Today was a long back rivet session. To pick up where I left off I decided to use the long bucking bar used on the elevators and mount it on the other corner of the table to get those hard to reach rivets while back riveting.
Couple tips:
1) Set one rivet then check that it's flush. If one is high, they will all be high (learned that the hard way)
2) Remove every cleco. Sounds weird but those clecos can do more bad than good. Instead of relying on clecos, get the rivets taped in and lined up on the back rivet plate or bucking bar and use a clamp to make sure it's flush.
3) TRIPLE check that your angles are completely flush before setting. When I noticed a sliver of air between the dimples on one of the angles I pulled out my “dimple” checker and noticed that two of my counter sinks were not deep enough to fully allow the angle to set flush. So I rechecked them all and luckily only had to counter sink two holes total (since I had already primed this wasn't perfect but I put some alodine over it).
4) If you are going to use the bucking bar you need to make sure the rivets in the center. Don't try and do both lines. Just do one line, unclamp, move it over a little and then do the other line. I also used a wood shim to maintain the edge distance and kept checking that the rivets I was doing were in the middle of the bucking bar (see picture).
5) I had to use a long mushroom tip to get those deep ones where the angle interferes with the back rivet set. I don't have a long back rivet set. Although I had to set them longer, I found that the quality of the rivets were very good.
6) Do the gussets last. They are actually the easiest ones to do.
Hope this helps someone else down the road. I'm glad I took time to think this over. I've seen blog's where people used the C-frame for this section. That wasn't necessary at all in my experience. I recommend just using the back rivet plate, the long bucking bar and plenty of patience. This is not the time to rush 😉.