I left off with four carcase panels which needed to be dimensioned and flattened to exact and uniform thickness. At this point, the panels are roughly at the final thickness and ready to be hand planed for a smooth, uniform finish across the complete panel in both width and length. I use an accurate solid steel straightedge to determine the high spots on the panels, this after a final check with winding sticks to check for any small, remaining twist. The process I use is to slide the steel straightedge across the width of each panel along its length and marking with a pencil any dips or bumps or any cupping. Since each of these panels is approximately 14 inches wide, there is bound to be some irregularity on the surfaces until I hand plane these surfaces. Each side of each panels is flattened similarly with the final thickness of each board constantly in mind. The final thickness, in this case 11/16 inch, needs to be accurately maintained throughout the panels, both across the panel and along the length of the panel. I have made a few passes with a long jointer plane with a long bearing surface to make quick work of any bumps and hollows over the length of the panels.
Afterwards, I switch to a smoother plane and smooth the panels further until the high and low spots disappear, all the while I reducing the depth of iron in my smoother plane to take progressively lighter shavings. I'm also using my widest smoother, No. 4.5, for this application, this provides less overlap in the plane strokes and covers more area quickly. A stick of wax is your friend when doing this type of work, this keeps the hand plane gliding smoothly and somewhat effortlessly. When I assembled the panels from boards earlier I made sure to orient the grain of the boards in the same direction, this decision is now obvious as a wise decision since hand planing can be accomplished in the correct direction.
Once I have a rhythm established, flattening these panels is actually an enjoyable task. Tearout is non-existent since I'm planing with the grain and the beech panels are fairly tame, so all I get is nice, fluffy shavings. I had to watch myself to not get carried away. At this time, I have four panels hand planed to thickness (uniform thickness) and perfectly smooth , as determined from some final checking with the solid steel straightedge.
Next I will dimension each of the two side panels and the top and bottom panels to the final width and length which the design calls for.