Back riveting wing skins...what am I doing wrong?

[N546RV]

OK, after doing plenty of research, I decided to back rivet my top skins. Got the looooooong offset back rivet set from Avery along with Andre the Giant's mushroom bucking bar. We went out tonight intending to shoot at least a few rivets to get the hang of the technique, but what actually happened is that I set precisely zero acceptable rivets in three tries.

I turned up the pressure at the rivet gun, but it still seems like I'm hitting the rivets forever and they're not deforming. And despite me holding the plastic collar on the set with my left hand, the heads are still tending to fold over instead of driving nice and square.

I've barely even started and I'm already about ready to chuck this stuff and just use a regular mushroom set and bucking bar. The back rivet technique sure doesn't seem to be the easier/more foolproof solution that some folks seem to think it is.

In fairness though, I probably should have practiced on some scrap first. Somehow I just didn't expect this to be so much of a challenge.

Side note: After a few drill outs, I'm pretty sure my first top skin rivet is going to be an oops rivet.

[BobTurner]

I am not familiar with that bucking bar, but you want one that is truly massive, unmoving. Most people use a steel plate on a massive rigid bench, or even on a concrete floor.

[crabandy]

Just a guess, but with any offset rivet set you must secure it with tape/hand pressure etc to make sure it doesn't rotate and is perpendicular to the rivet shank. I borrowed a friends back rivet set that had a small metal lip instead of the plastic collar and 1 45* bend. Not sure where the back rivet set came from but it was one of my favorites.

[DaAV8R]

I'm pretty sure that long offset back rivet set was made by the devil himself. Fortunately, we borrowed one and didn't have to suffer the humiliation of buying that thing . We used a mushroom set and a tungsten bar and never looked back.

[Arie]

Hi Philip
I also tried the long offset backrivet set ,luckily on some scrap aluminum. This was done on the bench with the normal backrivet plate ,and tried many times to set an acceptable rivet. They all looked like cr@p. I then decided that if I cant even set a good rivet with the backriveting plate ,there is no way that it is going to work for me on the skins with soneone holding the big bucking bar against the skin. I used the rivet gun with a flush set and bucked them as normal, and it came out looking great. I have since bought a long straight backriveting set from Cleaveland and used it on some scrap to test it out, this worked out perfect.
Regards
Arie

[N546RV]

Originally Posted by DaAV8R

I'm pretty sure that long offset back rivet set was made by the devil himself. Fortunately, we borrowed one and didn't have to suffer the humiliation of buying that thing . We used a mushroom set and a tungsten bar and never looked back.

Yeah, that's the way I've been leaning. It was a pleasure shooting the leading edge and tank rivets with a mini tungsten bucking bar, I dunno how I ever survived without this thing.

I think I'll Arie's approach and try some scrap/sample pieces with the back rivet plate tomorrow night, and if I can't even manage to set good rivet that way, then this back rivet set will join the annals of Tools I Bought And Ended Up Hating.

Thanks all!

[rvbuilder2002]

Like most all things in building an RV, there are processes or techniques that need to be learned, and if we try something new, it wont necessarily work the same way as other ways we were doing it.

Personally, I use back riveting in all instances that it is possible. A lot of others have done it also and got very good results.
So what is my point? If something that others have done is not working for you, it is far more likely to be the technique than it is the tools fault.

Back riveting with a long back rivet set requires a lot more rivet gun energy than traditional riveting. There are two reasons for this.
The gun is working against the mass of a much heavier rivet set, and the offset shape absorbs some of the energy.

When everything is adjusted correctly, the rivet should set in about the same amount of time they do using a back riveting plate on a table, or a mushroom set and a bucking bar.

The very first hit needs to be swelling the rivet shank and reducing the length. That is what prevents it from beginning to lean over. If the gun is set too low, it will sit there and tap tap tap, and start to lean the rivet over

I suggest you clamp some scrap in a bench vice. Turn up the gun quite a bit more, and try to get an adjustment that will fully set a rivet in about 2 seconds (3 seconds at the most). Do some practicing on the scrap before going back to the wing (The tip I have been telling people for years.... Never, ever, try something new that you have never done before, on actual parts. It is a sure way to need to order replacements, or worse)
This should give you a good starting point for the wing, then make slight adjustments as needed.
Keep in mind that back riveting is very sensitive to rivet set alignment. You must keep the rivet set very close to parallel with the rivet or you will lean them over, but having the gun set correctly, so that the rivet sets quickly, will go a long ways towards mitigating that.
Also, only push just hard enough on the rivet set to keep it in contact with the rivet. Any more than that, you risk overcoming the person with the bucking bar and it reduces the driving action, requiring you to turn the gun up even higher still.

[sbalmos]

Personally, I tried to do the same, with the wing laying flat on top of a padded table with my large back riveting plate underneath. It worked out miserably, mainly for one reason - the taper of the top wing surface from front to aft. Never made for a properly flat surface against the back riveting plate, even with other people weighing down the wing at the front to try and keep it "rotated" flat against the plate.

I resorted to hanging the wing back on my wing stand and back riveting a few rivets at a time, with my dad using my tungsten bar (my go-to bucking bar for anything in general). That way the bar always remained flat against the rivet.

[SeanB]

I used the same tools and technique you describe with a builder/friend to back rivet the top skins of my first RV7 wings. It was a challenge, but we eventually got acceptable results. It was especially difficult to get the corners where the ribs meet the spars properly set.

If I did it again....I would use low pressure, mushroom set, and the tungsten bar. IMHO, you do not gain anything but frustration back riveting the wing skins. They can come out just as smooth if done with light pressure and traditional methods. Anywhere else...yes, back rivet.

Another thought...if riveting using a traditional method...lay down some heavy padding just below the area where you are working, on the main spar...in case you drop the bucking bar.

[wjb]

Originally Posted by DaAV8R

I'm pretty sure that long offset back rivet set was made by the devil himself. Fortunately, we borrowed one and didn't have to suffer the humiliation of buying that thing . We used a mushroom set and a tungsten bar and never looked back.

+1 on the Devil Mfg. Inc. I had the same problem and never could really get a consistent product out of it. I, too, went back to the mushroom set and tungsten bucking bar and was happy every since.