Not much progress today, but I managed to squeeze the rear spar and rib rivets. For one rivet, the rib pulled away slightly, leaving a small gap. I’m not planning to drill and replace, but will get a second opinion. After that experience, I used a clamp for the rest of them and had no issues.
As I moved to riveting the skins to spar flanges, I noticed the skins are not sitting completely flush with the rib flanges, at least in some places. Given that the holes line up, I suspect my spar flange countersinking may be to blame. If the counter sinks are not deep enough, or otherwise incorrect, the skin dimples won’t fully seat in the holes. I set around 10 rivets before I stopped riveting so I can figure out a plan. It’s pretty frustrating, as fixing this would require replacing around 40 rivets, which is always risky. Here’s a picture of the gap on one side. The nearest rivet on the flange marks the first hole, which is sitting correctly, skin flush to spar flange. The rest of the holes are not flush, with a gap of around 0.025 inches (0.5 mm).
I emailed Vans to get an opinion on whether it’s a structural issue as-is. The interlocking of the countersink and dimple is designed to add strength. It’s possible this may also create stress points resulting in possible skin cracks in the future. I’ll see what they say.
Heard back from Gary at Vans, “This is not a issue from a structural perspective and it can be left as is if you wish.” With that in mind, I’ll leave as-is, since the risk of damaging the parts while re-doing is high.