Hybrid steel and aluminum chassis

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Hybrid steel and aluminum chassis

Postby Lile » Wed May 05, 2021 8:33 am

Let me know if this sounds like a good idea or if I've gone rubber-side-up and shiny-side-down. :?

So I've been warned off several times about making a DIY chassis out of aluminum. On this forum, people have stated that aluminum tongues tend to crack. A welder was just speaking to me the other day about watching an aluminum bar being TIG welded, and a crack forming right at the weld 6" behind the new weld area. Although there are aluminum trailers on the market, they are commercial products that have been through rigorous testing. Aluminum fails suddenly - unlike steel that fails slowly and usually bends before it breaks. I've seen steel farm equipment that was full of stress cracks that still held together. WWII airplanes made of steel would still fly with half a wing shot off. I'm confident I can build a steel trailer that won't quit.

On the other hand, there was also a statement here that "the material that holds up your rigid cab box can be anything stiffer than spaghetti noodles". An exaggeration of course, but the cab I'm building is a really sturdy box, built out of 2" foam/1/4" plywood SIPs. It needs to be strongly anchored to the trailer frame, and supported, but the thing it is supported by is under very little force.

Here's a plan for a hybrid steel/aluminum frame. The main parts of the frame - the tongue, the connection to the axle (I'm using a 1400 lb Flexride torison axle from Southwest Wheel Company) are all steel. Tongue is 3" wide by 2" deep 0.125" rectangular tubing. Main cross members are 2X2X0.125" steel tube. The main tongue goes underneath all the other framing so there is a big weld to make everything stiff and sturdy. 2X2 steel angle iron forms the diagonal struts. All of these sizes come from recommended designs seen on this forum.

But then the angle iron frame that holds up the cab is made of aluminum 2X2 angle. I'm not welding any of the aluminum - it is bolted together and bolted to the frame.

What about dissimilar metals? Stainless and aluminum don't get along at all. Aluminum and galvanized steel fasteners are OK, according to an article by Fastenal which I'll dig up again if anyone cares to read it. The steel frame will be painted before assembling it to the aluminum parts (maybe powder coated). Any fasteners connecting aluminum and steel will be galvanized fasteners on painted steel, with a nonconducting washer between the fastener and the aluminum and a layer of thin durable tape against the steel. This is, as I have read, sufficient to quit worrying about galvanic corrosion between aluminum and steel. My old trailer is built this way and has no problems after 5 years.

Why go to all this trouble? Light weight. I'm pulling this trailer with a seriously wimpy tow vehicle. My goal is to make a teardrop that weighs about 500 lbs. Calculations show the trailer frame coming in under 120 lbs, and the whole assembled trailer estimated at 565 lbs. Cab is already built, so some of this is no longer an estimate. Originally the all-steel frame I was considering, built all out of 2X2 tube steel, would have been 260 lbs by itself. I've shaved off 140 lbs by putting the steel where it needs to be for strength, and the aluminum where it just ties the trailer down to the frame.

Here are some plans:


Steel Plan
Image


Aluminum Plan:
Image


Overall plan with dimensions
Image
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Re: Hybrid steel and aluminum chassis

Postby John61CT » Wed May 05, 2021 9:39 am

Substituting aluminum for just the lightweight bits won't save much weight.

The metal can be strong enough, it's the welding that's the problem.

https://www.clcboats.com/shop/products/ ... 0-clc.html

http://tnttt.com/viewtopic.php?p=1276850#p1276850
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Re: Hybrid steel and aluminum chassis

Postby twisted lines » Wed May 05, 2021 10:32 am

I used a bit of both :shock:
Racking up; And Rapin foam
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Re: Hybrid steel and aluminum chassis

Postby drhill » Wed May 05, 2021 3:49 pm

Maybe you don't even need the aluminum frame if the cabin has enough strength. The 2x3 tongue with the 3" in the horizontal isn't gaining you anything. Might as well use the 2x2 through out.
If you have a look at the pico light that might give you some ideas for a super lite frame. Not sure if a link will work. If not, type pico light into the search bar.

http://tnttt.com/Design_Library/The%20Pico-Light.htm
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Re: Hybrid steel and aluminum chassis

Postby MickinOz » Wed May 05, 2021 8:13 pm

Looks like a WOFTAM to me.
You lose a little bit of weight, but, then you have to bolt it together, then you have two dissimilar metals presumably electrically connected, unless you test every single joint for conductivity.
You only have to get a bit of wet mud on a joint and there goes your electrical isolation.
Put that on a an icy road that has had salt on it, or run it through brackish water, etc.

I would settle on one or other of the two materials.
At the very least, if you do mix the metals the steel should be hot-dipped galvanised.
Last edited by MickinOz on Wed May 05, 2021 8:19 pm, edited 1 time in total.
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Re: Hybrid steel and aluminum chassis

Postby twisted lines » Wed May 05, 2021 8:18 pm

I am with all of the above :applause:
Racking up; And Rapin foam
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Re: Hybrid steel and aluminum chassis

Postby Lile » Sat May 08, 2021 4:43 pm

MickinOz wrote:Looks like a WOFTAM to me.
You lose a little bit of weight, but, then you have to bolt it together, then you have two dissimilar metals presumably electrically connected, unless you test every single joint for conductivity.
You only have to get a bit of wet mud on a joint and there goes your electrical isolation.
Put that on a an icy road that has had salt on it, or run it through brackish water, etc.

I would settle on one or other of the two materials.
At the very least, if you do mix the metals the steel should be hot-dipped galvanised.


I believe I have already addressed the dissimilar metals issue in my first post, but to repeat:

Galvanized fasteners
Non-conducting washers
Non-conducting tape and paint on the steel

This is a proven system that I have used before. Fastenal has a technical article endorsing it, and my previous trailer build used this idea. So, my friend, I must disagree. I am simply not going to worry about it. You can build yours out of steel, with my blessings.
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Re: Hybrid steel and aluminum chassis

Postby Lile » Sat May 08, 2021 5:16 pm

drhill wrote:Maybe you don't even need the aluminum frame if the cabin has enough strength. The 2x3 tongue with the 3" in the horizontal isn't gaining you anything. Might as well use the 2x2 through out.
If you have a look at the pico light that might give you some ideas for a super lite frame. Not sure if a link will work. If not, type pico light into the search bar.

http://tnttt.com/Design_Library/The%20Pico-Light.htm



Well! This is the first truly useful suggestion here! I wish I'd found the Pico-Light before I started my build, it's kinda what I wanted to make in the first place. My weight estimate is well above what the Pico-Light's, but my cab is a bit bigger. I'm estimating the Aframe itself, sans wheels and axle is about 24 lbs, with a flexride axle and wheels that should come in at about 120 lbs for the trailer,axles and wheels. The Pico-Lite uses two flexride half-axles - coming in at 99 lbs - I'm worried about getting all that lined up perfectly, had been planning on using a full flexride axle.

With just the triangular style Pico-Lite frame, I'm shaving 55 lbs (thats 10% of the weight of the whole trailer). This is moving in the right direction.
Last edited by Lile on Sat May 08, 2021 5:32 pm, edited 1 time in total.
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Re: Hybrid steel and aluminum chassis

Postby Lile » Sat May 08, 2021 5:18 pm

John61CT wrote:Substituting aluminum for just the lightweight bits won't save much weight.


It will save exactly 30 LBs, which is 5% of the current estimated weight of the whole trailer.

Shaving a little here and a little there is how you get to a light wieght.
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Re: Hybrid steel and aluminum chassis

Postby alaska teardrop » Sat May 08, 2021 6:14 pm

Hope that you might find the threads listed below helpful in your designing effort. :thumbsup:
Northern Lite Traveler design: viewtopic.php?f=27&t=51991
Minimalist torsion axle frame: viewtopic.php?f=35&t=12220
Alaska Teardrop photo gallery: http://tnttt.com/gallery/album.php?album_id=2014
Glampette photo gallery; gallery/album.php?album_id=2983&sk=t&sd=d&st=0
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