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Author Topic: A recipe for disaster  (Read 2390 times)
Tikvah
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« on: June 05, 2011, 02:47:16 PM »

Im preparing to skin the side of my coach within the next week or two.
I will be welding in some structural steel for the new windows and some support to span the large window areas that will be blanked out.
I got to thinking.  Im going to rivet aluminum over steel.  Wont I get some kind of fast deterioration from the incompatibility of the two metals?
How do I protect the aluminum?
What kind of rivets do I use?
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« Reply #1 on: June 05, 2011, 03:14:48 PM »

I don't have them but I KNOW you really do need answers.  I say this only to encourage you to keep looking.

Why are you using aluminum?  Weight, rust, principle, need to heat the skin while fixing it in place, desperate for a complicating factor, what?  The rest of the structure is mild steel and it doesn't rust unless provoked and left naked.  Stainless steel would be way more expensive if that is the drift.

Buried in this hilarious post is some really good information. Huh Shocked

John 
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« Reply #2 on: June 05, 2011, 03:39:55 PM »

The answer is no Eagle and other have done it for years you won't like the aluminum if you have long or big sections it will wave like Old Glory in the sun

good luck
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« Reply #3 on: June 05, 2011, 03:49:25 PM »

Unless you already have the aluminum...use 18 ga steel, much easier to use and finish.   Smiley Smiley Smiley Smiley
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Tikvah
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« Reply #4 on: June 05, 2011, 06:10:26 PM »

My mistake.  I thought aluminum was the product of choice.  I've studied this forum to death, and it just seemed that aluminum was the common answer.  I've heard of using other products, but aluminum seems the standard.

18 gauge steel?

I have almost 25' to skin on each side.  I can only buy in 12' sections.  So, I plan to do two big parts and one smaller section in the rear.

I'm open to correction NOW.. before I make the investment.
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I couldn't repair my brakes, so I made my horn louder.
1989 MCI-102 A3
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Started in Cheboygan, Michigan (near the Mackinaw Bridge).  Now home is anywhere we park
robertglines1
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« Reply #5 on: June 05, 2011, 06:19:37 PM »

I have better luck with 16 ga cold roll   less waving than the 18ga  cold roll seams to hold paint better (I learned that back in my hot rod building days) no scientific reason ;it just has been so for me. I make my laps to match original skin laps on coach at old window post (every 2nd or 3rd one)  Do you have mig gun? Going all way to roof gutter?   Bob
« Last Edit: June 05, 2011, 06:29:44 PM by robertglines1 » Logged

Bob@Judy  98 XLE prevost with 3 slides --Home done---last one! SW INdiana
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« Reply #6 on: June 05, 2011, 06:49:57 PM »

Dave, Are you located just across the bridge in the UP?   I didn't chime in on the steel vs alum before because I thought you had made up your mind. I have always used steel and fastened by mig welding from the inside. If you get set up rite you won't be able to see where it is attached: spot about every 3 inches. if you dimple or pimple either fill or grind smooth. I tuck up under gutter on top. I tried 18 on present project and ended up taking it off and putting 16 back on. lesson learned. I have skinned 4 coaches with steel. It is extra weight. but is minimal is the grand sceam of things.   Bob
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Bob@Judy  98 XLE prevost with 3 slides --Home done---last one! SW INdiana
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« Reply #7 on: June 05, 2011, 08:19:13 PM »

always have 16 and 18 ga around. like the others said... 16 is best for sides... for making trunklids, etc for streetrods i use 18.
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RJ
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« Reply #8 on: June 05, 2011, 11:34:45 PM »

Clifford -

I'm a little confused - IIRC, that big old billboard area down both sides of Tikvah's MCI is aluminum sheeting.

If he uses the same or thicker gauge aluminum as the factory for covering some window areas, why wouldn't it work?  Especially if he's using short panels.

I understand the different heat absorption rates between steel and aluminum, thus the wavy sides, but am a little stumped otherwise.  And I'm not dissing the folk who use steel, just curious.

Please elaborate to educate!  TIA!


Tikvah -

In answer to your original question, MCI used this sticky black tape stuff between the steel and aluminum to thwart galvanic corrosion.

There's a part number floating around out there for the stuff, but it might be easier just to call MCI Service Parts.

Not sure about the rivets, sorry.

FWIW & HTH. . .

 Wink

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« Reply #9 on: June 06, 2011, 01:12:19 AM »

On my bus, they used 75 gauge aluminum over steel-but with a mylar layer in between to keep corrosion down to a minimum. Hence my 34 year old bus with a 11 year old paint job has only a couple of small bubble spots.  I believe they used aluminum rivets (maybe stainless-non magnetic).
On my truck conversion they used the normal 48" aluminum panels, but with 60 gauge (30 gauge is standard) using 3M two sided tape that insulates the two metals from each other.  Good Luck, TomC
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Tikvah
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« Reply #10 on: June 06, 2011, 03:00:56 AM »

Quote
Dave, Are you located just across the bridge in the UP?


I live just below the bridge, almost can see it out my window.

Let's go back to a couple things.
 - The aluminum is more likely to cause waves?  So, if I go with steel, I can use the 12' sheets (or more) without as much trouble?  That sounds convincing to me if it's true.  I've been very worried about how to get everything hot enough not to wrinkle.
 - Did I hear you right, I can tack weld the 16 ga sheet metal to the structure?  Does that mean I can skip the rivets?   I would love to tack weld this stuff.

More thoughts?

Just for information.. I removed both the top gutter and the center trim strip.  It was my intention to tuck the window skin behind both of these trim strips.  That way all the horizontal seams and fasteners are hidden.




« Last Edit: June 06, 2011, 03:59:42 AM by Tikvah » Logged

I couldn't repair my brakes, so I made my horn louder.
1989 MCI-102 A3
DD 6V92 Turbo, Alison
Tons of stuff to learn!
Started in Cheboygan, Michigan (near the Mackinaw Bridge).  Now home is anywhere we park
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« Reply #11 on: June 06, 2011, 04:51:51 AM »

Dave I stayed at Tiki on north side and met a guy named Dave that worked on Bridge. I welded sheets from inside and can't see where length would make differance with the welding and rivets would not be needed. I did use the stock trim piece between steel cover and rear cap joint --weld slow and make sure you spots aren't pulling sheet- like spot skip 12 inch spot  skip etc  then fill in gaps  spot skip etc: prob didn't need to tell you that just watch you first set of welds and alternate sides of tack no need for 3 inch pattern on each side of frame work  maybe .One mistake I made on first to avoid is make sure seal metal edges around edges where they will lap over bottom horrizontal seam to prevent rust streaks.Hint put silicon bead on and screw in place to hold (temp) before welding. Remove screws and fill holes.  I'm re building a factory Prevost Xle salvage shell (1200$) now I mentioned $ only to let you know I'm not high dollar! It has Alum on part or it from the factory!!. It waves in the sun!! I'm putting 3 slides in and using steel 16 ga and it stays smooth.  If it was not so much trouble at this point I would change it all.   Bottom seam of skinn needs to overlap sign board but do as you will with trim.  I will pm phone # if you want to talk.   Bob
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luvrbus
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« Reply #12 on: June 06, 2011, 05:23:59 AM »

RJ, I never owned a MCI that did not wave you know how us Eagle folks are no waves and steel is the way to prevent it.
The GM will wave on the smooth side also even with the 10,000 rivets on a 4905A lol the older 4104 and 4106 don't, the rib siding all the way to the top prevents that .
Believe it or fiberglass is by far the worst of any material for waving been there done that with R&M siding.
Like Robert I heated and stretched the steel and welded without the rivets look down the side of Matt's Eagle steel is the way to go

good luck
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JohnEd
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« Reply #13 on: June 06, 2011, 05:41:10 AM »

Tik,

I have read repeatedly that to use aluminum you MUST heat the alu with huge heaters and then with the sheet still hot you quick like a bunny rivet it in place starting at one end.  Once you get it riveted down hot and flat it won't go wavy in the sun until the sun heats it hotter that it was at the time of install.  Safari had God awful alu sides that were wavy as seen from a couple hundred yards distant.  They resolved this by using enormous banks of heat lamps fixed to a frame that were 40 feet long and 8 feet wide.  Suspended from an overhear winch affair.  The sheet goods were heated laying down.  Complicated process but they resolved the wavy side problem.

To get away with alu rivets you would need to use structural rivets and that involves hammering with rivet guns.  I think your only option with alu siding is to use high quality sealing stainless steel rivets.

I believe you can get steel siding in 40 ft lengths and in the exact width you need to do it in one seamless pass.

If you don't glue the edge that goes up under the roof you will have a air leak or permiation.  This might seem like picking fly crap from pepper but it isn't.  40 ft of that unglued seam might ad up to a 2 square inch hole in total.  Going down the road there is a powerful "suck" inside the coach and that 2 inch hole can admit a lot of hot/cold air (like this post) that your ac or heaters must deal with.  even parked with any wind you get a lot of ambient air to process.  With as much harping as we do about insulation a "hole in the wall" sets the teeth to grinding.

Good luck,


John

My post crossed with Clifford's.  Heating steel?  First I remember hearing that.  Clifford can not be argued with so get one of those diesel powered flame thrower heaters for the bus interior and install it in the summer sun.  Don't forget your salt tablets.
« Last Edit: June 06, 2011, 05:45:45 AM by JohnEd » Logged

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We can easily forgive a child who is afraid of the dark; the real tragedy of life is when men are afraid of the light.
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Jeremy
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« Reply #14 on: June 06, 2011, 05:46:40 AM »

The skins on my bus are galvanised steel, and they seem to be entirely glued on - no rivets and no welding. I'm surprised welding the skins is even an option as I'd have thought it would cause distortion of the thin metal.

Regarding the '...skins will wave even with 10,000 rivets' thing - my instinct would be that the more rivets you use the worse the waving will appear - you cannot stop the material expanding, so more rivets just creates more fixed points and thus more areas where the metal has to bow outwards in order to accommodate it's expansion. If the skin is attached using a flexible adhesive (eg a Sikaflex-type polyurethene product), the whole surface of the skin can expand and contract with minimal restriction, without the 'waves' forming.

That'd be my guess anyway

Jeremy

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« Reply #15 on: June 06, 2011, 06:03:52 AM »

Boomer used aluminum on his Eagle but it was one huge piece from top to bottom never knew where he found a piece that large but I notice he gets a few waves on a hot day he did the best job with aluminum I have seen.
Newell uses SS for their siding nice but a little pricey for the average person

good luck
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Tikvah
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« Reply #16 on: June 06, 2011, 06:09:40 AM »

Quote
I believe you can get steel siding in 40 ft lengths and in the exact width you need to do it in one seamless pass.

The longest I can find in my area is 12' length (40" width - up to 48")
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« Reply #17 on: June 06, 2011, 07:41:37 AM »

...  Im going to rivet aluminum over steel.  Wont I get some kind of fast deterioration from the incompatibility of the two metals?
How do I protect the aluminum? ...

Without weighing in on the aluminum-vs.-steel discussion, the deterioration you are talking about is called "galvanic corrosion" and, yes, it can be a real issue if any moisture comes in contact with the assembly.

FWIW, we re-skinned the roof on our otherwise steel bus with aluminum.  To avoid galvanic corrosion we used butyl tape between them and butyl-sealed "bulb"-type rivets.  Then we painted the roof.  In seven years we have not noticed any issues with galvanic corrosion in the roof area.

-Sean
http://OurOdyssey.BlogSpot.com
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« Reply #18 on: June 06, 2011, 07:53:31 AM »

I have heard aluminum wheels against steel wheels will cause galvanic corrosion any truth to that ? as I never saw it before

good luck
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« Reply #19 on: June 06, 2011, 08:06:18 AM »

I have heard aluminum wheels against steel wheels will cause galvanic corrosion any truth to that ? as I never saw it before

Yes, it will, especially in areas with lots of road salt as the resulting salty water makes a better electrolyte than fresh water.

Alcoa sells a dielectric disk to put between your aluminum and steel wheels, or between your aluminum wheel and steel drum, to minimize the effect.

-Sean
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