Hollow-Arm Air Churn: A Spinning Dasher That Breathes Air Into the Cream

"The arms C' C' project from opposite sides of the lower end of the vertical shaft and their ends are sloped off obliquely as represented in order that when turned in the direction indicated by the arrow Fig. 3 a partial vacuum may be formed behind them in the cream into which the air may rush unobstructed from the hollow arms."

Print the hollow dasher upright in one piece (/uploads/blueprints/hollow-arm-air-churn-dasher.stl), with supports under the arms: a 230 mm shaft bored down its length, four air holes near the square head, and two hollow arms with oblique ends. Check the bore is clear by blowing through a top hole. Print the step (/uploads/blueprints/hollow-arm-air-churn-step.stl) and the crank arm (/uploads/blueprints/hollow-arm-air-churn-crank-arm.stl). Print in PLA at 0.2 mm layers, 30 % infill, 4 walls; wash before first use.

Bed the step in the centre of a tall wide jar's floor with silicone. Drill the lid at the centre for the shaft. Stand the dasher in the step through the lid, with its air holes above the lid, and press the crank arm on its head.

Glue a hardwood dowel handle into the crank arm.

Let the heavy cream stand until it reaches about 15 °C, checked with the thermometer. Pour in 700 ml. Turn the crank as fast as you can, the way that leaves the arms' open ends trailing, and watch for bubbles; time until the butter comes. By hand you will not reach the speed the notebook gives, so expect few bubbles: that is why they geared the shaft up with a small pinion on a large wheel. Pour off the buttermilk, add cold water, churn a little and pour off again until it runs clear; work in a pinch of salt and weigh the butter.

**Willis H. Johnson and Thomas Lewis** of Springfield, Sangamon County, Illinois, received US 5,561, dated 9 May 1848, signed 26 November 1847. The shaft turned in a bearing in the frame above the cover, driven by a pinion geared into a wheel on the winch, "the pinion being much smaller than the wheel." They held that the butter "is sooner formed than by any other known churning machine"; that is their claim. They claimed "the process of making butter by the combined action of the hollow rotary shaft and radial arms." **Honest limits.** A jar and a printed dasher stand in for their churn, and our crank turns the shaft directly, without their wheel and pinion, so it runs well below the speed at which the notebook expects air to leave the arms; the build shows the hollow shaft and oblique ends, not their full effect. The notebook's speed is an estimate. FDM prints hold food in their layer lines, so wash well and replace when worn. Your times and weights are the result.