Ultralight chassis - build with tubular aluminium

[legojenn]

http://www.angib.pwp.blueyonder.co.uk/t ... tear57.htm

I was planning to have this frame custom-built for a trailer build that I want to start next spring. The builder suggested that for safety, I use tubular aluminium for the build. The tubular metal would be stronger and the aluminium would be lighter.

Considering the size of the trailer, the extra cost would not be that significant. Is it worth it? I would rather have something a little stronger and safer and unpainted aluminium looks prettier than painted steel.

Feedback would be much appreciated. I can't wait to get started on this project.

Strange, I get a spelling error in Firefox if I use the North American spelling of Aluminum.

[eamarquardt]

Tubing is far stronger than angle for the same weight.

I've seen a few pictures on the internet of welded aluminum frames breaking. I think Shadow Catcher had a failure of the welded aluminum frame of his first MegaMini.

Steel is a lot more forgiving of poor welding technique. I kinda think, to get the same margin for error, you'll have to use bigger aluminum than is optimum to keep the stress on the welds acceptable.

I'd do the calculations and see exactly how much weight you'll save with an aluminum frame. Balance that with cost as fabricating out of aluminum will be considerably more expensive than steel.

I think if I had my heart set on aluminum, I'd bolt it together with well designed joints rather than weld it up. A friend has a really beautiful boat trailer made out of aluminum and it is all bolted together.

Just my thoughts w/o any factual back-up.

Cheers,

Gus

[legojenn]

Thanks....before I posted, I should have read what was already written. It seems that there are at least three recent threads discussing aluminium v. steel with steel winning. Steel it is.

[Lgboro]

Probably the greatest deterrent to building and aluminum frame (cost aside) is finding a welder that is really skilled and competent in welding aluminum. I still am leaning aluminum as I have a neighbor who is very skilled working with aluminum and stainless and has almost exclusively works in these two metals and consistently is sought out by companies in a large area to do specialty welding for them. I hope to built #2 smaller than my current 4 x 9 and sub 500 lbs. so every lb. will count if I am to be successful in building a tear at this weight.

[pete42]

I worked in an iron and aluminum foundry for 41 years they welded aluminum everyday using TIG and MIG welders.

I have a friend who makes midget race cars using aluminum tubing he also is one of the best welders around.

my brother who also was a welder on gas pipelines for many many years before becoming the guy who certified other welders.

what I'm getting at is the aluminum welds are as strong as the steel ones both need to be done correctly

if the aluminum race cars hold up I would not be afraid to use aluminum in any trailer

In fact the cargo trailer I am thinking of buying has an all aluminum frame and tongue

I say go for the aluminum if that's what you want.

I have seen pictures of a steel "A" frame shaped tongue breaking where it was welded to the frame of a travel trailer.
the site I saw it on was trailer lifes site couple three years ago.

pete

[angib]

Yes, using tubes instead of angles will be stronger, weight for weight. That is what I've done for the Pico-Light chassis and using that design would be better.

An aluminium chassis, if it is much lighter than a steel chassis, will eventually crack (at a weld). That might take 50 years, so that would be fine, but it might take just 5 years.

[oicu812]

The biggest problem with welding Alum in the home shop or small shop is annealing it to get your strength back. You lose up to 80 % of your strength depending on the alloy. With a small frame like you want you could do it with a temp stick or crayon and a torch, sounds like your welder is capable talk it over with him. You might want to think about 4130 chrome molly, certain amount of cool factor,very strong and light, easy to weld, rust resistant. A little expensive but the amount you need wouldn't matter. just my 2 cents.

[Bogo]

The biggest problem with welding Alum in the home shop or small shop is annealing it to get your strength back. You lose up to 80 % of your strength depending on the alloy. With a small frame like you want you could do it with a temp stick or crayon and a torch, sounds like your welder is capable talk it over with him.

How about avoiding welds... Bolt, or rivet, and glue the joints. Make a fittings for the corners, then glue and bolt or rivet the long pieces to it. For the tongue, put it under the frame so there are no weld joints at the front of the frame. Use brackets to bolt or rivet the tongue to the frame at that point.

[angib]

How about avoiding welds... Bolt, or rivet, and glue the joints.

You could use the same technique that works fine on the 'racks' of top-end sailing dinghies. Fit the aluminium tubes together closely and then wrap the joints with carbon biaxial cloth in epoxy resin. You could use glass cloth but it would need to be thicker - and wouldn't look so cool.....

[Bogo]

A good page on the heat treatment of aluminum. It tells the basics of why it is needed and how it works.

http://www.mlevel3.com/BCIT/heat%20treat.htm