Spring-Bow Churn: A Bow With Two Springs Keeps Its Cord Tight Round a Screw Whirl on the Crank Shaft

"The effect of these two springs on an inflexible bow is to keep the cord always at a proper tension; in a flexible bow constructed as is customary, (unless the cord is very tense) when the bow is pushed, that portion of the cord between the whirl and the hither end of the bow slackens; and when the bow is drawn, that portion of the cord between the whirl and farther end of the bow slackens; this slackening which causes a slipping and a loss of power, is avoided by my peculiarly constructed bow. The threads of the whirl keep the cord from chafing."

Drill a 13 mm hole through each side of the bucket, opposite each other, 300 mm above the inside floor. Cut a 12 mm stainless rod 450 mm long. Glue a 20 mm hardwood dowel 220 mm long into the dasher's socket, and drill 12.6 mm across its top end, 12 mm from the end. Starting 155 mm from one end, bend a crank 40 mm deep and 40 mm wide in the vise; slide the dasher rod's eye onto the crank pin before bending the second side. Pass the shaft through the bucket's holes with the crank inside, centred, and fit a collar on the short end. Seal round both holes outside with silicone sealant.

Slide the whirl onto the long end of the shaft outside the bucket, hub towards the bucket, 10 mm clear of it. Drill 4 mm through the hub and shaft, and drive in a 4 mm stainless pin cut from rod, so the whirl is "firmly attached to the crank shaft".

Cut a hardwood bow 700 x 50 x 30 mm, the patent's "inflexible bow", and plane and sand its underside slightly curved. Fit a dowel through one end as a handle, as in Fig. 1. Screw a spring-steel strip 120 x 16 mm by its inner end to the upper side near each end, outer ends free and reaching the bow's ends; drill a 5 mm hole through the bow under each spring's outer end and a 5 mm hole in each spring's tip. Pass a 4 mm cord up through each bow hole and tie it to the spring's tip, leaving enough slack between to take one turn round the whirl with the springs bent down a little.

Pour about 8 litres of heavy cream at about 15 °C, checked with the thermometer, into the bucket and put on its lid. Lay the cord in the whirl's groove with one turn round it, have someone steady the bucket or hold it between your feet, and push and draw the bow steadily, timing it. When the butter comes, take off the lid, lift the butter out past the dasher, tip the buttermilk out into a bowl, wash the butter in cold water until it runs clear, salt and weigh it.

**Abner Willson** of Colden, Erie County, New York, US 27,181, 14 February 1860, "Churn". He claimed "the bow F with springs a when constructed as described, in combination with screw whirl D operating as set forth"; he did not claim the treadles G he also shows, nor the dasher, crank shaft or vessel. His vessel is a tall wooden one; ours is a food-grade bucket, and the cone dasher, its rod and our way of fixing the whirl are ours. The patent gives no sizes; every size here is ours.