The next (and probably most frustrating) part is the mechanism on the back. It works like a beach chair to hold up the top of the table. We used the spruce and birch pieces like so:
As you can see, we put three spruce pieces together to make the bar that holds the light fixture in place. You can't see in the pictures, but afterward we used the bolts and washers to let the bar rotate.
We didn't attach it right away, since we had to put the table itself together. Once we had tapered each of the legs, we routed out strips from the two internal sides in order to create a mortise and tenon joint (or, more like a Bridle joint that doesn't cut all the way through the female edge), deep enough to allow the spruce pieces that would form the body of the desk to fit snugly inside. We glued them (and needed a little wood putty to finish it up). After cutting the sides and creating the two inside pieces with four notches apiece (for the bar on the back to rest in), we glued the legs and sides together, clamped it all, and let it sit for a few days to dry.
That's the end of part III. Part IV coming soon!