How'd you guys do this? (seat/baggage ribs & bulkhead)

This thing is giving me fits. Tonight I had to call it quits before the frustration led me to make even more and bigger mistakes.

I'm riveting the seat and baggage ribs to the F-705 bulkhead and rear spar attach bar. I had it all riveted together, then noticed that some of the baggage floor rib flanges were not tight against the bulkhead. I ended up drilling out and removing four of the baggage floor ribs. I cleaned them all up, straightened the flanges and am trying to rivet everything back together again.

So what the heck did you guys use, in terms of tools and technique, to rivet this stuff together? The first time around I used a double offset and 3X gun against a tungsten bucking bar. I know a lot of guys are against the double offset, but I have had good luck with it so far. Just not this time.

I've also tried a pneumatic squeezer (not enough room), hand squeezer (no room, won't clear the bulkhead flange, etc) and a straight set with a bucking bar. The straight set and gun seem to be the best approach, but I can NOT get the rib flanges to stay tight against the bulkhead on both sides. I'm talking about going through the baggage floor rib, bulkhead, rear spar attach bar (in 2/3 of the cases), and a seat floor rib. I can't flex the seat ribs out of the way because they're attached to F-704 on the other end.

I have a longeron yoke on the way, which may help getting access to some of them, but it seems like I need to clamp the rib flanges in places where I can't. Is this where a guy needs wing nut or hex nut clecos? I'm open to suggestions from you guys who have been there and done this successfully.

Riveting

I'm sure someone will have the answer as I'm not far behind. One trick I've used to keep parts tight is a short piece of rubber tube small enough to fit over the rivet. It need to be a bit longer than the exposed rivet so pressing on it with the bar holds parts tight till the rivet swells. Then the tube comes off and the rivet is driven the rest of the way. You probably know this. YMMV

I'm not sure in this situation, but usually when a situation like this comes up, I buck the rivet just enough for it to swell and fill the hole with a little resistance, then hold the bucking bar on the part next to the rivet and tap a few times with the gun. The swelled rivet holds the parts fairly tight, then the tapping next to the rivet eliminates the space between. Then you can finish setting the rivet.

There are 4 rib locations that use the same spar rivet holes for both the seat and baggage ribs. That means you can't avoid driving a shop head next to the thin rib. There will be some "pinching" and lifting of the flanges because of it but it can be minimized by either of the methods mentioned above (a grommet or O-ring or resetting the flange before fully driving the rivet). Just make sure the area immediately around the rivet is tight.

Good luck!

rzbill said:

There are 4 rib locations that use the same spar rivet holes for both the seat and baggage ribs. That means you can't avoid driving a shop head next to the thin rib. There will be some "pinching" and lifting of the flanges

Click to expand...

Yep. I have figured out that they probably can't be made to look perfect, but the first time around the feeler gauge would slide cleanly from one rivet shank to the next. They had to come out.

I'll take another shot at them today, probably, using a combination of methods. I think I have some old rubber fuel line around the garage somewhere. Thanks for the suggestions, guys. This has been really aggravating.

Success.

I used a combination of methods. In some spots I still had to use the double-offset, but this time I taped in in place for a little more stability. I cut a couple pieces of rubber fuel hose that I had laying around -- one is from a Vespa restoration, it's extremely thick walled stuff and very stiff. In the more troublesome cases I'd whack it a few times with that around the rivet tail to expand the shank a bit, then use the bar to "encourage" the flange to snuggle up against the bulkhead, then set it the rest of the way. A couple of the shop heads are not the prettiest I've ever done, but they're acceptable, and everything is up tight where it should be.

I told my wife this morning that I understood now why some guys build a second or third plane. She looked at me like I'd lost my mind. Of course she may be right.

Good points here as I will be starting to rivet the center fuse assembly together shortly. I have studied numerous threads and build sites and I think I'm going to approach riveting the assembly in this order to try to avoid the flanges lifting while riveting. Goal is to use the squeezer as much as possible;
1) Rivet baggage and seat ribs to the -705 bulkhead. This way you can deflect the ribs out of the way and hopefully use the squeezer.
2) Rivet the crotch strap brackets to the seat ribs
3) Rivet the seat ribs that have the crotch strap bracket to the -704 aft bulkhead
4) rivet remaining seat ribs to the -704 bulkhead
I tried different yokes and believe I can get every rivet except the middle when riveting the seat ribs to the -704 bulkhead.

That's pretty much the order I would use if I were doing this again. You'll want to drill the crotch strap brackets to the ribs (vice versa, I guess) with everything clecoed to make sure everything is square.

Oh, and... if you decide to use nut plates and screws for the seat and baggage floors as I did, drill all the nut plate holes, then assemble, THEN install the nut plates. Otherwise they get in the way something fierce.

Another way that would have probably worked in my case would have been to make a bucking bar with a 1/8 universal cup set in the end. I could have used that to buck the manufactured head, and a back rivet set for the shop heads.

I'll probably report back on the success or failure of my method for future builders as we have already passed this milestone.

Driving rivets on these types of combinations can be really frustrating. Mine is back riveting; everyone can do it but me.

Update

Method worked very well, though I still had to watch for the flanges lifting. One did lift and had to drill out and replace. But overall, good success, I find it much easier to control the quality when squeezing that driving rivets.