recommendation for skinning a steel frame?

Jfet

Adventurer
I wanted to pop over to the experts on here to get ideas on how to skin a steel frame since it might be something you find on expedition trailers.

This is actually going on a flatbed truck, but the process should be the same.

I want to build the frame out of 1x1, 1x2, 0.065 and 0.120 steel tube. I have done a drawing of a possible frame design and the weight is fine (580 pounds). I think welded steel will be better than aluminum for cost, durability, and I can weld steel easier.

Now to the problem. I construct a steel frame, how do I skin it such that I can get a smooth side, waterproof, for a reasonable cost? I had thought about using 3M tape or Sikaflex252 to bond some sort of FRP to the steel, but if I paint the steel first to prevent it from rusting, isn't this going to provide a poor surface for the tape or glue? If I don't paint the steel, that seems bad too. If I rivet aluminum siding to the steel, I have to worry about galvanic corrosiion, plus leaks at the rivets.

Any suggestions? For reference, here is a picture of my envisioned steel frame (thanks in advance for any ideas!):

steelframe.jpg
 

Cody1771

Explorer
not an expert on this but sikilflexing aluminum plate might work, or you could use 1/4 ply or door skin with self tapping screws (counter sunk so the head doesn't poke out) then Fiberglass over?
 

AZ69EB

New member
Why not steel on steel? You can weld 16 gauge down to 24 gauge mild steel over your frame and just paint it. A little heavy, but strong.
 

mmuthart

Observer
This just shows my aluminum diamond plated laid out so I could first drill the several dozens of small holes....but I first powdered coated my frame, then pop riveted the aluminum diamond plate using stainless steel rivets. I dipped each rivet in a 3M Autobody Sealant to hopefully keep the elements out. It turned out very nice.
 

Attachments

  • P1000253_2.jpg
    P1000253_2.jpg
    196.5 KB · Views: 45

Haf-E

Expedition Leader
Check out this link - Rob Gray's Australian camper "Wothahellizat" -

http://www.robgray.com/graynomad/index.php

He used aluminum plate - on the first build he attached it with 3M VHB tape and then for the second build he went with Sikaflex.

I think if you went with the aluminum plate you could space the "studs" farther apart - and perhaps do some triangulation of the structure instead of the original "stick frame" type design. If you infill the spaces with foam insulation the resulting structure gets really strong. So the aluminum skin becomes structural that way.
 

mhiscox

Expedition Leader
Camper Mog had an aluminum skin riveted to the steel skeleton. It was waterproof because of angled pieces at all the corners, also riveted, but goobered up with Sikaflex or similar underneath. Never leaked a drop.

Camper Mog 012.jpg
 

Haf-E

Expedition Leader
Here is a picture of what I meant by triangulation...

Rob Gray wothahellizat frame.jpg

Sorry the image is so small.
 

Jfet

Adventurer
Cool, thanks for the info and links, especially to the RobGray build.

We were going with stick frame to make skinning easier (standard bonding surface) and it also makes cutting the foam pretty standard. We can add some triangulation though if it feels wobbly.

I am sort of sold on the aluminum skin with sikaflex 252 bonding the aluminum to the steel. I was thinking about doing full height 16 inch wide panels of 0.090 5052 aluminum. If I make them butt joints, I could replace a panel if it were damaged. There may be two problems with butt joints vs overlap.

1) There will only be 1/2 inch wide area of sikaflex 252 on the narrow studs for each aluminum plate edge. This may be ok.

2) Thermal expansion. Aluminum expands 2x the rate of steel...about 1mm per meter IIRC. Does this mean my butt joints would look like crap when I travel from the NW down to the SW? If I painted the aluminum, would the paint crack at the joints.

If I overlap join the plates, like most box vans and rental trucks, I think the look would be better and the glue would have as much surface area as you desire, but removing a panel without destroying the neighboring panels becomes impossible.
 

Jfet

Adventurer
Verkstad I think you are correct, however the very impressive Wothahellizat mk 1 and mk2 both had butt joints on the rather thick diamond stud aluminum plate. You would think that if he had had thermal expansion issues on mk1 he would have done something different on mk2.

Or maybe it is just always hot as #@#$ in Australia and it was always expanded :)
 

uriedog

metal melter
What about building the frame from 4130 aircraft chromoly. Strength to weight ratio is far better then mild steel, and costs less then aluminium.The majority could be built from .035 and .049 wall tube.

Welded with ER70S-2 .035 rod makes for very strong joints with plenty of flex.
 

Haf-E

Expedition Leader
I think rob gray's truck didn't see much cold weather- so i doubt expansion/contraction occurred. I also think the "five bar" pattern on it hid any ripples (but keeping them lined up to match adjacent panels was a major hassle he said).

I would go for more triangulations for strength and accept the hassle of making insulation fit.

I know a fab shop in BC that usually.stocks the european 5 bar plate in 5x16 sheets if your interested. I've bought 2 sheets from them and had them shear them to the size I needed.
 

Jfet

Adventurer
hmmmm, for a newbie welder, I am unsure about chromoly...

I would rather have smooth sides than the diamond plate. I am thinking overlap is the way to go, as that will allow for some expansion (the sikaflex has some stretch and the panels can slide on top of each other a bit. Just hope if one gets damaged it is the first one...
 

Forum statistics

Threads
185,541
Messages
2,875,678
Members
224,922
Latest member
Randy Towles
Top