- Modified the inboard fuel tank rib by cutting out the access hole using a flycutter on the drill press. (DANGEROUS TOOL!!) - Drilled the screw holes and deburred - Drilled nutplate holes, deburred and dimpled the rib where flush rivets fit. - Machine countersunk the T-407 stiffener ring nutplate rivet holes to accept the dimpled rib. - After riveting one nutplate in place, found that machine countersinks were not deep enough to accept dimpled rib. Will correct tomorrow.