Spring-Pole Cam Churn: A Two-Arc Cam Lifts a Hinged Strip Dasher and a Wooden Spring Pole Drives It Down

"The cam p consists of two semicircular arcs, one extremity of each arc being placed at the center of the other semicircular arc, the arcs being united by their chords and the shaft passing through the chords at a point midway between the inner extremities of the two arcs." ... "On turning the shaft, the dasher is raised up gradually, and falls suddenly with the full force of the spring pole."

From 20 mm hardwood board make a box 700 mm long and 260 wide inside, 200 mm deep at the front end and 375 at the rear: cut the sides with their lower edges sloping 175 mm over the length, glue and screw the ends and bottom between them, and seal the inside joints with silicone sealant. Cut a slot 44 x 95 mm in the front end's middle, 20 to 115 mm above the inside floor, for the lever. Hinge a cover on the top and drill a 10 mm air hole t in it. Screw two front feet b, 40 x 40 mm, 460 mm long, to the sides' outer faces 160 mm behind the front, and two rear feet c, 340 mm long, 640 mm behind it, so the sides stand upright and the bottom falls to the rear. Hinge a small frame d (two legs 305 mm and a bar) to the front feet, folded up; let it down to raise the front end.

Cut five hardwood strips 20 x 20 mm, 600 mm long, and set them in two cross pieces f, 30 x 25 mm, 240 long, 54 mm apart and turned 45 degrees, so each presents an edge to the cream. Cut a hardwood lever 40 x 30 mm, 977 mm long; bore it 12.8 mm across 265 mm from one end for the pivot h, and 15 mm from that end for the pin i; saw a slot 22 mm wide from that end for 165 mm, for the roller. Screw the cross pieces under the long arm so the strips lie 2 mm above the floor when it rests along it. Pivot the lever on a 12 mm stainless pin in two hardwood brackets on the front end's outer face, 35 mm out and 70 mm above the inside floor, the long arm through the slot.

Cut a roller 40 mm across and 20 long from hardwood dowel, bore it 12.6 mm and set it in the lever's slot on a 12 mm stainless pin i. On the pin's ends outside the lever hang two hardwood pitman links 8 x 30 mm with holes 200 mm apart. Cut a spring pole 40 x 25 mm, about 1010 mm long, from straight-grained ash (the patent: "hickory or other suitable wood"); screw its rear end to a block under the bottom's rear, run it forward under the box, and hold it up on a hardwood cross piece m hung from the sides 590 mm from the front. Pin its front end between the pitman links; it should lift the lever's short arm so the dasher rests on the floor.

Bolt two hardwood arms 15 x 30 mm, 450 mm long, along the box's sides, reaching 300 mm out in front, and bore their ends 20.8 mm across directly above the roller, 70 mm above its centre at rest. Pass a 20 mm stainless shaft through them with the cam on it over the roller, held by collars; fit a hardwood crank 150 mm long with a dowel handle on one end. Set the cam so each arc meets the roller by its inner end as the crank turns.

Pour in about 15 litres of heavy cream at about 15 °C, checked with the thermometer: no more, as the patent says the box "must not be filled so full as to cover the dasher with cream when it is raised". Close the cover and turn the crank steadily, timing it: the dasher rises slowly and falls hard, twice a turn. When the butter comes, let down the frame d to raise the front end, as the patent advises, so everything runs to the rear; lift the cover and dasher, take out the butter, pour the buttermilk into a bowl, wash the butter in cold water until it runs clear, salt and weigh it.

**Alexander W. Cunningham** of West Middleton, Washington County, Pennsylvania, US 27,276, 28 February 1860, "Churn". He claimed the spring dasher worked by a cam, made of longitudinal strips presenting their angular edge to the cream, with a box deeper at one end than the other. The text calls the frame on the front feet both d and u. The patent gives no sizes or materials beyond the hickory pole; every size here is ours, our pole is ash, and our cam is printed.