Is an aluminium chassis a smart choice?

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Re: Is an aluminium chassis a smart choice?

Postby kennyrayandersen » Fri May 05, 2023 1:10 pm

Shadow Catcher wrote:Compass Rose is now 12 years old, the frame is all aluminum, unfortunately they did not use heavy enough aluminum for the tongue. The first one they built (and we owned) failed at the point where it goes under the body fortunately the second owner was going slowly and had it repaired. I had ours reinforced but was still concerned with too much flexing. During rebuild we moved the axel forward and again reinforced the tongue and no more flex.

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The problem isn't the material, or even likely the thickness of the material, but the design (since a number of miles got put on the frame in the first place). There are welds right smack dab in the middle of the highest stress area of the tongue. So, you introduce both a stress concentration (where cracks like to start) and you lose most of the heat-treat of the aluminum in the weld heat affected zone. I would let the tongue pass under the first cross member and attach it with an angle which that had two fasteners in the frame and two in the tongue, but all of them going through the center of the respective beams. That way you don't lose the heat-treat, and you don't have a fastener going through a high stress area. Do that and the frame, if sized properly, will never have a fatigue failure. I think even better is to combine the frame and tongue into an A-frame, which potentially solves both of those problems.
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Re: Is an aluminium chassis a smart choice?

Postby ABQ » Fri May 26, 2023 11:26 am

Hello KennyRayAndersen, Thank You for the great information & insights, especially highlighting germane equations & principles. Best Regards, ABQ :)
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Re: Is an aluminium chassis a smart choice?

Postby kennyrayandersen » Sat May 27, 2023 9:37 am

ABQ wrote:Hello KennyRayAndersen, Thank You for the great information & insights, especially highlighting germane equations & principles. Best Regards, ABQ :)



I hope my input isn't too much. I'm sure on one hand it might sound like I'm a know-it-all, but structural analysis is what I do for a day job and I've been doing it for nearly 40 years. I'm a little slow, but you're bound to learn a thing or two swinging at it for 40 years! I'm hoping to dispel a few myths, had help people make there trailers safer, stronger and lighter -- all of which can be done simultaneously if it's done right. It's been my pleasure to work with some smart people and I've have the opportunity to work with aluminum, composites, and steel. And now I'm working on an airplane which is wood as the primary structure!

In the end the right material is the right material. And each design should take advantage of each material, the design goals, and cost. Everything in the end is a collection of compromises that satisfy the problem your are trying to solve. Aluminum cost is higher, so in my opinion it should be used when saving weight is a priority in the design. Steel is cheaper, and compared to the aluminum available to the home builder, stronger, but the aluminum will be lighter for the same strength. The issue with aluminum is designing for fatigue considerations as well as making sure any welds are in low stress areas. By following good design practices there is no reason an aluminum trailer should last a lifetime!
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Re: Is an aluminium chassis a smart choice?

Postby tony.latham » Sat May 27, 2023 11:45 am

The issue with aluminum is designing for fatigue considerations as well as making sure any welds are in low stress areas. By following good design practices there is no reason an aluminum trailer should last a lifetime!


Any shade-tree welder can design and weld a steel trailer with a bit of help from a mentor. But that same guy can't design or weld an aluminum trailer that will last.

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That's the problem with the concept of a DIY aluminum trailer chassis--as I see it. :frightened:

Tony
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Re: Is an aluminium chassis a smart choice?

Postby kennyrayandersen » Mon May 29, 2023 8:23 am

tony.latham wrote:
The issue with aluminum is designing for fatigue considerations as well as making sure any welds are in low stress areas. By following good design practices there is no reason an aluminum trailer should last a lifetime!


Any shade-tree welder can design and weld a steel trailer with a bit of help from a mentor. But that same guy can't design or weld an aluminum trailer that will last.

Image

That's the problem with the concept of a DIY aluminum trailer chassis--as I see it. :frightened:

Tony


I'm trying to help that guy up his game. I wouldn't presume anyone incapable of learning something new -- it'd be like calling them stupid or something...

I also won't accuse anyone of being myopic... That's what these forums are for -- post some ideas, and get help from people that have the knowledge and the experience to help those with a little less 'training'. It's not that complicated - if you want to make a trailer chassis out of aluminum:

1) Don't put holes in the top or bottom of your aluminum members (put them in the middle of the beam)
2) Don't weld in high stress areas i.e. where the tongue meets the cabin (or anywhere near it)
3) You can weld in areas near the coupler, or near the axle attach where the bending is low (see this thread https://www.tnttt.com/viewtopic.php?f=35&t=75602)

It's entirely possible to make an inadequate steel trailer...
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