end and a hardwood crank arm with a dowel handle 88 mm out on the other.

Lay both cover halves on the bucket, the tube through the journal. Pin the pinion on the tube so its teeth mesh fully with the driving wheel, just above the journal. Glue the fan's two discs together, arms between, and clamp the fan on the tube's top. Turn the crank: the shaft turns three times for each turn, and you feel air drawn in at the fan's rim.

Pour about 10 litres of heavy cream at about 15 °C into the bucket, checked with the thermometer, and put the cover on. Turn the crank steadily, faster than the notebook's lowest speed, and time it. Lift the back half now and then to look. When the butter comes, lift the shaft and rack out, pour off the buttermilk, wash the butter in cold water until it runs clear, work in a pinch of salt and weigh it.

**William Smith Hall** of Quincy, Massachusetts, US 24,934, 2 August 1859, "Churn". He claimed forcing a current of air through the milk or cream by the rotary fan combined with the upright hollow shaft, the rotary hollow and solid paddles and the stationary bars. He gives no sizes but the driving wheel three times the pinion, so every size here is ours: a crown wheel and pinion stand in for his wheel and pinion, and the fan, arm, paddles and rack are printed or cut to fit a 20-litre bucket. Our notebook is a rough upper-bound estimate, not a test.