Both horizontal spars are ready for ribs. The aft spar has brackets (left) in addition to the doubler (center and right). I'm showing both sides of the riveted doubler below.
The forward spar includes the spar caps. I cleco'd the heck out of those when riveting to make sure they fit good and tight.
I did make a mistake and riveted in a universal head where a flush head rivet was called for. Removing that was interesting since that countersink could cause trouble. So I used my pin punch to start the hole, then drilled down flush to the spar with the following sequence of bits: 1/8", #42, #40, #36, #33 and #30. I took that cautious approach to be sure my hole was centered. When I popped off the manufactured head, I was greeted with a perfect sight (left). I wacked the shank a few times with my 1/8" pin punch and the thing wasn't coming out. I figured, since there were three thick parts being held together, the shank may have a non-uniform diameter. So I decided to snap off the shop head too, using the same sequence of drill bits as before. That was the first time I've removed a shop head. Nothing to it. Turns out, still couldn't get that shank out. So I started drilling out the shank's center to relieve the pressure. It took up to a #33 followed by the punch to get it out. Notice the shank's non-uniform diameter (right). This is why it was so hard to get out!
Forward spar with its caps and doubler, both sides.
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