Double Rotary Crag Churn: Two Shafts of Four-Edged Arms Turn Through Each Other in Twin Half-Cylinders

"As these pinions c, c, are both driven by the common wheel b, such pinions and their shafts will have rotary motion in the same direction so that as the arms on one shaft go down, those on the other shaft will pass upward, and the arms or dashers will thus be continually passing each other, giving the most complete and perfect agitation to the milk in the churn."

Draw two circles 280 mm across, centres 200 mm apart, on 20 mm hardwood and cut two ends to that outline. Rout a rebate on the inside of each to the 243 mm circles for the sheet, bore 16.6 mm at the two centres, and saw each end across through the centres: the lower halves carry the trough, the upper halves the cover. Bend 1.5 mm stainless sheet, 400 mm long and 615 mm round, to the two lower arcs, and screw it into the lower rebates with silicone sealant. Make the cover A the same way on the upper halves, with two short stainless air pipes a. Fit a spigot J at the bottom of one end, where the two arcs meet.

Screw four legs 30 x 20 mm, 270 mm long, to the ends, a cross board shaped to cradle the trough, and two rails underneath. Make the draw H a hardwood tray 360 x 300 x 70 mm that slides on the rails, with a sieve l of stainless mesh on a frame inside it.

Cut two 16 mm stainless shafts 495 mm long. Thread six crags on one and five on the other, 70 mm apart, so the five sit midway between the six, and turn each set a quarter turn from the last; pin them. Lay the shafts in the ends' half-holes, hold them with shaft collars, and put the cover on. Pin a pinion on each shaft's geared end, 25 mm outside the end. Bolt a bracket to the end, fix a 20 mm stud in it 66 mm above the shafts, and fit the wheel b on it meshing with both pinions, with a crank and handle.

Pour about 12 litres of heavy cream at about 15 °C into the trough, checked with the thermometer, and put the cover on. Turn the crank steadily, timing it. When the butter comes, draw off the buttermilk by the tap into the draw; shake the sieve to gather the bits of butter and put them back. Take the butter out, wash it in cold water until it runs clear, salt and weigh it.

**Aaron S. Cornell** of New York, US 26,093, 15 November 1859, "Rotary Churn". He claimed "the arrangement of the rotating shafts armed with the concave or recessed crags or dashers within the two concave or half cylinder chambers placed back to back". His crags were galvanized iron or metal; ours are printed. His pinions screw on with left-hand threads so that turning the wheel backwards takes them off; ours are pinned. The patent gives no sizes; every size here is ours.