Drawbar attachment methods

[MickinOz]

This was probably covered in the pinned tongue strength post above, but the links don't work for me.
It seems a lot of guys who build their own frames just butt weld the drawbar a-frame to the front face of the front cross member of their rectangular main chassis.
If they put a centre longitudinal piece in, this often gets welded to the front of the chassis, too.

Butted on A frame.JPG (48.02 KiB) Viewed 1497 times

This isn't the strongest of methods, in my view. The A-frame will always be exerting some twisting force on the front cross member and trying to tear the butt welds.
My a-frame is somewhat like this and it bugs me a bit.

Would be somewhat better if a brace/gusset was place underneath to reinforce it.

Reinforced underneath.JPG (40.36 KiB) Viewed 1497 times

But I think the thing is best built with the rectangular main frame, a-frame out the front and that centre longitudinal drawbar passing under the lot.

Centre brace passes under frame.JPG (37.29 KiB) Viewed 1497 times

Or just do it a la NT and HF trailers, but welded from decent size material rather than bolted together aluminium foil.

If you look at Tony Latham's plan, the whole lot passes under the main frame. Much better distribution of the forces at play, I think.

[QueticoBill]

The pass under and diagonals also passing under first cross piece and anchoring under side rails would really beef up the whole frame. My straight tube extends to third cross piece. The frame even though bolted not welded is very rigid. It does restrict a dropped floor, not something I ever considered.

[saywhatthat]

sadly most people build their frames like they're going to haul two or three battleships. trailer frames and semi frames were built out of woods up until the thirties and the ultimate off-road vehicle covered wagons.
A gentleman named Andrew he designed some lightweight frames for this form we use them in a rental fleet
They've been rear-ended and dragged on the Rubicon Trail and they still seem to keep on going.
the biggest problem we see at the shop people that keep jackknifing them and work a small crack and don't look there trailer over now then so no need to over think it https://offgridspot.com/wp-content/uplo ... welded.pdf
https://offgridspot.com/wp-content/uplo ... welded.pdf

Teardrop_Camper_Plans_–_11_Free_DIY_Trailer_Designs_PDF_Downloads_-2-min (1).jpg (53.34 KiB) Viewed 1442 times

[QueticoBill]

Saywhat - I agree and the simple frame you show makes sense for some builders. The strong enough design is often overlooked for the as strong as possible design. Easy to overbuild.

But I do wonder about designs with lightweight platforms and foam walls. The "classic" ply wall must add a lot of support to the "corners" of a platform on that wishbone frame, and support the cantilevered "tail". Foamies may need a stiffer and more complete frame.

PS. My frame is overbuilt but at this point it's being used as an utility trailer, with no cabin "box" to support the floor.

[tony.latham]

most people build their frames...

What suspension do you put under yours? Is that a torsion axle?

We take ours off the beaten path ... a lot. Rough rocky roads. Lots of twisting forces on the chassis.





Tony

[Ottsville]

I'm going to agree with Saywhat here in that most of us overbuild for what we are hauling. That A frame design is probably optimal for most TD builds. I would think the next best in terms of ease and not overbuilding would be a single square tube tongue that runs under the frame and back at least to the second crossmember. Butt welding the tongue to the front crossmember seems to me to be a bad idea structurally, and even more so for non-professional welders.

Tony, it looks like your diagonals go under the front the crossmember, ending at the side rail. This is the way many utility trailers are built (Tony, does yours have a central spine also?) . I would think that short bit of diagonal helps to brace the frame in square, though y axis torsional forces on a TD should be small.

[tony.latham]

Tony, it looks like your diagonals go under the front the crossmember, ending at the side rail. This is the way many utility trailers are built (Tony, does yours have a central spine also?)

It's not going to bend.

Tony

[Tom&Shelly]

I'm going to agree with Saywhat here in that most of us overbuild for what we are hauling.

Absolutely what we did! It worked for a hundred others on this forum, and the frame seems like the worst place for novices to experiment!

Sure am glad there are those of you trying new things though. In the (unlikely) event we build another, we'll probably be looking at building a bit lighter and maybe more daring (engineering-wise).

For those with some knowledge of military aircraft design--I like to think we built our teardrop like an airplane, not a tank. Like a Republic aircraft!

Tom

[swoody126]

DEFINITELY a fan of Tony's method

stop by your local utility trailer yard and check them out

only rarely will you ever see one w/ the "A" frame butted to the front of a rectangular frame

Tony's experience(s) should be heeded in this old man's opinion

sw

[saywhatthat]

Bill

But I do wonder about designs with lightweight platforms and foam walls. T

are trailers are foam /glass
Tony

What suspension do you put under yours

torsion axle . ON the hard core trailer we use springs and beam axle .That way if something breaks can get fixed easily .
My I suggest before many people build their trailer frame go look at some of the tent trailers probably the least supported by the box that sets on top of it
Something is wrong when you have more Steel in your trailer frame that just being dragged than your toe vehicle

[working on it]

...What suspension do you put under yours? torsion axle . ON the hard core trailer we use springs and beam axle .That way if something breaks can get fixed easily ....

* Agreed heartily with that! OVERBUILDING is better/safer/more reliable than trying to save weight here and there (on the frame, running gear, and cabin construction), de-rating torsion springs to achieve a marginally softer ride (of the un-occupied teardrop/squaredrop trailer, and later finding out that they've weakened over time, and must be replaced...maybe in the boonies). Time-tested spring axles are the easiest to customize, repair, or replace...anywhere.

* I made my squaredrop from a single drawbar-type motorcycle trailer, adding rectangular steel tubing to extend its' length to 8'. I replaced the bent original tongue with 6' of 3" square tube, .188 thick (plenty of strength for highway use), and to prepare it for off-road use (if ever), sisterred-in rectangular tubing full-length to the rear of the trailer, above the tongue (which was also joined to three crossmembers, for extra strength).

3 crossmember tie-ins, plus sistered sections.PNG (397.2 KiB) Viewed 1330 times

* And later, when changing the original light-duty axle to a 3500 lb braked axle (with 3000 lb springs), I reinforced the frame rails with 1/4" x 2" angle steel. Maybe overkill, but it will last. I stayed with the single-beam tongue, considered welding side pieces to make it an A-frame if I really went off-road, but never did. The side pieces (as seen in my signature's lead photo) are thin steel angle stock bolted on, that just serve to stabilize the sliding tongue box platform. The single-beam is good enough for soft-roading.

[QueticoBill]

I just don't see overbuilding is better for the user if the not overbuilt design does everything its asked to.

[Tom&Shelly]

I just don't see overbuilding is better for the user if the not overbuilt design does everything its asked to.

Ruin a trip pretty fast if it doesn't.

Of course, you'll never know ahead of time where the exact line is between "not overbuilt" and "underbuilt". Life is like that.

Tom

[QueticoBill]

So you would maintain all cars, skyscrapers, airplanes, and most other things are overbuilt since they rarely fail. I just don't believe they are, and it is possible to plan them so they are strong enough.

[Tom&Shelly]

So you would maintain all cars, skyscrapers, airplanes, and most other things are overbuilt since they rarely fail. I just don't believe they are, and it is possible to plan them so they are strong enough.

Overbuilding is part of the planning. It's called an "engineering safety factor": https://en.wikipedia.org/wiki/Factor_of_safety

Of course all well engineered things are overbuilt. Even when stresses are "calculated to the n-th degree", the engineers apply a safety factor.

Most of us don't calculate the stresses on our trailers that precisely, so the safety factor is less formal. If you search back through this forum, you'll see two or three cases where someone got it wrong. To say it ruined their day would be a crass understatement.

Tom