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Old 09-19-2017, 12:54 PM   #1
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1995 30' Excella
Harper Woods , Michigan
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a wish from a guy who needs to seal the holey roof

Hello, I'm about to gather my supplies, tools, and my nerve to go up and do a re-seal & caulking of all the holes in the roof in a 94 Excella 30 that has been neglected for 4-5 years. I suppose that this maintenance will always be necessary, but it makes me wonder why Airstream hasn't developed a better manufacturing process.

When manufacturing the roof, instead of just sawing/routing holes in the sheet aluminum, why not have forming/press die that simultaneously cuts the hole and forms a lip on the ductile aluminum, say 3/8 high that would shed water away from the hole? A computerized rolling mill with a forming die or bit could manage that for any configuration vents, skylights, and fans.

Does that make sense to a manufacturing engineer?
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Old 09-19-2017, 01:42 PM   #2
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Hi

Simple answer: tooling cost. None of these trailer configurations run in "high volume". Each hole pattern is specific to a configuration. Drawing the aluminum to form a useful lip (without breaking) is not trivial so the tooling is not going to be "simple". Allowing for a draw in a "stretched" panel would be tricky. The press(s) and dies cost money to set up and money to convert between runs. Either you have a setup dedicated to each layout (and lots of presses) or you do the setup / teardown on a weekly basis. Lots of cost either way.

Not simple to make and when you start to look at tolerances ... that's just the start.

Bob
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Old 09-19-2017, 02:16 PM   #3
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Hi

Simple answer: tooling cost. None of these trailer configurations run in "high volume". Each hole pattern is specific to a configuration. Drawing the aluminum to form a useful lip (without breaking) is not trivial so the tooling is not going to be "simple". Allowing for a draw in a "stretched" panel would be tricky. The press(s) and dies cost money to set up and money to convert between runs. Either you have a setup dedicated to each layout (and lots of presses) or you do the setup / teardown on a weekly basis. Lots of cost either way.

Not simple to make and when you start to look at tolerances ... that's just the start.

Bob

Not to be argumentative, but I wonder if the reasons you gave are still limitations. A CNC wizard could do this, I think. From what I've seen in one-man to bigger woodworking/cabinet shops, CNC has totally altered the manufacturing of millwork and cabinets.
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Old 09-19-2017, 02:49 PM   #4
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Originally Posted by Bob Blarney View Post
Not to be argumentative, but I wonder if the reasons you gave are still limitations. A CNC wizard could do this, I think. From what I've seen in one-man to bigger woodworking/cabinet shops, CNC has totally altered the manufacturing of millwork and cabinets.
Hi

I do CNC work. This is a tool and die draw process rather than a machining process. I've tooled it and done it as well. They aren't the same sort of thing. Simply put: CNC just removes material. In this case you want to *move* it from one place to another.

Bob
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Old 09-19-2017, 04:05 PM   #5
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Hi

I do CNC work. This is a tool and die draw process rather than a machining process. I've tooled it and done it as well. They aren't the same sort of thing. Simply put: CNC just removes material. In this case you want to *move* it from one place to another.

Bob
Hmm, why not have bit that cuts an opening near to size, and then a second that does not cut, but rolls the edge in one or more passes. If the metal is soft and thin enough such as the sheet aluminum, wouldn't that be possible?
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Old 09-20-2017, 07:09 AM   #6
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Hmm, why not have bit that cuts an opening near to size, and then a second that does not cut, but rolls the edge in one or more passes. If the metal is soft and thin enough such as the sheet aluminum, wouldn't that be possible?
Hi

That's not a cut operation, that's a forming operation. You do it with a die rather than a cutter.

As the metal stretches, it hardens. That limits what you can do without heat treating the material. Hard material cracks easily. That's *not* what you would want on your edge. Once a crack starts, it propagates. The answer is to heat treat the material to relieve the stress from forming. That gets you into a whole other set of issues.

You can play with alloys to make them a little easier to bend and stretch. This may do things to the strength and corrosion resistance that you don't like. You then make the material thicker and heavier to compensate.

All of this costs money ....

Bob
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Old 09-20-2017, 02:06 PM   #7
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This is really interesting! Both questions and answers are excellent. Thanks Bob_Blarney and Uncle_Bob for this educational and thought provoking thread.

Carla
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Old 09-20-2017, 03:48 PM   #8
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Just the slightest lip would go a long way to help keep water out
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Old 09-20-2017, 05:56 PM   #9
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Well, if a CNC router couldn't do it, so what if Airstream had to make separate factory manufacturing station with a punch and die press? For the money that a new Airstream costs, I don't think it's too much to ask.
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Old 09-21-2017, 08:26 AM   #10
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Hi

Well ok, would you pay another $30,000 for an AS with lips on the roof plus a few other often suggested "invisible" upgrades? The one thing you can be sure of is that anything like this is *not* going to be free.

Right now, the process of doing the holes is post install. They line up because the are drilled after everything is riveted in place (not quite 100% but close). To do them pre-install, you need to do all the holes in the panel at one time. That means a punch and die setup for each panel. Each hole that goes through inside and outside walls gets a punch on each panel. The panels aren't dimensionally the same so it's a unique setup for each of them.

Tolerance is the next issue. If you watch, they drill the rivet holes in the sheets so they match up rather than pre-punch them all. Holding tight enough tolerances to get them to line up is not simple. Improving this sort of thing has been an issue in aircraft, automobiles, and RV's forever and ever. Getting everything to match up .... yikes ....

You then get into design hours to spec out all the tooling. Inspection hours to check the results. Shop hours to keep it all in tolerance. Warehousing to store all the unique tooling for the next few decades. It goes on and on ....

Is this the whole story? Of course not. Is this exactly how you would do it and all the issues? nope. There would be a cost and it would be significant.

So, how much more would you pay? You *are* the target audience. You understand the benefit of the lip. It's worth more to you than to anybody else since you understand it. What does that translate to in increased purchase price? It only gets done if people will pay for it.

Bob
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Old 09-21-2017, 08:38 AM   #11
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You are way over thinking this, a simple scab patch with a faying surface seal is more then adequate. No special tools needed other then a rivet gun, drill motor, and a small piece of aluminum. If you want to get fancy you could put on a flush patch with countersunk rivets.
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Old 09-21-2017, 09:26 AM   #12
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In the plastic RV world, some folks are starting to use the spray on bedliner that you use in pickup trucks to seal their roofs.

Has anyone ever done anything similar to that with an AS? That gives you a completely leak free roof, no need to caulk.
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Old 09-21-2017, 09:56 AM   #13
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I sprayed on a bedliner to my popup trailer roof. It did a great job but seams are an issue. Btw the popup roof is aluminum covered. Seams would be an issue. It will stress crack at all the seams. My popup did just that with the center line seam. It does not leak as it's a fancy f/s seam but it did have to caulk just in case. Personally it's cheaper and easier to just recaulk everything every couple of years.
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Old 09-21-2017, 12:41 PM   #14
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The children

What about the children? I had a bad polish job and my insurance company covered all the roof ,window and door re-seal . They are paying Airstream $780 to complete the repair. This keeps an employee for a extra week so he can feed his children. In the Midwest it is difficult to find a experienced Airstream mechanic. Cutting out their expertise by the parent company would be costly to the parent and harmful to it's dealerships.
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