So after last night’s back riveting debacle, I posted over at VAF to ask for help with the technique. Turns out the main issue is really cranking up the air pressure to the rivet gun. I’d turned it up a bit last night, but just a touch, like the change I make when shooting -4 rivets instead of -3s. Seems I need a lot more juice than that to overcome the extra mass of the long rivet set.

After work we went to an AOPA safety seminar, which lasted until 9 or so. After that, I decided to practice some to try and get the hang of the technique. I used a scrap stiffener angle and a chunk of my junk LE skin, drilled and dimpled them, and then tried the back riveting. I started out by shooting a few rivets agains the back rivet plate on the bench. Sending about 80 PSI to the gun makes it set the rivets much better, though even then I have to shoot for what seems like a really long time.

Once I’d set a couple that way, I clamped my practice piece in the vise and had Josie come out to hold the big bucking bar while I shot a few more, to better represent the real application of the technique. I smeared a few of those rivets, I think partially due to the work piece tending to move around and partially due to me being a little sloppy.

Bottom line, I feel way better about the back riveting technique, so we’ll give it another try tomorrow night.

I also drilled out (for the third time) that bad rivet from last night. Upon checking the hole afterwards, it was clearly oversized by this point, so I went ahead and drilled it out to #30. That’ll get a NAS1097 rivet…which should be fun to back rivet…but whatever, we’ll make it work.

I’d figured maybe I could get half of the skin-to-spar rivets done tonight, but I actually got them all done in pretty short order. Guess the tediousness of the blind rivets last night made me forget how easy it is to squeeze these things.  It took maybe an hour and a half to get all the rivets done:

Next I put the tanks in place. I’d planned on putting in most if not all of the screws and bolts, but I started with the screws at the joint with the leading edge, and here I found that there’s significant pillowing of the tank skin between the nutplates:

I know this is a fairly common problem for builders to have, so now I get to do the research on how to handle it. The only solution I recall off the bat is putting in additional nutplates and screw holes; I’d prefer to do something different if possible, since adding nutplates to those joint plates would be obnoxious now that the LEs are permanently attached to the spars.

Then I went ahead and clecoed the top skins onto both wings. If the pillowing problem doesn’t require me to delay, we should be riveting these main skin this weekend!

Update: After doing a bit of research on the pillowing issue, one thing in particular I picked up on was that having the tank fully installed could make a difference. So I went back out and installed two out of three bolts in each spar attach bracket, plus every other screw between the spar and skin. Then I retightened the screws between the tank and joint plate. The pillowing does seem slightly better, especially on the left tank, but it’s still there.

In any case, the consensus is that there’s no reason to wait on riveting the top skins. One guy even mentioned that over time, his tanks shrank or deformed a bit and the fit got better –  which seems a little odd to me, but who knows. So I’ll probably just leave this as-is for the time being and deal with it down the road if necessary. I think my most likely course of corrective action will be to try shrinking the metal in the pillowed area to pull everything in line. Some guys have installed shims between the LE skin and the joint plate to lift that skin up, but that would require drilling out rivet and generally seems like an annoying undertaking.

Went to work tonight setting all the blind Cherry rivets to hold the LE ribs to the main spar. Before starting, I labeled each rib with the rivet that would be needed. There are three different lengths of rivets required here, and I wanted to be sure I got it right:

Pulling the rivets was lots of fun. The end ribs were pretty easy, there’s a fair amount of room there. Here’s the first rib after I set all five rivets:

It got more fun from there. Except for one other rib on each wing, there’s very limited access to pull the rivets. I bought a special tool specifically for this task. That little bit of metal allows the rivet puller to sit at a slight angle for a little extra room. Between that and using the puller whose nose I ground down before, I was able to get the rivets pulled without a whole ton of trouble, though the process was kind of tedious.

And of course, on the last rivet, I messed up. Probably because I was thinking about how I was about to be done with this. I wasn’t careful with the positioning of the puller, and the rivet head didn’t sit flush against the spar:

And so began about 45 minutes of work to get that thing drilled out. First I tried just drilling it, but the bit hung in the rivet and just spun it madly in the hole. I went in for some research and discovered that knocking the mandrel out was a good first step. I managed to get that done without a lot of difficulty, but the rivet was still spinning when I tried to drill. I tried grabbing the backside of it with pliers, but doing so in the tight confines of the LE interior was nigh-impossible.

Finally I came up with a plan. I notched a piece of scrap alclad to act as a shim between the rivet head and the spar to help prevent damage. Then I used a little engraving cutter for the Dremel, which had a round head a touch larger than the hole in the rivet. I was able to use that to cut into the head until the head popped off, and then it was a matter of knocking the body out.

The anodizing had worn off the spar from the rivet spinning, so I swabbed a bit of primer on with a q-tip and let it dry a bit before setting the replacement rivet. And of course I was really careful to do it right the second time around. Much better:

So I guess tomorrow night I’ll work on squeezing the flush rivets between the LE skins and the spars. There are quite a few of those, but at least it’ll be easier than pulling those Cherry rivets in tight quarters.

Again, not much to report. Josie wasn’t feeling well again, so I came up with a plan to shoot the last few LE rivets myself. I’ve been shooting these rivets with the LE in the cradle, which means that the holes toward the edge are facing somewhat downward, which in turn means that the rivets want to fall out. So I set the LE on the workbench facing up, put all the rivets in place, and secured them with rivet tape, like I was going to back rivet. From there, I was able to use my usual technique to shoot the rivets – it actually turned out to be far easier than I’d expected.

Before setting the LE units in place on the spars, I took a moment to check the hole depths of all the LE-spar rivet holes. As I mentioned a while back, I’m going to use Cherry blind rivets in all these holes instead of trying to shoot solid rivets with really limited access. I already have the rivets I need, but I wanted to double-check the material thicknesses against the grip length of the rivets I had. For obvious reasons, I don’t want to use inappropriate rivets here…

That done, I set the LE units in place and went to work clecoing them, both through the spar to the ribs and through the skin to the spar flange. And of course, just as I was finishing this, I found a problem:

That’s the tiedown ring mount on the right wing, and somehow the skin hole is misaligned. I could swear I test-fit the tiedown ring in both of these holes, but with this alignment, I couldn’t get the ring started. Urrrgh. So I got out the Dremel with a cutting bit and carefully enlarged the hole, doing my best to try and keep it round. And there was no good way to deburr it effectively in place, so I went and removed all those stinking clecos I’d just put in, just so I could pull the unit off and spend 30 seconds deburring the hole.

The end result isn’t perfectly round, which kind of bugs me, but it’ll do. I doubt many people will ever notice this really:

I’d hoped to pull a few of the Cherry rivets tonight, but after fixing the tiedown hole, it was after 11 and so I decided to quit. As a final note, here’s the right LE unit all clecoed in place:

Finishing the LE riveting didn’t happen tonight. Josie ended up working late and didn’t feel well after that, so we’ll wait for another night. In the interests of achieving something, I ran out and primed the corners of the main skins where I filed the scarf joints.

Update: OK, that wasn’t all for the day. I remembered that I neglected to note/remember that one rivet hole I countersunk and enlarged a while back. Turns out it was one of the holes I riveted solo over the weekend, so I went ahead and drilled out the original rivet, enlarged the hole, and installed a NAS1097 rivet in its place. Along the way, I noticed a few underdriven rivets, so I hit those up a bit more with the gun.

I started out today by dimpling all the main ribs and both rear spars. The instructions say you should touch up the spar dimples with a countersink for a better skin fit, but when I did a test fit with a dimpled skin patch, I had really good fit with just the plain dimples. The instructions also warn against taking off too much material in this step, so I decided that not countersinking at all was the best choice.

Then it was time for some riveting. First I squeezed a few rivets on the spar; the main ribs that sit behind the fuel tank each have a hole on the top and bottom where there’s a rivet just through the spar and rib, which will then sit under the tank skin. Those were easy to squeeze, then I moved on to the big job – the LE units. I was mindful of the incident where I dropped a bucking bar and put a dent in my tank skins, so this time I put some old towels and rags down in the bottom of each bay just in case:

Then it was lots and lots of shooting. I got all the rivets except for the forward most three on the top of each unit – I’m going to need help for those, and since Josie was working most of the day today, I couldn’t recruit her. We should be able to get those rivets done one night this week, I think. In the meantime, I set the almost-finished LE units on the spars for a photo op:

The afternoon was still young at that point, so I decided to go ahead and start dimpling the main top wing skins and the wing walk doublers. That took quite a bit of time, but I got all the skins done, at the cost of a couple blisters. Yep, there are lots of rivet holes in these wings. But hey, dimpled skins!

At this point, I figure my evening tasks for this week will be finishing the LE skin riveting, riveting the LE units to the spars, and priming the corners of the main wing skins where I made the scarf joints earlier. Then next weekend can be main skin riveting time!

Got in some more tailwheel time this morning, came him for a nap, and didn’t get a whole ton done as a result. I basically spent all three hours countersinking all the rivet holes in the main spar. I had to take frequent breaks to rest my arm and let the drill cool off – gets a little hot when run more or less continuously…

Along the way, I noticed a small gouge in the bottom of the left main spar. Not really sure where it came from, but it was deep enough to catch my fingernail, so I got out the dremel to smooth it out before sanding and priming the area:

Tomorrow I should be able to get more done. I’d like to get all the ribs dimpled and then get started riveting the leading edge units together. By this time next weekend I might be riveting the main skins!