With the top guides and racks “installed” (…and by that I mean in place in the carcass. At this point, they are not actually fastened to the carcass…), the spring barrel drive mechanisms are the next components to be addressed. These two devices, mounted on each side of the main box, provide the power to make the table open.
The pinnacle of high technology during the eighteenth century, the drive mechanisms are based on clock mainspring barrels. Holes in the exterior of the aprons admit a key to tension them, just as one winds a clock. Since they engage both the upper and lower racks, their placement within the carcass aprons is critical. The image shows the layout lines defining where the mechanisms will go. But it’s not just a matter of simply excavating the material. The depth of each component is important since the racks, and drive gear teeth must align.
I will be excavating the material, and installing these mechanisms over the next week. I anticipate there will be a number of adjustments required. Holes will need to be bored in several stages, mirroring the various diameters of the mechanism followed by mortising.