Metal Conduit frame for Foamie Construction

[Postal_Dave]

I built my last camper with a wood frame. It turned out much heavier than I would have liked it. Some times the wood would warp and crack. The knot holes in the wood caused problems. I was looking for a substitute to use instead of wood for the frame of my next camper's roof that would be straight, lightweight, strong, and cheap. At first I tried PVC pipe but that was way too flexible. Metal Conduit seemed like a good answer. A 10ft long, small diameter pipe costs less than a 2X4 and is lighter. Connectors are available for joining ends. I was thinking of cutting groves in the foam and then using Great Stuff the glue the foam to the pipe.

Has anybody tried this already? What would be the downside of using it? Is there a better alternative? What are your thoughts on this?

Thanks for your input guys.
Dave

[John61CT]

This is an engineering problem.

Optimizing for lowest cost at a reasonable weight, or lightest weight at a reasonable cost

will require much of an engineer's skillset.

Now, reasonably light, not too pricey maybe an amateur can muddle through.

But Safety must be top priority, and conduit is just not load bearing.

Imagine your foamie is a removable pod sitting on a trailer's floor.

The chassis / frame suspended on the axle while bouncing down the road has to withstand **much** more violent forces than any static weight just sitting there.

You can get away with different size steel profiles, but I imagine even the lightest would be say 1 1/2" x 1/8 angle iron?

[John61CT]

Note I am assuming you mean to be towed by a powered vehicle?

Bicycle trailers are a different category, slow speeds more forgiving, less likely to kill others on the road.

[Postal_Dave]

Angle Iron? I'm not talking about building the trailer out of conduit. I'm talking about supporting a foam roof.

[GPW]

I’d think the PVC used in larger sizes could be strong enough and flexible like the foam is ... Sounds like some testing needs to be done ...

[GTS225]

I've been mentally exploring building the entire camper "pod" from a conduit/foam construction medium, and suspect it could do the job.
I've already built a roof structure for a '23 T-bucket out of 1/2" conduit, and was mildly surprised how strong of a structure one can get with a welded cage frame.
I would not suggest using any of the connectors, as they are cast zamak, and don't have much strength. I got some steel tubing matching the i.d. of the conduit, reamed the zinc out of the inside of the conduit, and cleaned off the zinc from the outside at the butt weld, so that I could get a good weld. Using a heavier wall steel tubing for an internal butt connector, and welding to it was an excellent method of joining lengths of conduit.
It does take some finesse at low amps with a wire welder, but it did work out. Now, 3/4" has a thicker wall, so should be easier to weld, and the wall thicknesses increase as the diameter increases.
It's a bit more difficult when joining at angles, but it can be done. Fish-mouth the end of the tube, clean off the zinc coating from both areas, and carefully utilize multiple spot welds around the circumference.
There will be some discrepancies matching conduit dimensions and foam thicknesses, as 3/4" EMT has an external dimension right about 7/8", so 1" foam is a little thick, and 3/4" foam doesn't quite make it, as far as a finished appearance to your surface.
I have not compared dimensions of 1-1/4" EMT to 1-1/2" foam, so it might turn out that those would be compatible.
In any case, as John61 alluded to, don't use it as a structural material, as it's too weak for any real load. Build your trailer a touch heavy for safety's sake, then make your "pod" in the manner you're considering.
My thought were that an EMT/foam/PMF structure would work, and I suspect one could even build cabinet framework inside, as long as the weight placed in them was limited.

If you go that route, please keep us in the loop.

Roger

[Postal_Dave]

Thanks Roger. Those are some great tips. Welding would be better, stronger, and less expensive since you wouldn't have to pay for connectors. Thanks!

My original thought was building a rectangle roof frame with two more rods going from side to side to hold up the vent fan. Then tracing it out on a 1 & 1/2 inch thick piece of foam. Use a router to make a semi-circle trench in the foam that the pipe would lay in. Use Great Stuff to adhere the EMT to the foam and then canvas it to encase the whole thing.
I imagine that after all that, the roof would have enough structural stability that it wouldn't fall apart. It might bend, but I doubt it would fall apart.

[Pmullen503]

Incorporating even a slight curve to your roof profile will stiffen up the roof considerably without added weight. Two layers of 3/4" glued together can take a significant curve without letting.

[John61CT]

Sorry for the crossed wires.

OK, so why not plain foamie PMF? We're thinking to span's too great?

Unless we talking a roofrack load?

[GTS225]

My original thought was building a rectangle roof frame with two more rods going from side to side to hold up the vent fan. Then tracing it out on a 1 & 1/2 inch thick piece of foam. Use a router to make a semi-circle trench in the foam that the pipe would lay in. Use Great Stuff to adhere the EMT to the foam and then canvas it to encase the whole thing.
I imagine that after all that, the roof would have enough structural stability that it wouldn't fall apart. It might bend, but I doubt it would fall apart.

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I tend to agree with you. By themselves, they may not exhibit much in the way of strength or stability, but combined, just like fiberglassing, the sum ends up being quite strong and stable.
If you're doing just a flat roof, it's possible that the weight of the vent fan may make if flex vertically, but I don't think it would sustain any damage.
I agree with Pmullen about incorporating a slight curve to the roof profile. It wouldn't have to be front-to-back, but side-to-side would add some strength to the roof, and help with water runoff.
To clarify; are you thinking of this to attach to wood/foam sidewalls?

Roger

[Nodrog]

So, here's what I know....I have weighed a 1x2, softwood, at just about 4 oz/ft. By a table from Steel Tube Institute (really) 1/2 emt weighs 4.8 oz/ ft. A 1x2 is pretty strong, say on edge as opposed to flat. I would sure think about a few 1x2's rather than trying to work in the tubing, unless the folding design just won't let you easily use a few 1x2s....Think about using some flashing at edges and around windows like ghcoe...viewtopic.php?f=55&t=60303 . Later....Nodrog

[Postal_Dave]

Nodrog, Thanks for your input. I didn't know that the 1/2" EMT was heavier that 1X2s

For my first camper, I made 1 X 2's by cutting 2 X 4's on my table saw. I'd rip an inch off the side of the 2X4 and by the time I finished the cut, the wood had already warped. 1x2's that were pre-cut from the store were just as expensive as a whole 2X4. Plus knot holes in the wood and splitting wood when I screwed the pieces together made for a real pain. That's why I'm kicking around this idea. I wanted to to get opinions and see if anybody had tried this and get the pros and cons of doing it this way.

[Postal_Dave]

Roger, the roof I'm thinking of making will have be a flat roof like my first camper. It is a folding camper that I find impossible to explain so here is a link to the build. The major change with the new camper is that I'm designing the galley to be inside the camper, so the back end won't open.
http://www.tnttt.com/viewtopic.php?f=50&t=49781

[John61CT]

Aha **that** F`ing Beauty!

Thing is I'm questioning the need in the first place?

Why don't you think pure PMF alone won't be structural enough?

[GTS225]

AH-HA! I'll have to concede that curves, (and angles), especially compound curves, don't fit well with a folding idea. In your situation then, I'd stick with the flat roof.
It may all be a moot point, as there's no weight savings as per Nodrog's post. It remains though, that there would be an advantage in no warping in the structural materials, and no rot in the event of water intrusion. (Well, there would be rot, but quite long term as compared to wood.)
There may be an additional disadvantage in having to attach round tubing to a vertical wall, as you might have to add something to get that task done in a secure manner, unless the entire structure is a welded tube framework. (Mental note: this is a folder.)

Doggone it Nodrog! With your weight comparison posting, you shot down my thought processes! Here I was thinking that it would save some weight, make a longer lasting structure, and even automatically give rounded corners for aerodynamic savings, and you have to come along and blow me out of the water with facts.

Roger