Frame design for new build

[brian_bp]

I have the same reservations about welding directly to a Dexter axle, based on what I've read here. One way around that would be to have a 2x2 tube x-member and axle stubs welded to it, although apparently that's a bit complicated to get lined up properly. Here's a revised single tongue drawing with a 2x3x1/8 tongue mounted "sideways" and a 2x3 x-member. The weight on that without the axle is around 83 lb. Next to it is the simple a-frame design weighing in at 71 lb.



Does it make more sense to use the 2x3 cross-member for the forward one?


Justin

I like the A-frame... and I think that's been hashed through a few times.

If the tongue is straight, extending it to the axle tube instead of a regular frame crossmember makes sense with a suspension having such a fixed tube; the U-Haul rental travel trailers were built this way.

The U-Hauls had brackets welded to the axle tube, which leads to one of two possibilities:

the welding right at the centre is far enough away from the rubber that it is not a problem; or,
the bracket was welded to the tube before the axle was assembled.

In any case, an entirely bolt-on bracket (welded to the tongue, bolted to clamp around the axle tube), seems like a practical approach.

As for the laid-flat 2x3... this make some sense to me. The SAE standard for hitches (J684) specifies the same required strength laterally and vertically: 50% of the full trailer weight. Since the tongue weight is typically only about 10% of the trailer weight, perhaps they didn't feel it was necessary to get more specific than that. Weakness - the tendency to break - is bad, but softness - the tendency to bend like a spring - is not so bad. Perhaps vertical softness (which would allow some pitching) might even be more tolerable than lateral softness (which would allow some yaw, or sway), so a big strong rectangular pole tongue might be better laid flat, instead of bracing it.

I still think that the A-frame is structurally much better, and preferable unless severe turning angles are desired.

[asianflava]

I'd be more concerned about vertical strength than the shimmy. My 5x10 with a 2x2x1/8 had a slight shimmy but it wasn't that bad though. Some roads that I've encountered have just beat up the trailer tongue. Concrete freeways with expansion joints seem to be the worst. The added stiffness of the 2x3 plus the lighter weight of the trailer should take care of the shimmy, the 2x3 is 7000in-lb stronger than the 2x2 in the lateral direction.

There was no rhyme or reason to where I placed the cross member. I just wanted to make shure it was at least 3 ft away from the front so that it would provide good stabilization for the tongue.

[brian_bp]

While a single tongue is neat and clean (at least it is with nothing mounted on it) if you ever do plan to mount something there (battery box, generator, etc) it's much easier/neater to do with a Vee tongue

My Little Guy has the single tongue and I have all sorts of plans for mounting stuff up front, so I wish it have a Vee instead

Don

Don's real experience (in practical aspects) and my theoretical preference (regarding structure) seem to agree here.

For anyone with a pole tongue and wanting to mount a single propane tank, U-Haul had a nice-looking solution for that... it's a vertical post with the tank strapped to it, but I have not found a useful photo.

[Trackstriper]

The reason I threw out my 2 cents worth last night regarding a single tube tongue was that Justin liked the looks of it. Aesthics can rule what we do sometimes. I would build it with the A-frame, 14 gage 2x2 as he proposed.

Regarding the welding of a "supplemental bracket" to the axle tube, Dexter could void their warranty if they decided that it did something to affect the axle, says so in their on-line literature. I don't know how far the rubber extends into the axle tube, my guess is about 12", 15" max. Look at the size of the available half-axles in this weight range, they're not very long. My 1400# Flexiride half-axles have a rubber core about 9" long. I'm thinking there isn't much difference in how far the rubber extends into the axle tube between different brands (although the Flexiride system works slightly differently).

The amount of heat transmitted down the axle tube from a bracket being welded at the middle would depend upon how quickly you wanted to make the full weld. You could tack it, run two inches of bead, let it cool, then repeat. The axle could be wrapped with wet towels 6" either side of the weld to suck up heat if you want. I'm sure it can be done without hurting the rubber or warping the axle tube.

Look under a small cargo trailer with rubber torsion suspension that was built by one of the larger manufacturers. Do you see Dexter's hanger bracket welded to the frame with the axle bracket bolted to it, nice and neat, or do you see the basic mounting bracket welded directly, contra Dexter's specific recommendations? I can tell you how Pace built my old 6x12 trailer, but it's good to get under a store bought trailer once in a while. Sure, you could pour some heat into a weld at the frame/bracket junction and certainly harm the rubber. The proper hangers would be best, and I'd do it that way probably, but there is some grace left in the system for someone to "judiciously" weld the axle bracket directly to the frame. Slowwwwly, little at a time. I wouldn't even think about welding anything to the axle tube in this area though, that's a little too close.

BTW, Rocky, sorry I repeated your observation about one stick of tubing taking care of the perimeter frame, I'll blame that on my brain late at night!

Justin, hope all this discussion will help you with your decision.

J.B.

P.S. Put me in the "broke a tongue" club. I lost one maybe thirty years ago on a small, open 4x6 utility trailer. It was a factory frame that had a slight vertical "S" bend to the tongue and it just slumped to the pavement at 60mph while driving on a lumpy interstate in our favorite hurricane prone state. Made a pretty good racket. I think water may have accumulated at the bottom of the "S" and allowed rust to form internally. I was able to field repair it to get it home. Put about 100k miles on that little sucker.

[jdaan]

It's becoming clear that the lightest, strongest option is most likely the a-frame design of 2x2 1/8 tube, and a 2x2 14gauge perimeter. I'm willing to set aside my preference of a single tongue for a simpler design with more options down the road (tongue box, etc). Thanks for the help puzzling through the single tongue option.

One last pic of what I think will be the final design.



Thanks for the help figuring this out! I'll post pics as soon as I have it made up.

Justin

[WarPony]

Good move, Justin. I like the last design you have, too.




Jeff

[brian_bp]

Great, Justin.

Now just make sure that the A-frame ends meet at 50 degrees, so the a common A-frame coupler will fit nicely. I think that I would clamp the tongue up to the frame with the actual coupler in place before welding just to be sure, but others may have better suggestions.

[Bigv]

wow you guys answered alot of questions i had, I like the single tongue the best and plan on building a 5x10. Good luck guys and thanks.

[jdaan]

I'll make sure the welder has the 50 degree coupler before welding the a-frame. One issue I had in figuring out the frame is that with a narrow frame (4x8), the 50 degree angle limits the length of the tongue. I wanted a longer tongue, and with the a-frame I can only make it about 38 in. and still have enough under the frame to weld it securely. I was shooting for 42 in., but 38 is fine. I know Madjack came up with a solution by bending in the ends of the tube to 50 degrees, but in an effort to stay simple I'd like to avoid that.

Bigv - let me know how the single tongue works out. It's still my favorite design aesthetically.

Justin

[angib]

Weakness - the tendency to break - is bad, but softness - the tendency to bend like a spring - is not so bad. Perhaps vertical softness (which would allow some pitching) might even be more tolerable than lateral softness (which would allow some yaw, or sway), so a big strong rectangular pole tongue might be better laid flat, instead of bracing it.

I tend to agree with Brian, though I've got no evidence to back it up. I believe that those tongues that break always do so vertically - so that suggests that vertically, strength is the most important. But I think it's only horizontally that a serious shimmy can develop, so that supports the need for horizontal stiffness. I think I'm tending towards the large square tube as the best option as that covers both bases!

The issue with single tongues is that while failure, if it happens, will usually be vertical, any horizontal shimmy will stress the tongue at the same place and so that can contribute to starting a fatigue crack that eventually fails.

To repeat what I posted in another thread recently, A-frames have two advantages:
- they are much stronger horizontally than any single tongue can be;
- they connect the coupler directly to the strong part of the trailer, the side rails.

On the issue of using bigger cross-members with a single tongue, I think it's like this:
- the front cross-member will carry a much bigger load than the second cross-member, so it might seem sensible to reinforce that;
- but on most designs, the front wall of the trailer body is sitting right on the front cross-member and (contrary to what a lot of people seem to think) that ply wall is at least as strong as the steel cross-member, so it reinforces it a lot;
- in practice, all the reported failures of cross-members are of the second cross-member failing downwards, though this has only happened where the front and second cross-members were too close together.

As a rough rule of thumb for single tongues, I'd say that the distance from the front cross-member to the second cross-member needs to be at least half as much as the length of the tongue sticking out beyond the front cross-member.

Andrew

[Bigv]

Well it does seem that the A frame tongue is stronger. It just does not look as good on a tear. At least to me. Looks seem to be very important not just to me, but to many on this forum. I do understand now that if a person was going to add anything to the tongue a A frame is almost a must.
Wow you guys make it so a person just does not know what to do... It seems that the more knoowlede I get from you guys the harder my frame decision is. lol thanks all.

[G-force]

Forgive my crudeness, but we are not building a piece of art to stick on a wall and admire...we are building half ton structures towed at freeway speeds that are easly capable of killing many people if they seperate and run into oncomming traffic. Indeed, "Looks" is pretty far down my list of frame requirements. If you really want a single tube, go with one stronger than you need, perhaps 3x3 with a 1/8" wall, and a suitably strong frame box and crossmembers to attach it to? The difference between an ultralight questionalble frame, and one built like a tank is probaly less than 50-100 pounds. Really, is that extra weight going to matter?

[bobhenry]

Forgive my crudeness, but we are not building a piece of art to stick on a wall and admire...we are building half ton structures towed at freeway speeds that are easly capable of killing many people if they seperate and run into oncomming traffic. Indeed, "Looks" is pretty far down my list of frame requirements. If you really want a single tube, go with one stronger than you need, perhaps 3x3 with a 1/8" wall, and a suitably strong frame box and crossmembers to attach it to? The difference between an ultralight questionalble frame, and one built like a tank is probaly less than 50-100 pounds. Really, is that extra weight going to matter?

Well said !

I am a bit concerned with my hybrid frame. With Chubby approaching the max for the HF axle and tires I see a bit of flex in the HF stock tongue as well. I intend to run a center 2x2x3/16 from about 18" ahead of where coupler is now and it will run clear to the rear to be modified into a receiver. I have jacknifed the body of the tear into my utility bed truck once and by extending it thru the existing "a" tongue they will work together with the "a" helping to dampen sway while the center tube will add to the tongue strength.

[jdaan]

G-Force - I agree that we need to prioritize safety before style. However, I think lightweight (even very lightweight) and safe are not mutually exclusive. I'm trying to make a frame that exceeds the strength requirements for my proposed 800lb tear, without going overboard just for the sake of overbuilding. One thing that attracted me to building a tear is the combination of style and function. I think it should be a work of art as well as a safe, functional camper and trailer. Your post was a good reminder of what is most important, though.


Having said that, the a-frame design posted above is meant to exceed strength requirements for my tear, but is still sparse and lightweight. Not being anywhere near an expert myself, I'm hoping the members of this forum will point out any red flags they see. I don't want any of you afraid to be driving behind me on the freeway!

[Bigv]

WOW cool down G-force lol. I was just saying I like the single tongue best. And I know many on this site who built with a single tongue... I know just from my few months of being here on this site looking and learning everyone cares about safety.

I will build my tear with a single tongue. That is what I like best and no one with any real knowledge has told me it is not safe... I have been asking and learning how do I Bigv, make what i want safe and possible. For me looks is most important. If i can not have the looks i want I will not do it. If my brain can think of it, I know that some one on this site can help me make it my way and safe. This fact only took me a week of looking at all the sites on how to make a teardrop trailer... and this is the only site I have become a member of.