Flush Rivet Advice

I would like some advise on flush riveting. So far mine seem to dimple the skin slightly approximately 1? diameter. They are not that bad but I have seen better. I think my tools are good, mushroom set, good rivet gun etc. I may not be using them properly. I saw a tip on Isham Tools to set flush rivets that I think might be the ticket. It uses a dimpling block to initially set the rivet and then a regular bucking bar to finish setting it. See the link. http://www.planetools.com/Dimpling Block.jpg

I do not quite understand how this works. If the hole in the dimpling block is deeper than the rivet then how does it expand the diameter and set the rivet? Or does the dimpling block just push the parts together? Has anyone tried this technique?

Thanks
Eulice Curington
RV-10 Empennage Serial # 40596

Eulice,

I've never tried the dimpling block so cannot comment there other than that it seems like an unnecessary step. Check your air pressure. I use about 40 psi for AN3 rivets and maybe 60 psi for the AN4 variety. Sometimes slightly less on either if I'm worried about dinging things. Anything more and you are likely to end up with overdriven rivets and dents (but it may also depend on your rivet gun). Make sure your driver is flush against the rivet head before pulling the trigger, and make sure your bucking bar is tight against the back side of the rivet. A common problem is overdriving - you want to pull the trigger just long enough to form a decent shop head, no longer. Most cases this is about 1.5-2 seconds at most. If you're careful, there should be no evidence of the driver on your skins.

Mostly it comes down to trying things out (maybe on some scraps rather than the real stuff) until you get the feel for the best procedure.

cheers,
greg

Try Some Paper Protection

I was getting some scuffing on the surface of the skin with my flush rivets. I starting putting some smooth construction paper between the rivet gun and the skin. It worked great. I no longer get any scuffing marks at all. The rivets lines are smooth and clean. As mentioned above, I also do a couple of short quick bursts on the gun, and use the air pressure at pretty low levels.

I like your paper idea - I have been placing a piece of masking tape over each rivet head and shooting it, and then of course have to remove the tape and put it on the next head. I can reuse the tape for about a dozen rivets before it's shredded, but it takes time to move it. Your method is faster, I believe I'll try it on my VS this week.

The dimpling block simply serves to press-form the rivet and dimpled skin to exactly the right shape, eliminating any irregularity in either the skin dimple or the rivet head, before setting the rivet. It does not contact the bottom of the rivet shank or change it's diameter - the whole point is to make the rivet head shape and the dimple shape "perfect", similar to the idea of matchdrilling.

Riveting Tape

I prefer to use regular rivet tape to hold a single rivet or a long series of rivets in place and to also protect the alclad from needless marring. You apply the tape so the clear area is over the head of the rivet. The dark green borders contain the adhesive and holds the tape into place on the skin. A roll of tape goes a long way. You can use the same piece of rivet tape over and over again until its adhesive finally gives out.

Thanks for Advise

Thanks to all who replied. I will try to monitor my air pressure more closely. The dimples seemed to be worse on the thin skins of the elevators. I have been using the rivet tape and do not have a marring problem.

Eulice

I have been using the masking tape method as well. I use the blue painters tape and it seems to come off the flush set easier. I to can get about a dozen rivets set before the tape is shredded. It is a pain but the results are good. I think I will be trying the rivet tape on the wings though. It is probably faster.

Protection is a waste of time....

..unless you are going to polish your airplane when you are done. If you are going to paint, save yourself the time and move on. Your painter, or you, will go over the entire airframe and scratch the living you know what out of it to prep. Sure, it looks nice hanging on the wall, so if that is important to you....Even if you are going to polish, the small marring from the rivet set will polish right out. I know it does not take much time to apply tape or whatever, but every little step multiplied by hundreds is that much more build time.
As far as there being a uniform dimple about an inch around the rivet, I would wonder if your dimple is not formed properly. It should be nearly impossible to do that on an AN3 rivet without telegraphing the rib or structure below right up through the skin, meaning you are hitting it way to hard. The rivet would be over set also. It sounds like you know what you are doing, so I would check your dies and/or make sure you are getting a good dimple.

I found that using a set with the urethane ring on it (ref Isham's pic in post #1) produced the best looking rivets. Don't force the gun against the work. Hold the gun square to the work with just enough pressue to keep it from sliding around. The bucking bar does most of the actual work.

Steve

Get rid of the mushroom!

Take a look at the set pictured in Peter's response and get one of those. The mushroom set is what's causing the dimple. I used a 1" mushroom set for the start of my project and got the same result. The red rubber cup set (from Avery's) completely eliminated the dimple. It's also easier to use as you hold the gun in one hand and then steady it by holding the rubber cup in the other. Much easier!

Rivet Sets

Is the set pictured in Peter's response the swivel set? If so, that set is the set I am using. From the picture on Peter's response I take it this is a two person job, especially if you are riveting with your skin horizontal. I have been using the swivel set by myself and have found it fairly difficult to control. But I was not able to hold the red tip with the other hand because I was holding the bucking bar.

I thought the set referred to in Steve's response might be easier to use because it does not look like it swivels.

I still think my air pressure might have been to high for the thin skin. An earlier reply suggested 40 psi for a 3/32 rivet and 60 psi for 1/8 rivet. Can someone confirm the pressure recommendation?

Thanks
Eulice

I have been getting very good results on my skins with a 2X gun at 40 psi, and run abou 60 psi on a 3X for the 1/8" rivets. I've been using the flat set from Avery.

Swivel Set

Is the set pictured in Peter's response the swivel set? If so, that set is the set I am using. From the picture on Peter's response I take it this is a two person job, especially if you are riveting with your skin horizontal. I have been using the swivel set by myself and have found it fairly difficult to control. But I was not able to hold the red tip with the other hand because I was holding the bucking bar.

I thought the set referred to in Steve's response might be easier to use because it does not look like it swivels.

I still think my air pressure might have been to high for the thin skin. An earlier reply suggested 40 psi for a 3/32 rivet and 60 psi for 1/8 rivet. Can someone confirm the pressure recommendation?

Thanks
Eulice

Click to expand...

Yes, the photo shows an Avery swivel set with the rubber cap. This shot was done with a helper on the bucking bar, but I have set many by myself as well. I have good results doing both. Holding everything myself is more difficult, as you have to make sure to keep the swivel set as flat as possible. To date, I feel fortunate to only have a couple of smiling rivets on the plane. Both were the result of shooting by myself, and slipping on the flush set.

Bucking Bar?

If you are denting the skin when riveting with a rivet gun, then it would seem to me that the bucking bar you are using is too light.

There are three regulars (and four irregulars) building RV's at my hangar, and we all had our own favorite steel bucking bar. That is, until I bought one of the VERY EXPENSIVE Tunsten bucking bars at Oshkosh. Now we all use my one Tunsten bucking bar. (I have to make certain I hide it in plain sight always in the same spot on the same work bench. )

I should admit that we use a 1" thick flat ground steel table top 30" wide by 40" long to back rivet the control surfaces.

Jim Ayers