There’s nothing particularly complicated or exceptional about the construction of the table’s frame other than possibly, the (aforementioned) upper gate pivot.
After drawboring all the joints, I assembled the gates (securing the rails to the stiles with 1/4″ oak pegs) before incorporating them into the table’s frame and pegging it too (fig. 1).
Fig. 1. The assembled table frame.
Fig. 2. The gates operate within the frame.
Fig. 3. Shaped upper end rails.
Fig. 4. Braganza feet.