Tank vs Standard dimple dies

While in the process of preparing the tanks for sealing I have had time to research the best application of tank sealant and lessons learned from other builders along the way. I wanted to have the best product that I can build and so I decided to make up a couple of samples using both standard "spring back dimple dies" and tank dies. I learned that tank dies make the hole .005" deeper to accomidate the sealant under the rivet head. The first sample was two sheets of .025 using standard dies. I wanted to try the fay sealing method that has been discussed about here at length. I was able to get the flange to set flush and create fillets and fully encapsulate the shop head of the rivets. I made two more samples using .032 skin side and .025 flange side, one with tank dies, and one with standard dies. After fay sealing and letting tack up for a day or so, I wet installed the rivets and set them with a squeezer.

When I was finished I found that setting the rivets with the tank dies was slightly more cumbersome and hard to get the rivet to stay in one position while being set. It seemed to wallow around a bit and the shop head was hard to set without cleeting over slightly. I assume that the sealant acted as a bit of a lubricant. The skin side had a noticable recessed area or dimple around the manufactured head of the rivet. Several of the rivets stuck up at an angle. Not bad but noticable. The rivets set using the standard dies were less difficult to work with and seemed to lay down better with no noticable dimple or recess. I can only assume that the rivets set using the tank dies had more sealant under their head as opposed to the ones using the standard dies.

I plan on fully encapsulating the shop head of the rivets so as to preclude leaks at that point. My final conclusion was that I plan on going ahead with standard spring back dimple dies for all 3/32 rivets. Here are some pictures.


First sample.


Tank dies. Notice the dimples or recessed area around the rivet head

Standard dies. The rivet head lays flat in the dimple

I suppose that using either standard or tank dimple dies will produce a good leak free product, but I tend to like the appearance using standard dies.

Thanks!

Thanks for doing this and taking the time to post it. I will remember this for my next project.

Many, many RVs were built before the invention of the "tank dies". Frankly, we never saw the need for them.

Great study

Thanks for both experimenting with this and especially for sharing your results. I appreciate the spirit of questioning our assumptions as we build. Is there a chance the squeezing procedure or tool that was being used when the tank dies were invented is somehow different than what you used here? I guess I'm wondering if someone went to the trouble of machining a specialty tool to solve a problem they thought existed, maybe it really did exist, but maybe with the squeezer you're using or something else about your process, you've "solved" whatever problem the inventor thought they were seeing. (Or perhaps it all was just another case of a solution in search of a non-existent problem.)

--Stephen

Good results can be achieved with either type of die, but I got nice results with the Cleaveland tank dies. Here are my thoughts from about a dozen years ago:

http://thervjournal.com/tankdies.html

Just to be sure; you used standard dies on the skin and used tank dies on the rib, correct? The tank dies are designed to allow the sealant between the skin and the rib, not really "under the head". You don't want to use the tank dies on the skin.

I used the tank dies on almost all the under-structure and achieved very good results. The idea is that two pieces dimpled using the same die won't fully nest into each other.

Dave

As Mell said...

Mel said:

Many, many RVs were built before the invention of the "tank dies". Frankly, we never saw the need for them.

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One thing I recently learned from a guy who used to work for Boeing regarding pro-seal. He said that after you set the rivets do NOT wipe the wet proseal off with MEK or anything other chemical. Just let it harden.

The theory is that the MEK will push into the proseal by the rivet head and cause micro leaks. He went on to say that MIGHT be the reason for the paint blisters some builders are experiencing.

I have no idea if this is true but it is an interesting theory and may explain why some people are having problems while others are not.

Nice work Mark....and a good decision. Oversize dimples are wrong as a soup sandwich.

Just to be sure; you used standard dies on the skin and used tank dies on the rib, correct? The tank dies are designed to allow the sealant between the skin and the rib, not really "under the head". You don't want to use the tank dies on the skin.

Click to expand...

I've been out of town and haven't had time to respond to the thread.

Dave, I used the tank dies on one sample and standard dies on the other sample.

I Spoke with the designer of my tank dies and he explained the history of the tank dies and how they came about. He said that they dimple .005" deeper than standard dies to allow space for the tank sealant to to set between the skin dimple and the manufactured head of the rivet so the rivet head wouldn't set proud of the skin. He said originally the old timers would take a debur tool and run it around inside the skin dimple several tmes to make up for this. Then someone got the idea to make a special deeper 3/32 die to do this for them......thus the tank dies. I may be missing something here but I don't think the tank dies are designed to allow for the sealant between the skin and rib.

My samples proved to me anyway that using tank dies would produce a rivet that sets slightly below the skin surface. A problem? No, but cosmetically I didn't like it. The best dies that I have found are the spring back dimple dies that Avery sells. http://www.averytools.com/prodinfo.asp?number=3/32 DDS.
They have spring back angles on both dies that make a superior dimple.

I plan on encapsulating the shop head of each rivet to preclude a leak path around the rivets. We'll see how it works out. One thing my pop taught me "don't buy cheap or it'll look cheap".

I think the question was, did you use the tank die on both sheets? Or, did you use the tank die on the underlying sheet, and standard die on the top sheet, where the rivet mfg head will go?

I thought the correct usage of tank dies was to only use them on the underlying surface. Then use standard die on the top surface.

PCHunt said:

I think the question was, did you use the tank die on both sheets? Or, did you use the tank die on the underlying sheet, and standard die on the top sheet, where the rivet mfg head will go?

I thought the correct usage of tank dies was to only use them on the underlying surface. Then use standard die on the top surface.

Click to expand...

As I understand the concept, the tank dies create a dimple about 0.007" deeper than standard to allow for that much proseal between the sheet and the underside of the rivet head, so you'd want to at least use them on the top sheet. Up until now, I've always used my tank dies on the ribs too, to get the skin dimple to nest better; there's proseal in that joint too. Even on joints without sealant, using the tank dies on the substructure helps the skin nest better. I'm thinking about getting "substructure" dies for tank stubstructure, which make dimples about 0.011 deeper than standard dies (0.004 deeper than tank dies) to allow for better nesting AND a little room for proseal.

N941WR said:

......One thing I recently learned from a guy who used to work for Boeing regarding pro-seal. He said that after you set the rivets do NOT wipe the wet proseal off with MEK or anything other chemical. Just let it harden....I have no idea if this is true.....

Click to expand...

I don't know what production line your guy worked on but as a guy who also used to work for Boeing with 30+ years working with proseal on a daily basis, I can assure you that wet, excess sealant is very quickly removed from the airframe using MEK or other suitable solvent. If that guy let the proseal harden, I can well imagine the next shift personnel who had to clean it up would have something to say about that.