I'm building an off-road camper. I've spoke to welders, fab shops and a couple trailer builders about materials to use for the trailer. Well, I got different answers so I tried to use strength and data sheets to calculate what I needed. Because of design I don't know if I'm applying the various calculations properly. The camper shell will put about 800 pounds on the perimeter of the trailer. Can anyone tell me if I'm on the right track?
Correct material for new trailer
- Thread starter Willgyver
- Start date
PugetDude
ALLIANCE MEMBER
I'd probably bump the 1" tubing up to 1-1/2" and drop it down to 14 gauge.
But, that's just me.
But, that's just me.
readhead
Well-known member
I would agree. Also reinforce the tubing at the axel mounts and any other potential stress points.
Walkers
Well-known member
Off road and 1" tube don't really go together.
nadogail
Well-known member
Can you look at a commercially made trailer and make yours just one step stronger? Trailer makers build their trailers to survive, just make yours a little bit better.
billconner
Well-known member
I think 2" tube is more common, but simpler layout.
You really ought to check tnttt.com - teardrops and tiny travel trailers. There are folks there that seem to build new trailers every year. They also have plans.
You don't want that A-frame joint at the front of platform. Weak point where trailers fail. Let the diagonals continue to side rail, which also braces basic frame.
You really ought to check tnttt.com - teardrops and tiny travel trailers. There are folks there that seem to build new trailers every year. They also have plans.
You don't want that A-frame joint at the front of platform. Weak point where trailers fail. Let the diagonals continue to side rail, which also braces basic frame.
Hohn
Well-known member
Hi Will--
I've never made such a trailer, but many of my fellow engineers at work are into off-roading and I've seen their setups and what works.
I think you want rectangular tubing, probably 1x3 11ga (.120 wall). Think two large frame rails (or one even larger spine like many flatbed class 8 trailers), then place your grid box frame on top of that.
GaryM909
Well-known member
I would use channel instead of sq. tube. I have seen a few sq. tube trailers where the frame is rusted through because of trapped moisture.
Hohn
Well-known member
Good point, but with any of the better lanolin-based rust preventative products (woolwax, fluidfilm, Surface Shield) this is easily addressed.
Daveyclimber
Well-known member
You need the modulus of a rectangle tube and the wall thickness to support torsional stress. Anything offroad capable absolutely has to be over built and engineered otherwise the tubing will crack next to the weld joints and any structural mounting point. 1x3 .120 is the minimum I would use if the weight is light. Consider suspension type and mounting structure carefully. If the trailer is too light, the suspension will destroy the frame. I would also consider the tounge to frame interface carefully as well.
sjvicker
Well-known member
I considered building an off-road trailer a few years ago and ultimately decided against building it. A roof top tent and everything thrown in the bed of the truck is much more nimble but does have the drawback that you can't drop it and "hold" a site while you're out exploring for the day.
2x3 11ga for the frame rails and 2x2 11ga for the rest is what I would do and that's overkill since you're only loading the perimeter at 23lbs per ft. Look into the Timbren axleless suspension and if you decide to go that route, make sure the frame is the correct size to support their mounting pattern.
2x3 11ga for the frame rails and 2x2 11ga for the rest is what I would do and that's overkill since you're only loading the perimeter at 23lbs per ft. Look into the Timbren axleless suspension and if you decide to go that route, make sure the frame is the correct size to support their mounting pattern.
You and Daveyclimber both brought up suspension. Briefly thinking about it I thought an independent torsion suspension would be best. Are there significant differences in frame design to consider when using torsion vs axle/leaf spring suspension?
Yes, there will be a big difference with independent suspension. Go get the specifications for the suspension you plan to use. In general, I think you are way under speccing this trailer unless "off-road" means driving on a dirt road once or twice a year. Unless you are in the desert southwest, I suggest you use channel for the main frame and angle for the cross members. That will be one worry solved pretty much forever.
ez-duzit
Well-known member
Scrap the first plan entirely. Then go look at how trailers are actually built; none will look like your sketch. This will save you a lot of wasted time and material.
I vote for channel also for the reasons mentioned by others above. IMO 3 inch channel is good for up to 10 feet, any longer use 4 inch channel. You also did not mention structure of the box. If you are going to weld uprights to frame this will make a truss which will give additional strength to the frame. If in doubt, put 2 inch tubing at the middle and at the corners. One inch tubing to connect all uprights horizontally. Spacing however you planned it.
One trick for such a trailer is to weld the spring hangers to a piece of angle iron which is bolted to the side rails. This adds strength and the position of the axle under the frame can be changed easily. I have no experience with torsion axles so disregard my advice where it conflicts with that type of suspension.
KEH
One trick for such a trailer is to weld the spring hangers to a piece of angle iron which is bolted to the side rails. This adds strength and the position of the axle under the frame can be changed easily. I have no experience with torsion axles so disregard my advice where it conflicts with that type of suspension.
KEH
sjvicker
Well-known member
My travel trailer frame is very similar to this. The main difference is I have a V at the tongue but that's not something I'd be concerned about on what is essentially a beefy single axle garden trailer that also includes the tongue bar extending to the middle of the trailer and welded to 3 cross members.
Kpaige
Well-known member
Something not mentioned. Use all the same metal and stainless fasteners. Otherwise you will have corrosion issues with dissimilar metals.
I would suggest all aluminum.
I would suggest all aluminum.
mike93lx
ALLIANCE MEMBER
How do you easily coat the inside of all that tubing and maintain the coating?
I would also use C-channel. Use one continuous piece from the tongue to the rear of the trailer on each side. Like in the picture below. I'd flip the C-channel, so the flange faces in, so all you'd have to do is notch the top and bottom flange and bend it.
billconner
Well-known member
What's the load rating on that trailer? More than 10,000 pounds I'd guess. And this is for an 800 pound load?I would also use C-channel. Use one continuous piece from the tongue to the rear of the trailer on each side. Like in the picture below. I'd flip the C-channel, so the flange faces in, so all you'd have to do is notch the top and bottom flange and bend it.
mike93lx
ALLIANCE MEMBER
C channel is comical for this application. Angle iron is more than enough
Picture is just for reference as how to build the frame. I'm not suggesting he use 6" channel.
Pretty much THE WORST possible suspension for offroading!!! Torsion axles are simple, light and cheap but have no where near enough travel and articulation to work on rough ground.
Three options:
Timbren Silent Ride (here is a video): https://timbren.com/en-ca/products/...ide-trailer-suspension?variant=44708156408090
Great travel, good roll stiffness but side-to-side articulation means putting huge torsional load on the axle tubes.
One light torsion axle forward and one aft on a pair of walking beams. Similar travel to Timbren, but similar "problem" of putting differential articulation loads from one side across to the other by placing the torsion axle housings in torsional loading. Again: great travel, good roll stiffness but side-to-side articulation issues.
What I would greatly prefer to see: one pivoting tube fixed member holding a pair of independent walking beams with 4 fully independent torsion axles at each end. This gives far less roll stiffness than those above, but for offroading you will want the differential articulation travel to work for you.
If you use typical trailer farmyard junk axles (be they spring or torsion) you will tear the trailer apart from rough offroading loads - unless you build the trailer as heavy as a bank vault. And, YES, you are far better off with 2 very light axles than trying to get enough travel from one (again, walking beams being the key element)
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"angle iron is enough" Depends on the angle iron. I made a 5 x 10 cattle trailer frame from heavy 3 inch angle iron, hard steel from a piece of farm equipment, with the spring hangers on a separate adjustable piece of angle as described above. With the lighter uprights making a truss as described above plus a sheet metal strip along the bottom to keep cows from pushing their feet accidentally outside the trailer, it never moved. So, I don't think similar angle would cause the op problems
KEH
KEH
Another thing to think about: what are you doing to get torsional stiffness in the overall structure? From the sketch, and engineer's first answer will be to use tubing for frame (to give the platform some kind of torsional rigidity). A trailer builder (or an airplane builder - you would be surprised how similar the thought process is) would want the superstructure to be a semi-monocoque to provide the torsional strength a rugged body would provide for offroading. That means a metal upper frame with stressed skins to spread load across hundreds of fasteners (and/or a few square feet of adhesive). Look at a semi trailer (dry van). You might notice in many cases there is NO "frame" along it's length - the walls of the van body are a pair of giant I beams with loads fed from the shear web (skin) into a top and bottom cap strip (aluminum extrusions) and floor loads directly into bottom cap strip. Maximizing radius of gyration is the key to strength/weight efficiencies and making the whole upper structure into a stressed member accomplishes just that.
Hohn
Well-known member
"Easy" I can't say, but it's doable.
whateg01
Well-known member
You must've missed the RV and TT thread a few days ago!
whateg01
Well-known member
I think it's better to make sure moisture can get out than to try to prevent it getting in.
whateg01
Well-known member
Not that torsional rigidity isn't a factor in a trailer, but with three points of support (hitch and 2 tires) the only torsional load on the trailer is from the weight of contents and the trailer itself and momentum of those things when traversing obstacles.
nadogail
Well-known member
I have used repurposed pallet beams for projects, I sometimes acquire them for offering to haul them away. They weld well with 7014 or 6011 electrodes.
nadogail
Well-known member
Often the best material is that which you already have or can be acquired at the lowest cost and can be made to meet your needs.
I have seen many things built from repurposed steel such as bed frames or old pipe.
Often the requirements include the material be both “Good Enough and Cheap”. Labor cost on a “home made” project is often not a factor, because the builder had much more time than money.
I have seen many things built from repurposed steel such as bed frames or old pipe.
Often the requirements include the material be both “Good Enough and Cheap”. Labor cost on a “home made” project is often not a factor, because the builder had much more time than money.
whateg01
Well-known member
I would not build a trailer for use on roadways from bed frames.
metalmagpie
Well-known member
I have thought of reinforcing the area that the spring hangers weld to. Instead of just welding them to the frame channel iron, I am thinking of welding a piece of 3/8" flat bar to the channel and welding the spring hangers to the flat bar. The idea being to spread the load. I also plan to reinforce the fairly light channel in high stress areas by welding a length of 2-1/2" flat bar inside the channel flush with the flanges so as to form a sort of rectangular tube. This will help stiffen the area right above the axle.
I have made a lot of handrail with square tube. It is common practice to add weep holes near the bottom of the vertical members because otherwise they tend to fill with water and can rupture in a freeze. Very few welds are really watertight. That's why I plan to use the lightest 3" channel for my 5x10' flatbed trailer build.
metalmagpie
whateg01
Well-known member
If you are using structural channel, you really don't need to do any reinforcing. If the flange was thinner than 8 ga, I might recommend it.
whateg01
Well-known member
Why not just use tubing if you are going to box it? If you box it that way, especially before welding in your cross members it will bow outward and you'll fight it to get it pulled in straight.
billconner
Well-known member
Comparatively, this is a very light load. You may not respect the utility trailers from Harbor Freight and Northern Tools, but with camping trailer loads, they hold up for many, many years. Easy to overbuild. Hard to right size.
One of the missing details is what is the tow vehicle.
One of the missing details is what is the tow vehicle.
theoldwizard1
Well-known member
Keep your cross beams at 16" O.C. Wider will cause the decking to flex too much (unless you are using 5/4 PT decking mounted at a 45° angle).