I fabricated the shims that will fit between parts of the cabin frame and skin and then got started prepping the cabin frame for riveting. First up is to countersink the holes in the aft tube. The countersink bit wobbles in the hole a bit and the hole is oblong because of the curved surface, but this is expected and will work fine.
I also countersunk the holes for the outermost ears of the cabin frame stiffener. These will only be riveted to the frame, and not the skin.
Finally, I countersunk the frame for the #10 screws that attach the forward strut mounts to the cabin frame. The skin is dimpled and will sit in these dimples.
