Sealing of machining holes in ribs 1,2 and 3

Setting a 4.8mm rivet in a 1/4" (6.3mm) holes does not seem satisfactory. Even with the rivet tail swelling to the maximum extent, it barely fixes into this larger hole. It also causes the thin 0.63mm rib material to dish slightly, due to the fact the underside of the rivet head is also dished. The only advantage is the process is self-centering.

I have elected to set the rivet tail against 4.8mm aluminium washers. This eliminates the dishing problem. JB-Weld is used to ensure the rivet remains in position, otherwise it is held in place only by friction and the clamping force of the rivet. Centering is done manually by making reference marks.