Teardrops n Tiny Travel Trailers

Hey folks,

Wanted to consult the pros, before I go spend silly amounts of cash on materials that may or may not be appropriate...

I'm not a carpenter; though I'm pretty good with steel I've seen the steel framed trailers done, usually using 1" square tube (.100 wall I assume?) My metal shop recently dropped off a catalog - and I notice they list 1 1/2" square ERW - down to as thin as .035 / 20ga.

Same shop has piles of scratch & dent alucobond - lots of4x8x3mm white sheets with a dented corner or two

Basically I'm asking if you folks see a problem with the material choice - plan would be to run 1 1/2" of insulation in the frame void; using the lucabond (likely riveted on) to face the inner and outer...

Would have to sit down and add it up - but at .69lbs/ft for the 20ga 1.5" tube, and .92lb/sqft for the lucabond, this seemingly could be a good way to keep the weight down... Or am I missing the boat?

Thanks in advance,

Andy

well, the only good point I see is that you can build a fire under it to heat it in the winter..

0.69lb/ft is the same weight as nominal 2x2 (actual 1-1/2"x1-1/2") wood, so they're not "feather light", though I don't doubt they're strong enough. One thing you might consider is running saw down the middle to make 1-1/2"x 5/8" channels - they would probably be all you need to support the skins at intermediate points.

Each skin of 3mm aluminium weighs the same as 1/2" ply, so that's not a lightweight solution.

I don't know if the direct thermal contact though the tubes means you will get hot/cold spots that cause a problem. My guess is that they wouldn't be a practical problem - unless you pressed bare flesh against them.....

Andrew

Ok, what am I missing? Construction has taught me to estimate plywood weight at 20-25lbs per 1/4" thickness (4x8 sheets). Not seeing how 29lbs of lucabond weighs more than 40lbs of plywood (?) Now given that lucabond is a finished product - and wouldn't require gallons of paint / finish...

Not seeing the thermal transfer issue though, I'm reasonably sure that composite core in the panels should eliminate that issue...Though I might have to put some more thought into thermal expansion issues...

AndyL,

I completely follow you on the Alucobond. One of the products that I have looked at is 3mm Polymetal. The Polymetal has aluminum skins that are a thinner gage (.013"-.015") than the .020" skins of the Alucobond, but the construction is basically the same, a 4x8 panel of Polymetal is about 22#. If you could get Alucobond at a deal, it sounds great. Some weight could be saved if you relied on the Alucaobond for a stiff, durable, prefinished external skin, and used lighter sheet aluminum (or 1/8" plywood) for your inner skin where the stiffness might not be necessary. But even if you used the Alucobond on the interior, it's not that much weight. The stiff composite panels would not need to have wall "studs" spaced as closely as a less rigid panel and that could save some weight. Without doing the math, I would guess that you could do an Alucobond/steel tube/Alucobond stucture with insulation for about the same weight as 3/4" plywood.

It sounds like you are more comfortable working with steel than wood, which is probably opposite of most of the folks on the forum. With a steel body framework you could weld all of your joints then skin the framework. That's been done, you are just looking at a different type of skin that is much more rigid than what they have used and shouldn't "oil can" on you. Oh, and it's prefinished if you can keep from scratching it up during construction. Leave the protective film on until last.

Are you thinking about a traditional teardrop shape with a curved side profile? If so then you will have to consider how you would bend portions of the steel tubing. Others on the forum have done this. But if you were thinking about bending large section, thin-walled tube you might run into problems with it kinking. If it were me, and I wanted to use steel as a framework - just opinion - I'd look at 1" square, maybe 18 gage so that I had a little thicker wall material. That should be plenty rigid for what you are trying to do, unless this will be a really large trailer.

I've played with the Polymetal material and there is very little insulation effect with it. Heat will transmit through the material pretty well, it does not act as much of a thermal break. This would have to be considered in your design. Using a bonding tape to attach the outer skin to the steel framework will allow for thermal expansion differences between steel and aluminum and would act somewhat as a thermal break. It's used often for high-end trailers without additional mechanical fasteners. See:

http://multimedia.mmm.com/mws/mediawebserver.dyn?6666660Zjcf6lVs6EVs66Ser3COrrrrQ-

There are generic bonding tapes that don't cost what 3M's products do and probably work nearly as well.

I'd encourage you to keep looking at your design. There was a recent thread that looked at some of these possibilities, as well as others, that might be of interest to you if you missed it.

http://www.tnttt.com/viewtopic.php?t=23005

J.B.

I had read that thread, and it was partly why I was thinking about the alucobond.

I'm not too concerned about insulation - worst case - it's not hard to polyurethane the tubes if required. But I don't believe the alucobond skin is going to transfer heat quite the way sheet aluminum will. Cold spots due to colder steel on one side shouldn't transfer to other quite so readily given the composite core.

Planning to use one larger radius bend - ~8' radius don't forsee that bend as a big headache...

I'm not sold on double sided sticky tape - I'll consider it though

AndyL, it sounds like I've got it wrong - I was assuming you were talking about finished aluminium sheet, but it sounds like Alucobond is something different (it isn't a trade name I've heard over here in Britain).

Andrew

You're right about the heat transfer with the composite, it wouldn't be nearly as bad as straight aluminum. If you PM me with your address I could send you a small sample of some of the tape to play with. I agree that if you were going to bend the composite over an eight foot radius you'd want to at least tie down the ends of the sheet with mechanical fasteners.