Teardrop Newb doing a 7 day build

[tubularfab]

Ok, I've been lurking for about a year since deciding I needed to build a wide teardrop for traveling with my young boys. I'm a mechanical engineer / welder / fabricator with 3 boys - aged 5, 8, and 10. I own a mandrel tube bending shop with lots of fab equipment and have access to things like wood shops, waterjets and laser cutters at work. However, access to all those resources has been a hindrance! I've drawn and designed trailer after trailer with every cool feature I could think of. What I needed to do was build something!

So, I like to go to antique engine shows, and am leaving for one Friday morning with my oldest son. I figured this past weekend was a good time to jump in and give building one a go! I am making a box that will sit on a polar bear 4' x 8' utility trailer that I've had for at least 10 years. Simple, cheap, and lightweight are the design goals, and I plan to tow it with a '98 Mercedes turbodiesel. I went wide - 6' - so it can fit the boys and I, with a 48" maximum inside height. I started with a floor platform - framed with 2x3's and decked with 1/2" plywood.

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Then I built a frame out of 1/2" emt welded together.

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[tubularfab]

The frame is covered with 5/32" luan from Home Depot. It seems plenty strong after bonding and screwing together. I used a 24" radius for the curve, which I achieved by bending the emt over a flywheel for one of my antique engines. The flywheel was about 36" diameter, which was almost perfect as the spring back in the tube made it relax at 24" radius. This radius was definitely tight for the luan - I would not want to go any tighter. I soaked the luan with a spray bottle of water, and then used heavy ratchet straps to form it around the trailer frame. I left it sit overnight and dry before releasing the straps and screwing it into place.

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[tubularfab]

I'm using flange head self drilling screws to pull the skin into place. I'm also using liquid nails heavy duty construction adhesive to attach the skin since it is supposed to grip the galvanized metal really well. I have never used it before, but it seems to work well. After the glue fully cures I am going to pull the flange head screws out and replace them with something countersunk.

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The real trick was trying to do this with 2 panels side by side. Keeping the width to 48" would have been much simpler. The luan did not want to bend in the other direction, so splicing was my only option.

[tubularfab]

I had an old Mallard 5th wheel trailer from the 1980's that I bought and planned to renovate several years ago, but it turned out to be in worse shape than I realized. So, this spring I demolished it to save the frame, and also kept some of the windows and hatch doors. There was a hatch door that I though would make a good main door. Obviously I need to come up with a more normal latch.

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There was a 35" x 36" sliding window that seemed to want to be on the opposite side on the trailer:

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Both are just barely stuck in place to check fit - they will have to come back out soon enough to finish other areas. I need to clean those parts up, too!

So, that's where the trailer is right now after a couple of sessions of work (maybe 8 hours total?). I'm quite pleased at how fast it's coming together! I need to build a panel to close in the back end, but want to make it removable for an important reason - to get the mattress in when I'm done! I have a spare queen sixe mattress that's like new, and need to be able to slide it in. I was originally going to hinge the frame to the deck so it could hinge up, but I think the rear access panel is going to be easier to seal up. I do plan on adding a galley to the back down the road, but want to make it a separate enclosure because I think it will be easier to keep water, etc from leaking into the living space. I do not have time to do the galley right now.

I have also debated at length on how to cover/seal the wood. I think I am going to try the PlasTex panels at Home Depot, which are .060" thick textured plastic panels in 4' x 8' size. I'm going to attach it with contact cement, and use the plastic connector channels HD also sells join them with some kind of sealant in the channels. I'll then cover the corners with aluminum angles, and hope shrinking the one edge will allow it to conform to the curve.

I'm not worrying about insulation right now, but will be adding it later. At that time In can also find some 1/8" luan and finish it out nicer. On the other hand I might just start over with a better idea of what I want!

[AmericanMade]

I love the fact you are using EMT. . . .Totally cheap and light and strong when constructed right.. . .

RL

[dogscats]

Great looking build .I try to weld some EMT with a 220v mig . flux core .35 . It look bad .How did you do it?

[tubularfab]

I'm not a huge fan of welding emt together, but as I mentioned before this the alpha/prototype tear to get me started. I do plan to build a much nicer one with better lines and more features down the road...

As far as welding emt... I spent 6 years teaching welding and fabrication at a technical college, and still train students on how to weld but on a not for credit basis. There are some tricks for the emt, as there are 2 major problems with welding it. First, the stuff is really thin - probably pretty close to the thickness of the wire in your MIG welder. Second it's galvanized, which is great for corrosion resistance but terrible for welding. Heating or welding on something that has been galvanized will release very toxic zinc fumes into the air, and you must be careful not to breathe it. If you do you will be instantly rewarded with flu like symptoms - it's nasty stuff. Anyway, the most important trick that helps with both these issues is throw proper welding techniques to the wind. Set your welder up as if you were going to weld something much heavier - shoot for a very hot, crisp arc on clean steel. I believe I was set for about 19.5 volts and close to 400ipm running .030" wire. If you were to make a proper, continuous weld at these settings you would quickly vaporize the emt tube! But, instead of holding the trigger nonstop across the weld you want to pulse the trigger on/off very quickly (I call this technique "triggering"). The idea is that you use the extra hot arc to burn off the coating, but stop the arc before it nukes the tube. A split second to cool before the next spot weld, and everything (hopefully) holds its shape. I will take a pic of the resulting weld next time I am by the shop. It's not pretty, but you can get good welds this way.

Another trick I used to simplify the welding was to flatten the end of the tube a bit at the joint. I did not take time to cope any of these joints like you'd want to if you were building a race car chassis. All the tubes were simply cut square using a tubing cutter. I tacked the joints were the two tubes touched, and then smacked the ends of the tubes with a dull chisel to flatten the side wall in closer to the other tube. Makes welding easier due to less gaps and a straighter weld path. Makes the joint lose a little stiffness in the plane you flatten to - but it's a good trade-off for the ease it provides to the welding.

I've actually never tried to use a flux core wire feed welder on emt, so I cannot say for sure that this will work as well with that type of set-up. I think it should - but make sure you don't let it cool so much between triggerings that the flux hardens - might make restarting the arc tricky.

[dogscats]

Thanks. will give a try.

[tubularfab]

Ok, made more progress. Got all of the luan on, primed the deck top and bottom, set the mattress in, and put the shell on. Oh, also covered the shell with the PlasTex material from Home Depot. I used 3M 77 contact cement to attach it, and will be covering all the seams with one sided butyl tape from Home Depot. The tape is the very sticky black stuff - I will then screw white pvc corner and flat molding on over top of it. The biggest frustration today was poor quality sheet metal screws. I picked up 2 boxes of the same exact brand and size - one at Lowes and one at Home Depot. The box from Lowes worked fine, and they all pulled down nice and tight. The ones from HD would not tighten; as soon as the taper under the head hit the luan they spun free. Pulled them back out, and all the threads were flat - looks like they forgot to harden them. When soft EMT is harder than a sheet metal screw you might have a problem!

I know the mattress is ridiculously thick for this, but it's one I already had that was very nice and barely used. So, free wins for now!

Here it is now - got a few more things to do in the morning before it hits the road!

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[greygoos]

I like your build. It is simple and looks cost effective. Am looking forward to seeing the molding on.

[daveesl77]

A problem I see is the Plastex on the exterior. The thing is, it is not made for exterior use and will expand and contract up to 1/4" in all directions. I have it on my interior top/front/rear surfaces and considered doing it as a roof covering until I saw the warnings from both the mfg and those that used it previously. Sunlight can seriously degrade the product.

dave

[tubularfab]

Ok, the trip is over and I haven't even posted a "complete" pic yet. By complete I mean the state it was in when I started the trip; it is still a long way from complete. Here is how it looked when I got to the campground after 220 miles of interstate including 20 miles through an extremely intense thunderstorm complete with torrential rain:

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But I should revert back to the building first. Before applying the molding I ran 2" strips of one-sided butyl tape over all the corners and seams. I got the tape at Home Depot - it was a huge 6" wide roll, which was way wider than I was looking for. I hacked off part of the roll on the band saw, but the cut was not very nice. You can see the black butyl peeking out from behind the molding in the pics. My plan was to trim it off with a utility knife, but I didn't have time before starting the trip, and it really bonded well during the trip (saw up to 101 degrees F on the car's display while sitting in traffic) - now it doesn't want to peel off! I spent a lot of time debating over what to use for molding on the exterior. I am definitely pro-metal, but due to a severe lack of time and not having easy access to a sheet metal shrinker I decided to go with the PVC molding from Home Depot. The stuff was pretty cheap, and after making relief cuts in the lower flange every 2" it followed the curve of the roof really well. Flat strips did a good job of covering the flat seams. I attached it all with stainless sheet metal screws - which were just as poor quality as the zinc ones I mentioned before. 1/2" EMT should not be harder than a screw - but the threads were going completely flat on these screws. I was still putting the molding on about 2 hours after my planned departure time, and so the last bits are really rough.

And now I should talk about the Plastex - I really liked it before it left the shop. I still like certain things about it - it has a nice, clean look, it follows the curved contour with no complaint, it is super easy to trim with a utility knife. But it is not a material I'd recommend. As Dave mentioned, the thermal expansion is a big issue. I had not found reviews by anyone who'd used it as a skin, merely people asking about using it. I guess I should have researched it deeper. As soon as I pulled it out into the full 95 degree day from my 80 degree shop it started bulging. The contact cement could not hold it, and most of that blistered apart. It is now very lumpy - which is pretty annoying to me. But, it held it's watertightness through highway speeds in torrential rain. I later camped in it one night during rain and there were no leaks... So, I guess I have to call it a success, though it's not ideal and I will not use it again.

You can see the lumps/wrinkles here. This photo is after about 500 miles of interstate travel:

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It generated some conversation on the trip. Within 5 minutes of pulling in at the campground a couple of registered Tearjerkers had come by to check it out. At a gas station on the way a woman that had never heard of a teardrop before spent 5 minutes asking about it and where to buy one.

The project was a success, even with the Plastex issue. I needed to prove out to myself the idea of travelling with a teardrop. Part of this was seeing how the old Mercedes turbodiesel liked being a tow vehicle. It actually pulled very well, and has plenty of power to keep up with traffic. It's heavy enough to feel confident towing, too. I now have a test tear to figure out exactly how much space I need. And, I'm already designing revision B in my head...

[greygoos]

Great and fast build. Congratulations on your maiden voyage. Thanks for the heads up on the Plastex. I was contemplating using it over foam before covering it with canvas. I am a big fan of foamies for the simplicity but would prefer a smoother finish. Good luck with your future builds.

[daveesl77]

The biggest problem with the plastex is that it will break down with UV, which is why the manufacturer has the warning labels not to use it in an exterior location. I also thought it could be great for exterior use, but then found some videos showing how quickly it can degenerate. I don't think putting poly or another UV coating over it will work, as 1) it may not stick and 2) the expansion/contraction of the plastex would probably knock it off. I would seriously consider removing it, before it decides to remove itself while going down the road.

And like I said before, I like this stuff, used it inside mine. But it has it's limitations and they are severe.

dave

[Vedette]

Now that you have built a quick, easy, cheap sleeper teardrop trailer that your boys can sleep in, you can plan your second one for you and the wife.
With your shop and skills, we expect nothing short of "Aircraft Quality".
Shoot for the sky! Take your time! And knock our socks off!
Good Luck with your next build using your new found Teardrop building and using knowledge.
Good Roads
Brian & Sandi