I left off with the bare carcase and the components for the back panel milled and dimensioned correctly. I handplane the surfaces of all the components as a final step to get the correct thickness and width along with preparing the edges. The handplaned surface becomes exceptionally smooth as any small milling marks are cleaned off. In this photo I am using a jointer plane, one of my longest planes. This provides me a perfectly straight , smooth surface. I place the back panel components on a planing board with stop, this works extremely well.
After the back panel components are sized to final sizes I need to create grooves on one edge of each rail and stile. The center stile will have two grooves, one groove for each panel. The grooves are part of the frame and panel construction and allow the two inner panels to float slightly within the frame. Dimensional changes of the two panels will then be accommodated within the frame. Frame and panel construction dates to the late middle ages and became more entrenched as furniture was placed in heated homes and buildings. Temperature and humidity variations cause wood to shrink and expand and some allowance needs to be designed in to accommodate this.
The back frame components are grooved and this operation is performed on the router table. Care is taken to orient the boards correctly against the fence of the table. I made certain to adjust the router bit to be exactly centered in the edges of the frame components. This is important in that the routed grooves will line up correctly when the frame components are assembled. The center stile will be attached differently from the outside rails and stiles.