Those gaps, always the gaps

John Courte · #1 11-04-2005, 08:58 AM

Hi all,

I'm riveting the middle rib to the forward spar of an RV-7 VS, and for some reason, I can't seem to drive the rivet without making a gap between the rib flange and the spar. Why does this happen? I have the other two holes clecoed down, and I even clamped the flange to the rib for good measure. And here's the kicker: I'm doing this with a pneumatic squeezer! What is it about my technique that causes the rivet to somehow find a little foothold to expand between the flange and the spar, making an unacceptable rivet? I also did this on one of the HS end ribs, resulting in a fairly ugly workaround. I'd like to figure out how not to do it again.

-Desperate in Los Angeles

cjensen · #2 11-04-2005, 09:05 AM

is the hole fully deburred? maybe a small piece of aluminum or other debris in between the flange and spar web?

maybe try riveting with only one of the other two holes cleco'd, and clamp the other side. maybe the three holes aren't lined up with two clecos and a rivet in place. that may cause the metal to lift a little when pressure is applied.

make sense?

mgomez · #3 11-04-2005, 09:11 AM

I agree with Cjensen...it may be that the part is overconstrained.

That's geek-speak for the fact that two points define a straight line, and if you try to add a 3rd point, if it's not exactly on the line, it'll force the line to be crooked.

Try to cleco on one side of the hole. Drive your rivet. If I'm right and this is the cause, then a hole on the OTHER side of the rivet will be slightly misplaced, and you'll have to redrill it to fit ITS rivet.

Hope this helps,
Martin

Radomir · #4 11-04-2005, 09:17 AM

not sure if it's possible in this particular case, but have you tried flipping the rivet around? and squeeze it the other way around..

I can't really even remember how these parts look.. been too long

Steve · #5 11-04-2005, 09:29 AM

Verify the flange on the rear of the rib is flat ensuring full contact to the surface of the spar prior to riveting.
Steve

John Courte · #6 11-04-2005, 09:30 AM

I think flipping the rivet around is probably my next option, but the overconstraint makes sense too. Thanks for the help!

alpinelakespilot2000 · #7 11-04-2005, 10:12 AM

John--

Make sure the factory head of the rivet is on the thinner material. What it sounds like is that you've got the rivet head the other way around. General rule of thumb--unless "looks" dictate--always put the factory head on the thinner material. If you do it the otherway the shop head tends to deform the thin flanges. I wouldn't spend too much time drilling them out, if at all (you'll probably do more damage than good) but on future ones try to follow the above.

If you already did the above, keeping the parts tightly together while riveting is my only other suggestion. My wife often holds the flange against another piece with a small screwdriver while I squeeze it.

Good luck.

Steve

jcoloccia · #8 11-04-2005, 10:18 AM

I found that most of the flanges on my ribs have a bit of a curve to them. Sometimes it doesn't matter, but with the longer ones I had to staighten them out to get a decent fit. When I didn't straighten them out, I had the same exact problem you're having and had to drill a couple out.

Maybe this just happens on the occasional rib for some reason. I only noticed the problem a couple of times.

vlittle · #9 11-04-2005, 11:04 AM

One technique I have used to prevent this is to slit a small rubber grommet in half, and slide it over the buck tail of the rivet you are trying to set.

Partially squeeze or drive the rivet. The grommet will be compressed during riveting, forcing the flange against the spar, taking up any gap for the rivet to squeeze into.

Remove the grommet and finish driving/squeezing the rivet.

Vern Little
RV-9A

rzbill · #10 11-04-2005, 01:50 PM

I also use the technique espoused by Vern. I had some rubber washers samples of various durometer values (from some salesman, for sure) in the shop. After following the other rules about manufactured head placement on the thin material side, if there was still a gap, I use the rubber over the tail of the rivet. Squeeze the rivet a little to lock the parts together and then remove the rubber to finish the squeeze. Same technique works on a bucking bar, too.