Jeanne Schinto’s article “The Clockwork Roasting Jack, or How Technology Entered The Kitchen,” from the February 2005 NAWCC Bulletin, did a nice job of covering the history of these useful devices. John Disley’s letter in the June 2005 NAWCC Bulletin clarified a fine point of their operation. However, neither actually described the mechanical operation of roasting jacks. Thanks to the North Coast Regional, it can now be done.

While browsing the Regional mart, I saw a roasting jack for sale. It was placed atop a copy of the February Bulletin “jack” article. Nearby was another jack. This one was partially disassembled, and so revealed how it works.

The jack has a hollow tube on top, and is hung, big side down, from a loop at the tube end. A hook protrudes from the bottom of the big end. It is to this hook that the piece to be roasted is hung. The hook is attached to a cord that extends to the top of the tube, allowing about a foot of cord to twist inside the jack with the hanging meat. The twisting action operates a cam inside the device, at the bottom of the big canister. The cam causes a verge to oscillate and be powered by a crown wheel. The crown wheel is powered, in its turn, by a spring that is wound by the user prior to setting up meat to be roasted.

In other words, it is a verge and crown wheel escapement, with a torsional pendulum, that does the job. The hanging meat provides the necessary angular inertia, substituting as a foliot or balance wheel.