Fabricating trailer and frame?

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Fabricating trailer and frame?

Postby AaronRCTID » Tue Jun 24, 2014 3:56 pm

Hey there. Planning for our first build and the guy who is going to help out with welding and fabricating the trailer suggested we go ahead and fabricate a metal frame as well. Anyone have any experience with this? Wondering what pros and cons of this would be instead of traditional method of plywood and slats as the 'frame' of the build. Thanks!
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Re: Fabricating trailer and frame?

Postby Dale M. » Tue Jun 24, 2014 9:21 pm

Problem with metal frame for cabin is once its set, its awful hard to change design on the fly... Oh it can be done, but modifications come at higher cost (time/effort)...

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Re: Fabricating trailer and frame?

Postby KCStudly » Tue Jun 24, 2014 9:44 pm

You also need to be more careful about thermal bridging, where hot and cold are conducted easily thru the metal skipping past any insulation. Alaska Teardrops has the materials and techniques down pat, using VHB tape and rivets to attach skins, and plastic corner trim. He has some very lightweight construction, as well. IMO anybody considering building the cabin frame in metal should read his stuff.

http://www.tnttt.com/viewtopic.php?f=27&t=51991
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Re: Fabricating trailer and frame?

Postby ctstaas » Fri Jun 27, 2014 8:12 pm

You sir, are correct. I made my frame out of steel square tubing and my cabin from marine grade plywood separately, and then assembled them together near the end of the build. My frame turned out perfectly but the plywood was 1/16" out of square from the mill and I didn't check until it bit me. By the time i finished that 1/16" turned into a 1/8" fix.
My point is,it's a camp trailer and the only thing that needs to be perfect is the towability and safety. Have fun making it suit you and your needs.
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Re: Fabricating trailer and frame?

Postby Ropes4u » Fri Jun 27, 2014 8:16 pm

My axle arrived Friday and I hope we have a rolling trailer this weekend. I will build the shell and attach it to the trailer with bolts.
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Re: Fabricating trailer and frame?

Postby AaronRCTID » Mon Sep 07, 2015 11:55 am

Thanks for the feedback, especially the link to the folks in Alaska, @KCStudly. Still weighing this out. I'm leaning toward not framing the entire thing in steel, but maybe having a steel beam or two, bridged by a cross-beam at the roof, where I can bolt on the doors and roof. I need to read more up on all that thermal stuff. I want this thing to be fairly comfy and functional all year up here in the Pacific Northwest. Excited to start the build this spring! Cheers
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Re: Fabricating trailer and frame?

Postby Prototear » Wed Sep 09, 2015 1:38 am

I am currently building a trailer with 1" steel frame walls like you are considering and using some of the methods learned from Alaska Teardrop's builds. I got my frame from Oregon and dragged it home and did some significant modifications to it but kept the basic shape. I like having the steel framed walls because it leaves me the option to (eventually) use it as either a camper or a cargo trailer since it doesn't need the lateral structure of the galley wall to keep the sides from flexing. I plan to make my galley cabinets removable to enable this. I have a 1x2" steel tube between the walls where the galley hinge will go and this (with a few others) make this super stiff.

To reduce the thermal connection through the wall frames, I used VHB tape for the skin (but mainly did it for the clean look) and I plan to attach the interior 1/4" plywood skin with plastic fasteners like that used in car interior panels of some kind (still need to pick out one that looks decent and is removable for maintenance).

This frame has a few more steel members than it really needs, partly because of my mods and partly because it was partly over-designed at the start. If I could have designed it from the start there would be less steel in it and I'd change the contour to be more like a Benroy in the rear to get my galley countertop closer to the rear opening and have portion of the top flat to make it easier to fit the fan and sunroof.

The first entry in my build journal shows how the sides were formed and held for assembly by the original frame builder.

Are you considering welding the frame yourself? Just curious....
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Re: Fabricating trailer and frame?

Postby AaronRCTID » Thu Sep 17, 2015 4:57 pm

Hey there, thanks for chiming in! I'll start my build thread soon so I can post my design. To save weight and hassle, I'm not going to bend any metal. Instead, I'll have 3 vertical posts that wrap across the roof. My plan is to sandwich in the posts with 1/2"-3/4"ply on the exterior, foam insulation, and luan interior. I'm going to do the same and make my galley cabinets (well, any cabinets and shelving) removable to be installed after the walls are in up. I'm going to do an aluminum roof.

I'm curious what you mean about the VHB tape for the skin? I thought VHB was pretty thin and used to join the skin to the frame, not as the skin itself.

My dad and his buddy are doing all welding/fabricating, that's the only part I'm not doing myself.
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Re: Fabricating trailer and frame?

Postby Prototear » Thu Sep 17, 2015 10:50 pm

AaronRCTID wrote:I'm curious what you mean about the VHB tape for the skin? I thought VHB was pretty thin and used to join the skin to the frame, not as the skin itself.


The skin on my trailer is aluminum and I could have been clearer with: I used VHB tape for [attaching] the skin.

Yes the VHB tape is fairly thin with a foam core in it. It serves as a minor thermal break between the thermally conductive materials of steel and aluminum, but it is only a minor thermal break providing a tiny bit of insulation rather than a conductive path.

Even though you are not curving any of the steel frame members, will you put any straight across the tops of the vertical pieces between the left and right sides? If so it can help stiffen it up and you might be able to get by with thinner plywood on the sides and the overall structure wouldn't be as dependent on the strength of the side plywood.
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Re: Fabricating trailer and frame?

Postby AaronRCTID » Wed Sep 23, 2015 12:45 pm

[/quote]
The skin on my trailer is aluminum and I could have been clearer with: I used VHB tape for [attaching] the skin.

Yes the VHB tape is fairly thin with a foam core in it. It serves as a minor thermal break between the thermally conductive materials of steel and aluminum, but it is only a minor thermal break providing a tiny bit of insulation rather than a conductive path.

Even though you are not curving any of the steel frame members, will you put any straight across the tops of the vertical pieces between the left and right sides? If so it can help stiffen it up and you might be able to get by with thinner plywood on the sides and the overall structure wouldn't be as dependent on the strength of the side plywood.[/quote]

I appreciate that explanation, I haven't quite got a handle how and why VHB tape is used. (I don't quite understand those thermal dynamics of a build yet.)

That's exactly the plan, I'll have at least 3 cross beams joining the walls for strength and to hopefully cut down on wood weight. I'm planning to have the walls made of luan, light insulation, and lighter ply on the outside.
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Re: Fabricating trailer and frame?

Postby dales133 » Wed Sep 23, 2015 1:04 pm

I just used some of that vhb tape to stick composite panel onto a steel frame and I was suitably impressed.
The thermal barrier mentioned if done correctly stops moisture transfer from outside in and also stops corrosion from unlike metals contacting g each other
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Re: Fabricating trailer and frame?

Postby KCStudly » Wed Sep 23, 2015 3:09 pm

A little primer on heat transfer: The way I understand it, heat travels thru metal relatively easy compared to wood, and especially easy thru aluminum. If you were to rivet aluminum skin directly to a steel cage there will be a slight resistance to transfer due to the little air gaps and discontinuity between the surfaces, but wherever there is intimate contact, such as where the rivets clamp well, the heat will still travel toward cold. In cold weather the aluminum skin acts like a big radiator, pulling heat out and dissipating it. Now the VHB tape is thin; but it has a thin foam core that allows it to conform to larger and opposing surfaces better (relatively speaking... in other words, the thickness and compliance of the foam core allows the very thin adhesive tape portion on either side to do its job even if the two matting surfaces are imprecise); and it is far less thermally conductive than metal. So by placing the VHB tape between the steel and aluminum you form a thermal break. In addition, you also get a structural bond that greatly reduces the number of rivets needed, and therefore the number of additional thermal bridges, further reducing overall heat transfer. Even a very small thermal break can make a big difference, so the thickness (or thinness) of the tape is not trivial.
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Re: Fabricating trailer and frame?

Postby AaronRCTID » Sun Sep 27, 2015 11:47 am

Ah thanks, that makes sense. So do folks usually use VHB tape between aluminum and wood as well? Eg, aluminum roof to the wood walls?
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Re: Fabricating trailer and frame?

Postby Shadow Catcher » Sun Sep 27, 2015 1:16 pm

One thing to be mindful of is axle placement for correct balance, ours is too far back and my tongue weight is too great ( I am afraid to get the actual weight :roll: )
There is a formula on the site some place.
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Re: Fabricating trailer and frame?

Postby Redneck Teepee » Sun Sep 27, 2015 2:53 pm

Shadow Catcher wrote:One thing to be mindful of is axle placement for correct balance, ours is too far back and my tongue weight is too great ( I am afraid to get the actual weight :roll: )
There is a formula on the site some place.

If you are building some type of specific trailer with contents/holding tanks etc. that will have a higher than average load fore or aft of the axle, then you will have to have all of that info, placement areas and weights for planning the axle placement.

On another note, if it is just an average teardrop with the normal sleeping/galley areas 60% of the trailer floor area (not counting the tongue/forget the tongue) should be in front of the axle center line. Its also important when building to triangulate your coupler center line off the axle centers at the spindles (assuming the axle has been squared with the frame) so it will pull true and straight. :thumbsup:
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