A slightly frustrating work session, mostly because of stupidity. I was in the middle of riveting these two brackets that go back to back on each side of the aft bulkhead, they cleco into the big doublers and channels on the aft side. I was using AN4-8 rivets. I was almost done, only one or two to go when one rivet had unexpectedly pulled out as I squeezed, so there was no real shop head to speak of. Drilled it out -- drilling out AN-4 rivets is always asking for trouble . Couldn't get the head off so I drilled more with a #40 and then attacked from the back side only I went after the wrong rivet, and it happened to be one of the rivets that actually sits underneath the brackeets. You can't get to the head.
I ended up getting the buggered up rivet out and re riviting, but I had to abandon the "good rivet". I'll drill a hole and add a Cherry rivet nearby.