Since those are main rib to spar rivets, I would ask Vans before drilling.
Also, neat trick to drive those...
Place the spar flanges up on block supports on either end. Shim it so your back riveting plate with a back riveting bar will fit between. I used the tungsten bar on top for additional mass. Place a bit of rubber tube over the shank. It will allow you to apply pressure and will crush as the rivet is driven. Remove it if necessary to drive the final bit. Drive the rivets from the top. There's photos on my blog. The spar will flex the tiny bit as the rivet is driven. You may need some foam on the ends to do the end ribs as the spar won't flex at the ends.
Thanks, I actually saw your method just after I finished the rib attach rivets. meh. Should have done more background research before I started. Started on the outboard ends and they went no problem, but the longer ones through the spar doubler sometimes went awry. While some aren't pretty, I'm reluctant to drill them out of the spar if they meet strength requirements. The shop heads are fine.
I agree with Vlad. I believe there is a difference between "Structuraly Unacceptable" and not quite perfect Standard Accepted Aviation Practice. We strive for perfection, but sometimes it makes sense to leave things alone if your attempt to make it perfect could do more harm then good. This is assuming the imperfection you started out with is structurally sound but just not quite as perfect as we would like.
Agreed. Whenever I head a question like that I read the section below from the Van's manual where they cite a study by ALCO who makes your rivets.
Oliver
"The standards to which driven
rivets should conform are frequently
uncertain. In addition to dimensions
and perfection of shape, inspection is
concerned with whether the drive head is
coaxial with the shank (not "clinched") and
whether there is excessive cracking of the heads.
It has been determined that even badly cracked heads
are satisfactory from the standpoint of static strength, fatigue strength and resistance to corrosion. (Poorly set and cracked) rivet heads were tested in tension to determine how well formed a head has to be in order to develop full strength. The tensile strengths of all the rivets were within five percent of the strongest. The test indicated that minor deviations from the theoretically desired shape of head are not cause for concern or replacement. The second rivet that is driven in any one hole [is] likely to be more defective than the first because the hole is enlarged and [the] rivet will be more likely to buckle and form an imperfect head. Tests have shown that very small rivet heads are sufficient to develop the strength of the rivet shank, even when the rivets are subject to a straight tensile pull....where a large head is not needed for appearance, smaller sizes of drive head should be used to decrease the required driving pressures."
