Harbor Freight Trailer Weld Fail

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Re: Harbor Freight Trailer Weld Fail

Postby Bogo » Mon Dec 05, 2016 2:23 am

The problem with welds is they can weaken the metal right next to them. A poor quality weld on a minimal sized frame or tongue members can easily reduce the strength significantly and make failure likely. When I was designing my ttt design a friend said to not let welds any where near the joints between the tongue and frame because they are some of the highest stress points on the frame. He also said all bolt holes need to be in the middle third of the vertical webs of the frame members unless the design takes them into account. None on the top or bottom faces unless the overall strength of the member was increased to account for them. If necessary, use a bracket to transfer the load between the tongue and frame. The problem with putting a weld or bolt hole through a top or bottom face of a C-channel, I-beam, U-channel or box beam is those operate in tension and compression so any change in strength will be a stress point, and may lead to failure there. On the other hand, the vertical webs just operate in moderate compression and tension in the middle third of their height. The top third can be thought of as part of the top face, and the bottom third as part of the bottom face, and thus are under high tension and compression. This doesn't mean you can knock large portions of that middle third out. it just means that putting a 1/4" diameter hole in the middle of a 2.5" high web may only drop the overall beam's strength 5% instead of 10%.

I ramble a bit, and I'm no metallurgist or engineer, just wise enough to seek out and listen to what they have to say.
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Re: Harbor Freight Trailer Weld Fail

Postby QueticoBill » Mon Dec 05, 2016 8:32 am

BOGO - good and thoughtful points but be careful in assuming all channels or other shapes are always loaded in the X axis with flanges seeing the most stress. Sometimes they are used the other way.

Clearly, as can be gleaned from reading tnttt tongues are the critical element. I'm not worried about the minimalist frames of the common utility trailers, especially with the deck and box attached. I do plan to add an extension to my NT and probably take it back as far as possible without interfering with axle, and may have it welded. And at that point, why not tack all the joints and add some simple gussets at the corners.
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Re: Harbor Freight Trailer Weld Fail

Postby dmdc411 » Mon Dec 05, 2016 11:56 am

I agree with metal fatigue as the cause. I also feel after having looked at these trailers at HF, they are marginally adequate. That wasn't enough in my view. My neighbor has one with a wood box mounted for running yard waste. I've done more repairs to it than you can imagine. Yes, it's carries grass, brush, firewood. But, only 4 or 5 miles of ok roads. For supporting a camper weighing 1500 plus pounds, that's not enough.
Now, for repairs, nested angle, or boxing the frame. And weld it all. How, that's the problem. You have to deal with flammables. Look at the design library for the tongue mod.
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Re: Harbor Freight Trailer Weld Fail

Postby bobhenry » Tue Dec 06, 2016 8:08 am

Namco , Carry all, and other cargo trailers all have the problem that they rely on the front cross member and the next to do all the work. This means that the second cross member has all the down force. My Namco I purchased used, had a definite bow downward on the second cross member. I have replaced all the trailer tongues with 2" square tube but ran it all the way to the rear reducing the teeter totter effect the tongue suffers by allowing the new longer tongue to share the forces with all the cross members. I truly don't think it's the metal as much as the poor design.
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Re: Harbor Freight Trailer Weld Fail

Postby QueticoBill » Tue Dec 06, 2016 9:49 am

bobhenry wrote:Namco , Carry all, and other cargo trailers all have the problem that they rely on the front cross member and the next to do all the work. This means that the second cross member has all the down force. My Namco I purchased used, had a definite bow downward on the second cross member. I have replaced all the trailer tongues with 2" square tube but ran it all the way to the rear reducing the teeter totter effect the tongue suffers by allowing the new longer tongue to share the forces with all the cross members. I truly don't think it's the metal as much as the poor design.


I wanted to do that - tongue to rear of frame - with my Ironton but it seems after inverting the axle to above springs, the 2 x 2 won't be clear enough above axle. I was planning on going back to 3rd of 5. I am attaching 3/4 plywood deck directly to the cross channels with tek screws, and I felt the deck would be plenty strong to brace all of the framing. I am upping the 2 x 2 a size - 1/8" is OK per spread sheet in design resources - with very conservative large estimates so going to 3/16". When I look at some of the early plans with all wood frames and don't ever recall hearing of those failing catastrophically, it seems very OK.
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