So I got a question for someone. I?m about to start on my tanks and before I do I wanted to practice ?Wet Riveting? and also I want to see how the Substructure and Tank Dimple Dies looked compared to the regular dies. I have to say I?ve gotten pretty good at setting rivets since starting on these kits but out of the 20 ?Wet Rivets that I was practicing on around 12 rivets were not set square to the surface which leaves one edge of the rivet above the surface. The rivets are in the hole at an angle and with all the Proseal in the way the rivet doesn?t want to lay flat in the dimple so I?m having problems setting them square. Also I believe the Substructure and Tank Dies leave a deeper dimple then what?s needed. First of all I?m going to stick with the regular dimple dies for my tanks but any tips or tricks on how to get the rivets to lay flat or square to the surface with all that proseal in the way?
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"Wet Riveting" Tank Question
- Thread starter cwharris
- Start date
To get a perfect rivet, you must wipe the ProSeal off the soon to be formed Shop Head. Keep the bucking bar clean also. Yes it may be two extra steps per every rivet. Clean rivet shank (soon to be formed shop head) and the bucking bar. Yes the rivet gun rivet set also needs to be kept clean.
wirejock
Well Known Member
Tip
Yep. Short and simple.
Lots of tanks were and are built with standard dies. I used the tank and SS dies and was pleased with the results.
Yep. Short and simple.
Lots of tanks were and are built with standard dies. I used the tank and SS dies and was pleased with the results.
I have to agree with Tom023. Why do we need to apply pro seal wet in the dimple if afterwards we apply pro seal to the shop head? Wouldn't that be enough to seal the rivits?
You don't.
If you are desiring the best outside finish on the tank, excess sealant should be removed from the dimple before inserting the rivet ( it doesn't have to be spotless ).
What I do described HERE
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N941WR
Legacy Member
I agree with Scott. The only thing additional I would recommend is to use riveting tape on each rivet and remove it as soon as the rivet is set and DO NOT wipe any pro seal off the tanks, rivets, etc. with MEK or any other solvent. You can sand excess pro seal off your tank after it hardens.
Thanks guys. I believe I can get the best rivet set if I don't use pro seal in the dimples. That's good to know that we don't need seal in the dumples. Thanks
Why shouldn't excess sealant be wiped off of the tanks?
N941WR
Legacy Member
The MEK can penetrate the pro seal and cause paint blisters down the road, even though the tanks passed the balloon test.
I cleaned the top of my left tank with MEK and that is the only place where I had paint blisters. Everywhere else I sanded the excess MEK off.
PS. The blisters didn't show up until a year after I had the plane painted.
The MEK can penetrate the pro seal and cause paint blisters down the road, even though the tanks passed the balloon test.
I cleaned the top of my left tank with MEK and that is the only place where I had paint blisters. Everywhere else I sanded the excess MEK off.
PS. The blisters didn't show up until a year after I had the plane painted.
Got it. Just to be clear though, wiping any rivet rows with MEK prior to paint without allowing the MEK to gas off will cause paint blistering. The MEK does not affect the integrity of the fuel tank sealant and will not cause leaks.
N941WR
Legacy Member
Not correct. There was months between cleaning off the MEK and the paint. I would not touch the tanks with MEK after you have set the rivets.
Your plane, your choice, but if I had to do it over again, I would not get anywhere near the tanks with MEK after they were sealed!
Just one guy's experience, you may have different results.
I hear what you are saying, and i understand that you believe that wiping the rivet rows caused the blisters. I do not know what caused the paint blisters, but it was not the MEK unless you wiped it and didn't let it dry thoroughly.
I can tell you from experience that MEK is used to clean excess sealant from rivet heads, Hi-Lok heads, Hi-lites, bolts, etcetera during manufacture of heavy aircraft.....and it does not affect the integrity of the sealant or cause leaks.
N941WR
Legacy Member
I wish I could believe you but my experience is different and since we are dealing with a bunch of first time builders, my recommendation is to NOT clean off excess pro seal with MEK but rather let it dry and sand it off later.
I agree with the rivet tape and the frequent wiping and cleaning of the tools and shop heads, but I used tank dies and a toothpick to make sure there was a precise and small amount of sealant in every rivet hole. My tanks came out fine. the sealant will squeeze out during setting, you will get a metal-to-metal set. The sealant just fills the gap and adds that last bit of security to prevent leaks.
My tank dies are not much deeper than the standard dies. The rivets are still slightly proud due to the thicker skins. Each has a slight ring of sealant around the heads, that's all.
It's the out dent from dropping the bucking bar, and one rivet gun smile that lets everyone know, "Yes, I did build this airplane!"
I think paint blisters are caused by gasoline leaking thru rivets that were not set with sealant. every blister I have seen is directly over a rivet.
My tank dies are not much deeper than the standard dies. The rivets are still slightly proud due to the thicker skins. Each has a slight ring of sealant around the heads, that's all.
It's the out dent from dropping the bucking bar, and one rivet gun smile that lets everyone know, "Yes, I did build this airplane!"
I think paint blisters are caused by gasoline leaking thru rivets that were not set with sealant. every blister I have seen is directly over a rivet.
I agree.
I have cleaned the exterior of all the RV tanks I have built over the years (at least 15 sets ) built with proseal and flame master sealants, and I have never had any paint blisters.
I do not know what the cause is, but I feel confident that it is not the result of wiping with MEK or acitone after assembly.
When standard dies are used on .032 skins (same as a fuel tank skin) in areas other than the fuel tank, properly set rivets are totally flush with the skin surface.
So if you have rivets on the fuel tank that sit slightly proud when you used tank dies, it is because there is sealant between the rivet head and the inner surface of the dimple...
Maybe the cause for the paint blisters is due to too many builders following the terrible advise of assembling the tanks with clecos, then letting the sealant cure prior to riveting. This process is how you make a form in place gasket, not how you assemble primary stucture.
If you let the sealant cure prior to riveting, the excess sealant will obviously not get squeezed out and you will have built the tanks with a polysulfide shim between the structural parts. Add 125 Lbs of fuel inside of the tank and the wing bending loads and it's no mystery why some builders tanks have loose or weeping rivets. I have read multiple posts on this site where builders/owners are "factually" stating that all RV tanks will leak in a few years time. I don't buy it! I owned a 1969 PA-28-180 for 10 years that had tanks that didn't leak or even weep around the first rivet, and these tanks were never resealed. I have maintained many other wet wing light piston aircraft that do not leak and have never been resealed. Furthermore I have worked on hundreds of heavy aircraft that actually pressurize the wet wing stucture that do not leak. In the off chance you do experiace a leak or weep in a wet wing structure it is always due to a workmanship issue such as improper fastener hole diameter, poor preparation prior to sealant application, voids in sealant coverage at structural seams etcetera.
MEK and Acetone do not cause tanks to leak. I bet we would see a dramatic reduction in reported tank leaks if we could get everyone to assemble thier tanks correctly.
If you let the sealant cure prior to riveting, the excess sealant will obviously not get squeezed out and you will have built the tanks with a polysulfide shim between the structural parts. Add 125 Lbs of fuel inside of the tank and the wing bending loads and it's no mystery why some builders tanks have loose or weeping rivets. I have read multiple posts on this site where builders/owners are "factually" stating that all RV tanks will leak in a few years time. I don't buy it! I owned a 1969 PA-28-180 for 10 years that had tanks that didn't leak or even weep around the first rivet, and these tanks were never resealed. I have maintained many other wet wing light piston aircraft that do not leak and have never been resealed. Furthermore I have worked on hundreds of heavy aircraft that actually pressurize the wet wing stucture that do not leak. In the off chance you do experiace a leak or weep in a wet wing structure it is always due to a workmanship issue such as improper fastener hole diameter, poor preparation prior to sealant application, voids in sealant coverage at structural seams etcetera.
MEK and Acetone do not cause tanks to leak. I bet we would see a dramatic reduction in reported tank leaks if we could get everyone to assemble thier tanks correctly.
Hey Mike H
Now I?m getting more nervous about starting my tanks because that?s what I was thinking about doing. So we don?t need to assemble the tanks with clecos while the proseal is drying? Since this will be my first set of tanks to build, how do I set all the ribs in place and set all the Rivets for those ribs all before the proseal dries on me? Please correct me if I?m wrong here but if we only work with one rib at a time meaning apply the sealant, place the rib & then set the rivets how do we slide the other ribs in place without messing up the bead of sealant?
Do I need to use Substructure and Tank dimple Dies or the regular dimple dies?
Also I know you are primering the Exterior skins but did you primer the exterior of the tank skins before you started assembling the tanks?
Kyle Boatright
Well Known Member
Here's how I did it 16 years ago. Still leak proof today:
Assemble your tank in the tank fixture. Then make up enough proseal for one rib. Remove and butter one rib, put it in place, cleco it, then rivet it. Lather, rinse, repeat, completing one or more ribs each work session. Then, if you want, you can add proseal over the shop heads. At some point in the process, you apply a filet of proseal along the inside of the joints where the tank end ribs join the tank skins.
I would not externally prime a tank skin before attempting to seal it.
To add....a careful survey of builders with blistered tanks showed that MEK usage was not a common factor.
The polysulfide shim also tends to be created in the case of "extra depth" dimples and countersinks. That shim is not solid rubber.
DO NOT cleco the tanks together and wait for the sealnt to cure prior to riveting. Use regular dimple dies. I applied the Akzo 463-12-8 solvent resistant primer to the exterior after the tanks were complete and held air for a few weeks.
Mix a small batch of B2 sealant that will be used to install the stiffener angles. Place the mixed sealant on one end of some clean cardboard and transfer a small amount to the center. Use a sealant roller and roll out the small amount to achieve an even thin coat on the roller surface. I prefer a rubber surface roller. This roller can be cleaned with acetone and reused multiple times https://marshalltown.com/2-flat-commercial-grade-solid-rubber-seam-roller-durasoftr-handle.
If you work fast, or you have a riveting partner you can shoot all of the stiffeners in before the sealnt starts to set and gets too thick. If working by youself, only mix a couple of ounces at a time and work untill the sealant starts to set, that way you don't waste lots of sealant. Same process for the ribs, with a riveting partner you can install all but the two end ribs of one tank using one batch of sealant. Start with the inboard most, or middle rib, then alternate working outboard.
Now that you have a even coat of sealant on the roller, you will use it to apply an even, thin application of sealant to the mating surface of the stiffener angles. There is no need to apply the sealant to the skin and the angles or ribs, application on one surface provides ideal sealant thickness. It is way easier and much less messy to roll the sealant on the rib and stiffener flanges, there is no need to mask the parts as you would if you applied the sealant to the tank skin. Using a roller to apply sealant will result in an even application ranging between .005" to .020" depending on technique and applied roller pressure. If you prefer to have some sealant in the rivet holes you can apply the initial coat, then turn the roller sideways and lightly drag the edge of the roller down the part to smear some sealant in the rivet holes, then run the roller across the part again to smooth out the seant. Remember, "bigger the glob, better the job" is not what we are looking for here. As long as there is an even thin coating on the flanges, you will have sufficient squeeze out when the rivets set and draw up the structure. Keep in mind that the sealant application is only effective in the leak path area. This means that 1/8" fillet seal that that many builders blob on the the interior ribs is not really doing anything becuase during the riveting process the thin fay sealant application was squeezed into the rivet hole and out around the flanges of the rib sealing the only possible leak paths to the rivet head. Also an excessive amount of sealant in between the structural components will weaken the stucture by allowing the structure to flex, and will cause smoking and leaking rivets.
Using a cleco in every hole install the parts, then wipe out any sealant in the dimple prior to installing and shooting the rivets. Do not use rivet tape and pre-load the rivets in the holes since there may be some squeeze out into the dimples of adjacent holes as you rivet the parts together. Starting at the forward most hole, remove a cleco and shoot the rivets one at a time working forward to aft, repeat untill the rib or stiffener is complete. Wipe the squeeze out off of the skin and tools with acetone or MEK as you go and before the sealant cures.
After you get the stiffeners and interior ribs installed you can install the outboard close out ribs using the same technique. Apply a generous fillet seal to the skin to close out rib seams and wait a few days for it to cure prior to instaiing the aft tank wall. It is not necessary, but if you want to back seal the rivet tails now is the time to do it. I reccomend buying a pint of A2 sealant for this application. I prefer to overcoat the rivet row as opposed to dome sealing individual fasteners since there is more surface adhesion area and less chance of the sealant seperating. Keep in mind that you must ensure that there are zero voids around the rivet tails, or else you are not accomplishing anything. A paint brush with the bristles cut off short works well for applying the A sealant. A circular application motion around the rivet tails will help you obtain proper adhesion and minimize voids, you can then smooth out the sealant in a back and forth motion.
Install the rear tank wall using a slightly heavier than normal application of sealant. In this application I reccomend an even coat of sealant on the skin flange as well as the rear wall flange since some of the sealant will be displaced during installation of the part. Install clecos in every hole to draw up the parts and squeeze out the excess sealant. Duckbill pliers wrapped with masking tape can also be used to help draw up the parts and push out any voids in the sealant. Working from the middle outboard, remove the clecos and squeeze the rivets in the flange one at a time. Install the blind rivets wet with sealant, wipe off the excess and admire you're work.
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Don't overthink it....
I got analysis paralysis at the same point as you...don't over think it though. My brother and I did the following:
Stiffeners prosealed and riveted on day 1.
Proseal and cleco (every hole) all the ribs into the tank, and then rivet all of it, on day 2.
Rear baffle done day 3 (which was actually several weeks later).
Granted I had my brother helping me, but doing all the ribs in one day was not a big deal. We cleco'd every hole in every rib, then riveted. We used an awl to push the rivet into the dimpled hole when needed, wiped the squeeze out with a 2x2 paper towel, then shot the rivet. The bucking bar moved a lot on that wet proseal, so each rivet got a quick burst to fatten it up a tad, followed by a final shot to correct size. That was just the process we used that worked...trying to buck the rivet in one shot just was not working for us.
At no point did I feel the proseal was getting too thick / dry to work with. It took us at least 8 hours to do the ribs, and after we finished it was still plenty gooey.
We used a ziploc bag with the corner cut off and dispensed the proseal similar to dispensing cake decoration. We used a nice sized bead and I was real happy to see it squeezing out the dimples and the edges of each rib.
We cut at least 100 2x2 paper towel sheets to use to wipe stuff off (great idea, thanks VAF).
I got analysis paralysis at the same point as you...don't over think it though. My brother and I did the following:
Stiffeners prosealed and riveted on day 1.
Proseal and cleco (every hole) all the ribs into the tank, and then rivet all of it, on day 2.
Rear baffle done day 3 (which was actually several weeks later).
Granted I had my brother helping me, but doing all the ribs in one day was not a big deal. We cleco'd every hole in every rib, then riveted. We used an awl to push the rivet into the dimpled hole when needed, wiped the squeeze out with a 2x2 paper towel, then shot the rivet. The bucking bar moved a lot on that wet proseal, so each rivet got a quick burst to fatten it up a tad, followed by a final shot to correct size. That was just the process we used that worked...trying to buck the rivet in one shot just was not working for us.
At no point did I feel the proseal was getting too thick / dry to work with. It took us at least 8 hours to do the ribs, and after we finished it was still plenty gooey.
We used a ziploc bag with the corner cut off and dispensed the proseal similar to dispensing cake decoration. We used a nice sized bead and I was real happy to see it squeezing out the dimples and the edges of each rib.
We cut at least 100 2x2 paper towel sheets to use to wipe stuff off (great idea, thanks VAF).
I follow fairly closely, the process Mike has described with one exception...
Since the skins and ribs are designed for a net fit to each other (no specific expected gap caused by sealant is designed in), I begin riveting at the fwd most hole in each rib, and work towards the rear without skipping any holes. This helps the skin wrap around the radius of the rib (primarily the top side of the skin) and lay down as tight as possible to the rib.
But as long as you have good for/aft hole alignment along the full length of the rib, it probably doesn't matter.
Scott, I dug deep and stirred up my only two brain cells trying to remember exactly what order I shot the rivets, after a while it came back to me. When I built my outboard leading edges I clecoed every other hole and started by riveting the forward most three holes on the top side followed by the foward most two on the bottom side to get the skins to draw tight around the leading edge, then I riveted every other hole. This worked out OK but I did have to drill out a few rivets and reposition the rib flanges due to slight rivet hole alignment, especially toward the front upper flange of each rib.
When I built my tanks, as well as helping Jon build his -10 tanks, we clecoed every hole then shot the the top foward most three and bottom forward most two rivets to get the skin to draw up tightly, the we continued to rivet toward the rear without skipping any holes. Clecoing every hole and riveting without skipping every other hole seemed to help, but it could have also been that I was more proficient and had a better idea of how to position the ribs and skins. There is some practice required to cleco the parts together and obtain a really good hole alignment. Anyways I concur that clecoing every hole then riveting consecutively from front to back is probably the best technique to use. I will edit my previous post to reflect this.
