Tongue weld strength

[jdaan]

Hello again,

It's my habit to dwell on everything that could go wrong with my trailer. Now that I'm nearly finished with it (five years later), I've managed to stop worrying about most of it. One nagging worry is the strength of the connection of the tongue to the trailer body. I used the tongue strength guidelines to decide the gauge and design, which I think is sufficient, but now I'm wondering about the strength of the welds holding the tongue to the body of the trailer. I'm including a few pictures. It's a basic a-frame with a good amount of overlap. The welds were done by two parties, both experienced commercial welders. I have faith in the quality of the welds. The question I have is...is there enough strength in the design and existing welds to hold it all together down the road? Should I have included gussets or reinforcement? I've put about 50 miles on it so far with no problems, cracks, etc. I'm flying a little blind with this aspect of the build, so any comments would be greatly appreciated.

Thanks,
Justin

[eamarquardt]

Your trailer looks relatively small and light. It looks just fine to me. The way the tongue bars are attached will keep the frame from "racking".

Don't worry and go for it.

Cheers,

Gu

[Shadow Catcher]

The strength largely depends of the quality of the welds, if they were done properly you are good to go. If however you want some back up then also use bolts, particularly in the ends mid way on the sides. they will, given proper tongue weight distribution be in tension where the ones in front will be in compression. These bolts can also be used to attach to body of the trailer to the frame. buy a good quality grade 8 and use washers.
I am always suspicious of weld quality unless I know the welder. A number of the MIG welds on CR popped during the accident, a clear case of lack of fusion. Greg will be re doing them with TIG welds (much better choice for aluminum). The advantage is that there were a whole lot of them so a couple failing was not a problem. I see that I have contradicted my self to some extent having additional reinforced weld using gussets... might be a good idea.

[Lancie49]

What Gus said.

If you really are concerned, p'raps weld triangle filler sections into the front corners where they meet the drawbar.
Easy and quick job and if it makes you feel more confident of strength, worth the time it takes.

I don't reckon it needs it considering the experience of the blokes who did the job, but hey, what's it gonna cost $ and time wise.

Zilch

[eamarquardt]

Re bolting through the frame. The real strength comes from the top an bottom of the tubing. When drilling through the tubing it is better to drill side to side rather than top to bottom.

Just a thought.

Cheers,

Gus

[Forrest747]

i wouldnt worry looks good, but if you must do something than do a square 1/8 inch gussest on the side where the tongue and top frame come together. just my 2 cents.

Now for me I did the same thing is i welded and then added bolts.

[KCStudly]

If like you (OP) said the welds are of good quality, then you can compare the cross sectional area of the weld to the expected load, and/or the cross sectional area of the tubing.

Mild steel has a yield strength of 36kips (36,000 lbs/in^2), but it is normal to assume 24kips as a 1.5 factor of safety.

Look at your expected tongue weight, figure the ratio of length between your tongue extension and your tongue overlapping the main frame (the leverage), multiple x10 for an assumed dynamic factor (that really big bump or pothole), then compare to the area of weld x 24kips. Not an exact science, but it should give you an idea if something is way out in left field.

Don't over estimate the size of your welds. They may reach up or to the side by 3/16 or a quarter of an inch, but it is the thickness midway on the fillet that matters.

Shoot us some numbers from your actual set up and we can do the math. No guarantees, just another way of looking at it for TLAR (That Looks About Right).

Tongue sticks out in front of frame = ?
Tongue overlaps frame = ?
Length of weld between tongue member and frame member (each side) = ? (if they are different curb side or street side just give us the shortest one)
Size of weld extending down tongue member = ?
Size of weld extending along bottom of frame = ?
Is weld rounded out away from weld, more or less flat, or dished in?

To be honest, I didn't bother doing this for my frame. I just welded it all the way around with some pretty beefy welds and a good strong tie in at my rock sliders.

[angib]

Although I often seem to be the doom-sayer on this forum, in your case I'll switch and say that you haven't got anything to worry about - a decent quantity of chewing gum would provide the strength you need.

The weld at the front cross-member doesn't matter* - if it were to happen, failure of the tongue will always occur with the coupler going up and the front of the trailer going down, so this joint is in compression and the weld isn't increasing its strength.

At the back end of the A-frame, with the good amount of overlap between A-frame and main frame that you've provided, the load on the rear joint isn't great. I would guess that the maximum possible load on each joint is 500 pounds and that sounds a lot, but isn't much for a couple of welds. I don't believe adding bolts at the rear joint would increase its strength significantly. Adding bolts to the front joint will weaken the A-frame significantly.

If you want to be a worrier, the one thing to watch out for is cracking over time - the A-frame or tongue gets a cyclic loading, so fatigue can be a concern. Once a year, crawl under the front and have a good look at those welds with a torch. If there are no visible cracks, you're good for another year.

* As an aside, the Australians say that the A-frame to front cross-member joint must not be welded at all. I believe this is because they have a lot of washboard roads and so the weld-induced stresses increase the likelihood of fatigue cracking. I think that's going a bit over the top, but a cautious approach would be to only weld the longitudinal welds at this joint - that's the ones that would be visible in that 3D illustration - and not to weld the transverse welds across the top of the A-frame members - those ones would be hidden in that illustration.

[KCStudly]

...have a good look at those welds with a torch.

For those unfamiliar with The Queen's English, in this case "a torch" refers to a flashlight, not "the smoke wrench".

[Treeview]

...or gas ax

[jdaan]

Thanks for all the replies. I think I've reached the conclusion that I'm worrying a little too much, but that there are things I can do if I want. My first big trip (3000+miles) with the trailer is next month, and I'm trying to resolve all the worries before then. The total trailer weight is only about 800-900 pounds (I think), and the frame certainly seems sufficient for that. I'll check the welds for stress as I go. I forgot to mention that the trailer is nearly complete, and removing the body of the trailer to add welds/bolts at this stage would be a bear.

Here's a pic of the trailer so far


Thanks,
Justin

[Treeview]

FWIW...YMMV

I've owned bigger trailers...that hauled heavier loads...with less robust tongue/frames...and never had a breakage.

To find a someone who worries more...give a listen:

http://www.youtube.com/watch?v=j0e10baH6cE

Tom

[48Rob]

justin,

Nice profile!

When I first started, I worried about a lot of things too.
The big one was a spare wheel and tire. The trailer was a vintage model, and I scrambled the last week before the maiden trip to find one that would fit.
We loaded up the newly purchased tire and wheel combo, and went on out 700 mile trip.We pulled that trailer many thousands of miles before selling it.
We never had a flat...

Several trailers later...we don't even bother with a spare. all our trailers are built with concern for quality in general, and all get new tires.

Hope you have a great trip with your new trailer!

Rob

[jdaan]

2 1/2 weeks, 3700 miles without any problems. I finally started to relax at about 1000 miles.

Here's a pic from the road.



Justin

[Corwin C]

2 1/2 weeks, 3700 miles without any problems. I finally started to relax at about 1000 miles.

Here's a pic from the road.



Justin

That's a fun section of road (Head of the Rocks between Escalante and Calf Creek) ... hope you enjoyed it.