Hey Guys,

Nothing real exciting here. Just a trailer hitch for an Audi TT. It's for a friend's father.

Here's the catch, he wants it made of aluminum. I'm pretty much limited to 1/4" trickness because of my machine.

Do you guys think this design would hold up for pulling an ATV or Jetski ? The end plates bolt to the frame rails of the car, and the tubing is 2 x 2 x 1/4" square tubing, except for the receiver tube which is 1.75 x 1.75 x 1/4" ...

 

I wouldn't touch aluminum for a hitch receiver, not worth the risk

 

i would also maybe add another set of gussets on the end plates on the side that would be towards the back of the car to aid in the pulling force from the trailer. but other than that, looks good and should be strong enough for light use. maybe heat treat it if you can.

 

Why out of aluminum ?
If he is wanting to use aluminum for weight than that is one thing but if he is trying to avoid having it rust then could you use stainless instead ?
Iam sure it would still be strong enough in Aluminum though.

 

Unlike steel, aluminum doesn't have an infinite fatigue life. Any aluminum structure that is subject to cyclical loading (like your tow hitch), regardless of the amplitude of the stress, will fail at some point.

For the most part, your design will be fine for a reasonable number of cycles. The only design flaw is how the main bar (2x2x0.25") is attached to the end plates. The way you have it, the welds around those two seams are in shear. The maximum stress occurs at those two places and they will be the first place where failure would occure. My suggestion is to cut a 2x2 square in the side plates and insert the main bar in and then weld on each side. You wouldn't need any additional gusseting beyond what you have in the first picture.

I'm just being curious, why must this be aluminum? You could make it out of steel and powder coat it. It'll be cheaper.

 

Build out of steel, get it powder coated silver.

 

No way in hell I'd be making that from aluminum, if I had too I would be adding more gussets to the end plates that mount to your chassis, and to the cross bar as well.

One thing I like to do for gussets on square tube framework is use angle instead of flat bar, its a lot stronger.

 

I would use 4x2 rectangular tubing in place of the 2x2, and larger gussets as mentioned. (4" side being in plane with the pulling load)
It will be fine. The fatigue life of this will be outside of the use by a large margin.
The only reason I would do it is because it's a car, so you know the guy won't get stupid and try to pull something big. Add in he likely won't be overly brave as to where it goes terrain-wise, and it's not a big deal.

 

Sorry for the late reply.

He wanted aluminum because he wants it to be as light as possible, and because he doesn't tow anything heavy with it. He says max 1000 lbs. The part that worries be the most is the receiver tube being made of 1/4" thick aluminum.

Here's an updated version :

 

It's not worth the risk man. Tell him you refuse to make it out of aluminum, simple as that.

Is he willing to spend the money on real testing to find out what it will take to make it safe out of aluminum?

Sometimes you've gotta know when to turn the business away.

 

I wouldn't risk making something like that out of aluminum. What happens if it fails and a 1000lb trailer goes off the road and kills a family of 5.

 

A steel version really won't be all THAT heavy.

 

He is dead set on aluminum.

Thanks for your input guys!

 

Hmmm...maybe he doesn't get it.

 

If he's dead set on aluminum tell him you're dead set on not killing someone.

If someone brings me an idea like this and INSISTS it be built a certain way or out of a certain material he better have professional engineer listed on his business card.

 

If you decide to do it anyways, make it out of 7075 and have it heat treated after so it doesn't fail right away.

 

yeah because 7075 is a prime choice for arc welding

 

There are a ton of trailers made out of aluminum. This is not suicide guys.
If you want, make little "washers" around the holes on the receiver out of 1/4", so it will be 1/2" thick there. Also, change that little brace on top to a piece of 4x2x1/4 hss cut at the right angle, and welded all the way across. cleaner, stronger, and less work. (wish I could throw up a sketch, hope you know what I mean)
As long as he knows the cost of doing this in aluminum, go for it. I have done so much with aluminum, it has not proven disastrous as many think.
Just my .02

 

Who said anything about arc welding

 

make 3 of them, have the other 2 load tested, all on his dime. factor in a saftey margin of like 3x the load requirement. remember to cycle test it also. keep copies, and disclose to him the results and only rate it for a certain speed on the road and a certain weight. etch this rating into the bar then as well.

i think youd be ok then. just thinking about liability from a legal standpoint should it fail and someone get hurt.

 

this sounds like a mission man.. im sure you dont want any of the liability when it fails... simply tell him that you wont do it unless its out of stainless.

failure on the highway = lawsuit = agtronic down the tubes.

 

he needs to get a truck, never got the trailer hitch on a "sports" car. It’s like saying "I have this fancy car and these cool toys to pull around, but I’m still the retard that has to bother my friends, any time I need a sheet of plywood from the home depot” utterly useless

 

Dave i meant arc welding as a blanket term , anyone here have access to FAE software like Abaqus?

 

I know, I am just making jokes the last few days, obviously not my skill set, back to work...

 

i knew you were joking but instead of made me question what you were thinking. lol