Campy McCampface has a problem...

[videographer]

Hi all, I've been gone a while.

Finished Campy up to about what I would consider 90% - sleepable, comfortable, air conditioning for the wife, Yeti electrical system with batteries and a (not yet functional) solar panel. Had a custom frame made out of 2" aluminum angle. Towed it down to Missouri for the solar eclipse in Sept 2017 (which we got clouded out of by 5 minutes!), towed it to central Wisconsin for the Energy Fair, a couple other small trips.

Before the beginning of the 2018 season, I pulled off the right wheel, doing some maintenance, only to find a vertical crack in the frame directly behind where the stub axle attaches. Couldn't quite understand what the stress could be to make that crack in that way, but whatever. Had the original welder have a look at it, lift the body off a few inches, and weld in a patch.

Guess what? Pulled the same wheel off in May - same crack, same place. See picture.

Not sure what I'm asking here...I've essentially decided to have a new frame made out of 2" steel tube, with exact bolt holes so I can pick up the cabin and drop it back on a new frame. Has anyone else seen this? The welding guy actually said to me that "aluminum frames are only really good for 6 years anyway." Really?

I guess it goes without saying that I'm pretty reluctant to drive it any distance.

[Socal Tom]

Hard to give any advice without understanding how weight is distributed, but my guess is that the frame is a bit under sized for the weight, and there is probably weight further out that is causing the stress to be created there.

[MtnDon]

The welder is making excuses with his comment about the longevity of aluminum frames. Peterbilt, etc have had aluminum frames, sometimes as an option, for decades. The biggest problem with them is from road salt corrosion.

I would not call that "weld-over" a patch. A patch, to me, means welding a plate over the cracked area.

For that to crack from the lower edge up there has to be a force acting to cause it. Hard to say what without more detailed pictures showing where the tongue etc is. The picture shown makes one think the tongue could be to the left and that the area between tongue and axle is causing a bending moment where the frame cracked. But as said, w/o better knowledge that is a guess. But I think it is safe to say the design was deficient.

You mentioned making a steel frame from 2" tubing. Do you mean square tubing? For a trailer frame, square tube is not as strong as a rectangular tube when the rectangular tube is positioned with the larger dimension vertically placed; like a 2x3 tube with the 3" vertical and the 2" horizontal. Is that explained clearly? Same as a wood 2x4 has greater bending resistance when on edge than when laid flat. Most often, for a trailer frame, the tubing should be rectangular. Often a 2x3 or 2x4 can use thinner walls and be stronger and lighter or the same weight as a square tube with thicker walls.

[tony.latham]

I’m with Don. A patch would have been done by adding another piece of aluminum over the welded up crack.

I would think the patch should be feet and not inches in length. On both sides.

Tony

[Philip]

Find a better welder. That isn't a weld. Its just a gob laid on top of a crack. The outside edges show no penetration. Heat to low. I bet the crack was not "V" out.

Looked like a spool gun weld. I would have used a tig. Weld the crack solid. Then plate over that with another section of the same angle.

[videographer]

Ooops, my bad. Tongue/front is to the right, rear is to the left. The crack is directly behind the plate that the stub axle assembly bolts to.



I did muse aloud if maybe sandwiching another layer of angle over the top and welding that up could be helpful (the displacement of the camper body would be negligible) but I was assured this would be enough. Rest assured that I *am* looking for another welder.

The weight on the frame is variable depending on where I put things inside the trailer (of course) but I would estimate 55% front/45% rear on average. In any event, I still can't quite grok why the crack would go *up* when the stress generally pushes *down.* Vibration?

[Socal Tom]

Either the stub axle
Mount ends about there, or the tail of the trailer “waves” up and down as you drive would be my guesses.


Sent from my iPhone using Tapatalk

[Zzyzx]

First, I am NOT an expert on these things. I have, however, done a fair bit of research on the internet, which should be taken with a large grain of salt.

Apparently, welding aluminum can cause it lose temper. Over time this leads to cracks.
Adding patches or bracing may increase the problem creating new cracks.

Finding a welder who has experience and understanding of aluminum construction is critical.

[Socal Tom]

From my experience this is true. It might work better to bolt a new section over the crack vs weld in a patch


Sent from my iPhone using Tapatalk

[KCStudly]

Another thing to consider is that if you just weld a rectangular patch, the edge of the patch becomes the new point of stress rise. Consider a diamond shaped patch with long tapered edges that land in the middle of the side rail. That way the stress concentrations run to the middle, or neutral point of the side rail when it flexes.

Yes, welding aluminum anneals it, so it will have a much lower yield strength after welding.

[GPW]

Question …. On breaks like this it would seem easiest to just bolt on more material to the frame than trying to weld it … But when adding more Aluminum ( bolted ) …. do we have to worry about dissimilar metals ? Steel bolts on an Aluminum frame .. ??? Just asking …

[MtnDon]

Moisture is needed to have any corrosion. Zinc plated steel is better than stainless steel, but electroplated zinc is very thin. The hot dipped galvanized steel bolts are better, maybe the best. S/S bolts, in the presence of moisture, actually promote the corrosion of the aluminum.

If the frame is a square tube one problem with bolting is how to prevent the tightened bolt from squashing the tube.

[Aguyfromohio]

...If the frame is a square tube one problem with bolting is how to prevent the tightened bolt from squashing the tube.

We had that issue mounting fender brackets to our frames.
We installed rivet nuts on just one tube wall.

[RecklessCreation]

a couple posts above I believe nailed it... the section behind the break is vibrating or 'wagging' and it's using the hard edge of the stub axle mount as a bending or sheer point. (actually very similar to how lift/lowering blocks on a leaf spring cause axle wrapping )

there are several ways you could accomplish stopping this .. but without seeing the base frame and how much room you have to play with it's hard to give a real solution. ... but as low as you can at the stub axle mount put a cross brace... then at 1/3 intervals of that cross brace, put braces up to the end corners of the trailer frame... sort of a semi triangulation, this SHOULD stop/minimalize any vibrating or wagging up/down and side/side

and as said above .. that repair is crap, all it did was create a weaker spot directly on the original break (different materials/alloys, and heat treatment) .. it should have ATLEAST been whats referred to as a fish plate over that spot (sorta like a rectangle with pointed long ends)

[Zzyzx]

Yes, steel bolts through aluminum can lead to corrosion. Paint can help, also non-conducting washers are sometimes used. The part of the bolt penetrating the aluminum can also be jacketed with an insulator.