With the dust cover now matching the drawer frame, I spent a little time today shaping the rib that will provide support to the heavy top. This rib also does double duty as an anchor for the top, to keep it flat; it will attach to the top using wood buttons inserted along the top edge of the rib, with screws securing the top.
The profile of the rib must match the flat surface, and also the 7° taper on the side aprons. I used one of the side aprons and transferred the profile to a piece of ¼-inch plywood; then I carefully cut close to the line on the band saw, and finally used a block plane to shave down to the line:
I wanted to size the rib such that the cross-grain wood movement will not pop the desk top out of position, or blow out the dust cover underneath; I calculated that 1/8-inch undersized (that is, shorter in height) will be quite adequate to account for wood movement, with a little to spare.
The following is the plywood template in place behind the center stile of the drawer frame:
Satisfied that the taper matched perfectly the taper of the side aprons, I now transfer the profile to the piece of quarter-sawn white oak that will be the rib:
Then I make sure it will fit:
Cutting close to the line on the band saw, I use the little Krenov-style hand plane I made, to size the rib to its final dimensions:
On the way back to the house, I realized I had not noticed the arrangement Sandy had made on the side of the new garden tool shed. I like it!