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Proud rivets on fuel tank

HeliCooper

Well Known Member
After getting the rear bulkhead on the fuel tanks and letting them harden I am noticing that most of my rivets are sitting proud. I am guessing this is from a layer of proseal in the countersink as well as my countersinks being just a tad shallow. I am wondering if anyone has any stories of using a rivet shaver. I am tempted to buy one off ebay and try and get these rivets flush but am horrified I could just ruin my tanks or make a bigger disaster than they are now. Most rivets seem to be sitting about .005 proud by feeler gauge. Some are beyond .006 and I would have to drill those out and reset them.

Additionally I have a few rivets elsewhere that are in the dimple at a slight angle making a snag. Can I drill these out and use a close end flush rivet in its place?
 
I have a rivet shaver and used it on several rivets in my tanks, leading edges and the blind rivets in my flaps and ailerons. .005" to .006" high is really high. Did you install the rear bulkhead and shoot or squeeze the rivets while the sealant was still wet, or fid you wait for t he sealant to cure before riveting?

I would definitely shave the rivets in the tank skins that have an edge that is high, I defiantly would not drill those our and install the "non structural" blind rivets in this location.
 
You are correct , these rivets sit a little proud because of the pro seal between the matting surfaces of the rivet and skin.
A rivet shaver has never worked for me.
What has worked is taking a stiff sanding block, no padding, and sand them all down. You'll end up with a perfect row of rivets and your painter will be very happy. Any part of the rivet that sits proud is doing nothing except ruin the paint job and draw your focus every time you look at your tanks.
Maybe a 320 grit and take it easy when you get close to the skins. A few scratches won't hurt. Your painter will scratch up the whole plane before painting:)
I would wait a few weeks to let the pro seal thoroughly cure.
 
shave bits

I don't know if you are aware but you can purchase a rivet shave bit for your microstructure countersink. I have used the shaver many times including my fuel tanks. Just let the sealant cure for a few months before shaving. Practice on some scrap first. High rpm works the best. Use an air drill or high rpm corder drill, not a battery powered drill.

Shavers work great, no need to fear them.
 
I have a rivet shaver and used it on several rivets in my tanks, leading edges and the blind rivets in my flaps and ailerons. .005" to .006" high is really high. Did you install the rear bulkhead and shoot or squeeze the rivets while the sealant was still wet, or fid you wait for t he sealant to cure before riveting?

I would definitely shave the rivets in the tank skins that have an edge that is high, I defiantly would not drill those our and install the "non structural" blind rivets in this location.

I installed them wet. There are only two rivets I found at an angle that I would like to fix. One on a rib and one on the j stiffener. There should be a structural blind rivet I could use I would have thought.

I know they are high. I am quite disappointed with the result but I am not sure what else I can do. When I went back and countersunk for the remaining holes in the bulkhead, the rivets came out perfectly flush. Squeezing them when wet still must have allow enough proseal to stay under the rivet head to cause them to sit proud. Additionally the .006 is not all the way around. That is on the highest side of the rivet. Many of the rivets are sitting flush on one side but proud on the other. I can only think that with the proseal over everything I wasn't able to eye the set well enough to ensure it was squeezing them flat.
 
Same row of rivets taken 180 degrees from each other.

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I don't know if you are aware but you can purchase a rivet shave bit for your microstructure countersink. I have used the shaver many times including my fuel tanks. Just let the sealant cure for a few months before shaving. Practice on some scrap first. High rpm works the best. Use an air drill or high rpm corder drill, not a battery powered drill.

Shavers work great, no need to fear them.

I have heard the shavers run in the 10-15000 rpm range. I didn't know if the air drill would be sufficient at 3000rpm.
 
On the rear bulkhead, I would drill out every other rivet and clean the dimple and squeeze new rivets. Then repeat for the second half. I actually did this on my tanks and it turned out well.

There are "structural" blind rivets available but none that are "sealed stem" like the ones used on the rear attch brackets. Even if you installed a suitable CherryMax rivet, you would still need to access the back side to dome seal the rivet. If you really decide that you have to change those rivets I would install access panels and replace them with solid rivets. After cleaning up all of the dried sealant, I ended up with two or three rivets in the ribs that were tilted with an edge sticking up more than I would have liked. I shaved them and they turned out just fine.
 
I have heard the shavers run in the 10-15000 rpm range. I didn't know if the air drill would be sufficient at 3000rpm.

I have a Dotco rivet shaver that turns 30,000 RPM. I have tried the shaver bit in a countersink cage before and it works marginally, if you feed it slow enough and spin it fast. If you can afford a real rivet shaver it would be the way to go. They are an excellent tool if used correctly. Make sure you practice on scraps that you rivet together. Start .002"-.003" shallow when learnings and sneak up on it one click at a time. Also set the stop shallow when shaving a rivet on a curved surface to avoid chewing up a skin.
 
After getting the rear bulkhead on the fuel tanks and letting them harden I am noticing that most of my rivets are sitting proud. I am guessing this is from a layer of proseal in the countersink as well as my countersinks being just a tad shallow. I am wondering if anyone has any stories of using a rivet shaver. I am tempted to buy one off ebay and try and get these rivets flush but am horrified I could just ruin my tanks or make a bigger disaster than they are now. Most rivets seem to be sitting about .005 proud by feeler gauge. Some are beyond .006 and I would have to drill those out and reset them.

Additionally I have a few rivets elsewhere that are in the dimple at a slight angle making a snag. Can I drill these out and use a close end flush rivet in its place?


Leave them alone Jim. Painter will take care of their pride unless you want it polished then it's the whole another story. Get her in the air first :)
 
I had at the same problem with the left tank. Almost all were .005+

I redid the countersinks in the right tank before fiinishing that tank and those rivets all came out between .001 to .003 proud. Well within spec.

After the left tank had cured for months, I went back and drilled out all of them. I used the every other rivet method. Redrilled the countersinks a couple of thousands deeper and then squeezed the new ones. Then the other half.

It went surprisingly quickly. I feel that shaving is just another opportunity to screw up. No need. The .001 to .003 rivets are just fine.
 
Fuel tank rivets

Jim,

When did you notice the rivets were sitting proud? Could you tell when you were first setting them? I am a few sections behind you on the wings.

Thanks, James
 
Scott, how do you guys at the factory deal with countersinking for the rivets along the tank baffle? Do you increase the countersink depth a bit to account for the proseal? I had some proud rivet heads in this area when I did my -8A tanks years ago. Used a shaver and some high build primer around that area with decent results, but still wasn't really happy with the outcome and would like to do better on my -14 tanks.

Thanks,
 
Scott, how do you guys at the factory deal with countersinking for the rivets along the tank baffle? Do you increase the countersink depth a bit to account for the proseal?

No.
The way we deal with the issue is to not rivet with proseal in the the countersink (machined or dimpled).
If proper steps are being taken to seal the tank during assembly, it shouldn't be necessary to rely on sealant under the rivet head. Especially in this location... the seal should be occurring at or very near the corner of the baffle.

We do all assembly wet and use a scrap strip of paper to scoop excess sealant out of the countersinks. Not to get it spotlessly clean, just get the majority of it out before inserting the rivet.
 
Jim,

When did you notice the rivets were sitting proud? Could you tell when you were first setting them? I am a few sections behind you on the wings.

Thanks, James

I could tell after I already squeezed all the rivets and was doing final clean up. I assumed they would sit just a little proud because I made the countersinks right on the edge of deep enough but with the proseal under them they came up. I definitely would try and follow Scott's advise on trying to clean out the countersink before riveting.

All in all I still haven't decided what to do. I feel that leaving them alone might be the best decision.
 
The shaver bits that have two flutes, or cutting surfaces work very well on aluminum rivets and produce a very smooth surface. Do not use a two flute cutter on steel fasteners.

http://www.yardstore.com/browse.cfm?viewfrom=1&catid=354&step=2

The multi-flute shaver bits work best on steel and monel blind rivets. They do work OK on aluminum rivets as well, but the surface finish will not be as smooth as the two flute design.

http://www.browntool.com/Default.aspx?tabid=344&CategoryID=140&Level=a&ProductID=2439

The diameter of the cutter will depend on the inside diameter of the shavers nose piece, or the countersink cage you are using.
 
I am yet to measure how proud they are but it is not much. I also recall that the instructions for the countersinking of the skin above the baffle say that slightly "shallow" is preferred to "too deep". I am no expert, but when I saw the RV-14 at Sun and Fun this year I also noticed that even on the factory one the baffle rivets were slightly proud.

I will be interested to see how big an issue this is. I assume all the other builders (RV-10 at least) had to deal with this as well. I am not even considering shaving them at this point.
 
I am yet to measure how proud they are but it is not much. I also recall that the instructions for the countersinking of the skin above the baffle say that slightly "shallow" is preferred to "too deep". I am no expert, but when I saw the RV-14 at Sun and Fun this year I also noticed that even on the factory one the baffle rivets were slightly proud.

I will be interested to see how big an issue this is. I assume all the other builders (RV-10 at least) had to deal with this as well. I am not even considering shaving them at this point.

Certainly there is no benefit with not shaving them down and leaving them high, unless you happen to like the look of rivet heads sticking out. Any portion of the rivet head that is sitting high and not nesting in a countersink or a dimple is not contributing to the integrity of the structure.
 
Certainly there is no benefit with not shaving them down and leaving them high, unless you happen to like the look of rivet heads sticking out. Any portion of the rivet head that is sitting high and not nesting in a countersink or a dimple is not contributing to the integrity of the structure.

Mike:
I am just afraid of damaging the tanks with the shaver, that's all. Perhaps the sanding block would help.
 
Mike:
I am just afraid of damaging the tanks with the shaver, that's all. Perhaps the sanding block would help.

I believe in you brother, you can do it! Just practice on test pieces first. If you have the shaver set up slightly too shallow, you would have a really hard time removing too much. I have gone slightly too deep with a shaver before on a curved surface when I forg to back it off a bit, and a DA sander of a scotchbrite disc cleaned it up nicely. If you don't have a shaver a DA with 150 grit will do the job as well.
 
Rivet Shaving Is Easy

There I was sweating the fact that the rivets on the rear baffle of my tank were sitting proud (by choice so that I didn't knife edge the skin when countersinking) and I was going to have to shave them. I purchased some disgustingly expensive stainless steel tape to try the "tape over the rivet and sand it down" method, and frankly I couldn't make it work. It took forever to grind through the stainless with the bristle discs I was using to start with, then there was the fact that you are trying to create a flush surface with a wheel rotating at 90 degrees to the surface. Not having a $400 30,000 rpm rivet shaver, I opted for the next best thing, my die grinder, countersink cage and Avery shaver bit. The first few rivets seemed to go ok, but the cage was getting warm because it was one of the cheap cages that has a bush instead of ball bearings, and thus couldn't handle the RPM without heating up. I had a bling bling heavy duty Zephyr one (although also a surplus steal) I purchased from Brown Tool for $14.50, but it would not fit my die grinder due to the shaft diameter, so I thought what the 'ell, I'll try it in my 1500rpm battery makita. I couldn't believe it. It worked a treat. The key was of course holding the foot firmly on the surface with your free hand, only using light downward pressure, then lifting off and clearing the chips every 10 seconds or so by hand, as the Avery bit doesn't seem to do a great job of self clearing. In all, I'd probably clear the chips about 3 times per rivet, but once I had the process down, I was averaging better than one rivet per minute, which was far faster than I could have dreamed of with the tape method.
So in a nutshell, if you've got a premium countersink cage and an Avery shaver bit, don't be frightened of having a crack at this. You can make the rivets perfectly flush with the surface. You can see in photo below a slight buffing of the skin surface on the right of the last rivet I have shaved, indicating shaving just past the perfect level, but only by a fraction of a thou. The one to the left is smack on perfect, and the one to the right is yet to be attempted. Just make sure when you start, you don't have one of those plastic boots on the rivet cage (they make it difficult getting good repeatability with the depth) and work down slowly to the desired height.
Just thought I should share this one. It feels good to have a win every now and again.
Tom.

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