The last rivet on the horizontal stablizer should have been a piece of cake. It was a nightmare! Plans call for a -4 and the rivet leaned a little after setting it. I drilled it out and inspected the hole. The tip rib and aft spar were just a tad off center. I should have cleco'd the ends of the tip ribs while riveting the rest of the struture. Tried moving the rib alignment with a center punch, it did not require hardly any adjusting. Set the second -4 rivet and it did the same thing. After drilling out this rivet and reinspecting the hole I decided to go one size larger by redrilling the hole to a #21 and setting a -5 rivet. This would give me a freshly aligned hole. My Cleaveland squeezer will not set a -5 rivet due to mechanical limitations of the squeezer. With the gun and bucking bar I figured it would be an easy set, it wasn't. Again the rivet started to lean. Again I drilled out the -5 and tried again, same bad result. I finally called my tech counselor and she agreed to have a look at it.
One important point to note, while drilling and punching out the first bad rivet, the tip rib end tab started to bend just a little. I tried to ensure that the pieces were tight and flush but I apparently did not get the parts trued up as good as they needed to be. This created a very small space between the two parts that I could not get perfectly straight again.
The fix - tech counselor said that it could probably go as is but we were both cringing at the thought. She suggested that we should try again, I agreed. To straighten the pieces she drilled out the rivet and then using a bucking bar and mushroom rivet set beat the parts absolutely flat and true. It only took a few hits of the gun. The next -5 went in just fine. So the very slight mis-alignment started the problem. Punching out the rivet caused more problems by bending the tab just a hair. Not getting the pieces absolutely flush with each other perpetuated the problem for an entirely different reason, same result though.
