Rectangle tubing for gooseneck frame

[achirdo]

Starting to get my ducks in a row to build myself a new trailer. I am fully capable of building a HD trailer, AWS D1.1 certified, insured, Yada Yada. Now that's out of the way, I'm wanting to build a 20-24' gooseneck trailer out of some left over material I have from a job. I currently have 2 20' pieces of 6x4x3/8 rectangle tubing. And a bunch of 6x4x3/16 I can use for the cross beams. I'm trying to determine if this will make a decent frame material. Im in North texas so well away from heavy salt usage. I guess one of my biggest worries is making this trailer too stiff. Isn't a little bit of flex in the frame preferred to it being completely rigid? I'm assuming a torque tube down the middle wouldn't be necessary? Any input would be great. Probably will still make the neck out of either channel or I beam.

[idacal]

i rebuilt a neck on a trailer I had with 4by8 by .250 tubing it stiffened it up, noisy towingempty but it sure is nice to tow. if your going to build an over the wheel deck you are going to have some funky looking spacers to mount the axles to. Deffinetly look home made but free material I would be tempted to do it. i dont think you will like having an Ibeam neck tied in. all your flex will be in tha one area but even with free material your still going to have an astonishing amount of cost in it least I always do. i mean if your building it why not put hydrualic braked, torsion axles under it. boom there goes your budget

[rexcormack]

What maximum weight do you plan on hauling on it?
That dictates EVERYTHING else.

[cd19]

I think you will find that A: the size you have is not going to do the job on that length and B: tube in that application is going to be more weight and money than can be had in I beam. You could truss the bottom and probably be happy but since that is the foundation I'd just suck it up and buy the beam.

[achirdo]

What maximum weight do you plan on hauling on it?
That dictates EVERYTHING else.

I was planning on putting dual 8k axles under it

I think you will find that A: the size you have is not going to do the job on that length and B: tube in that application is going to be more weight and money than can be had in I beam. You could truss the bottom and probably be happy but since that is the foundation I'd just suck it up and buy the beam.

Why do you think it wouldn't do the job? I already have The 2 pieces of 6x4x3/8 react tubing needed for the the frame. You really think I'd be better off not using them and buying 2 new pieces of I beam?

[achirdo]

What maximum weight do you plan on hauling on it?
That dictates EVERYTHING else.

i rebuilt a neck on a trailer I had with 4by8 by .250 tubing it stiffened it up, noisy towingempty but it sure is nice to tow. if your going to build an over the wheel deck you are going to have some funky looking spacers to mount the axles to. Deffinetly look home made but free material I would be tempted to do it. i dont think you will like having an Ibeam neck tied in. all your flex will be in tha one area but even with free material your still going to have an astonishing amount of cost in it least I always do. i mean if your building it why not put hydrualic braked, torsion axles under it. boom there goes your budget

I was already wondering what I was going to do to space out the axles down further. I have some 8x4x1/4 rect tubing also I was thinking about using.

[idacal]

were you thinking of a 20' or a 24' ? it seems like a long distance on a 24 between the front of the first axle to the neck on 6" tall material even 4 runs of it but you are 3/8" thick though probably still be as stiff as the standard 12" beam thats normally used but it will be a heavy trailer for what it will be. I like the one I built the neck on because I can overload the front of the trailer and not bend the trailer like the rest of mine are. also a dove tail is nice if loading wheeled stuff see how this keeps getting more complicated? these axles just came up locally and I have been trying to figure out how to use them but nothing I have has air https://boise.craigslist.org/hvo/d/2...596047352.html

[cd19]

Yes I do think for a 16K trailer you would be better off buying beam. Beam and tubing are very much different. if your tube was 4x10 or vicinity you could get me on board maybe but not 6x4. Just because you have something doesn't make it right.

[Todd496]

I am not a big fan of box tubing frames although there out there. I just stretched a trailer and there are a lot of suspension parts for tube style frames. I would use the tube for the main frame but not the cross members. I also would not weld the cross members in solid. That's my 2 sense.

[cd19]

I am not a big fan of box tubing frames although there out there. I just stretched a trailer and there are a lot of suspension parts for tube style frames. I would use the tube for the main frame but not the cross members. I also would not weld the cross members in solid. That's my 2 sense.

Yes it has to be able to flex as well.

[diesel625]

I’ve used tubing for frames. 2x8 worked well for what I used it on. I would rather use I-beam than tubing. If the tubing had a larger web, it would be fine I’m sure. When you load the trailer tongue heavy, your probably going to wish you had used I-beam, or channel iron. I rebuilt the neck on a 20ft 14k flatbed gooseneck that previously had a 2x8 neck. I replaced it with 10”x15lb beam and couldn’t be happier. The 2x8 was 1/4 wall.

[richey]

Back in the late 70,80, and early 90s I owned a company that specialized in trailers up to 600 Ton Capacity. We fabricated a lot of trailer frames out of A-514 ( T-1 ) Steel 100,000 to about 110,000 tensile strength if I remember correctly. We built a lot of trailers in the 200 Ton and down to 6 ton for specialized applications. One Trailer we built for a company was built to load a 170 Ton Crane from the Side Rail of the trailer. In other words the crane could not be loaded from the front or the rear. It had to load from the side. The Trailer was close to 16 foot wide . The rocker beams for the massive axle system was cut from 6 inch think plate. The rockers were 8 to 10 feet long that articulated in addition to rocking.
( If I can find it since our down sizing of our home and moving) I have a photo of the crane sitting on the trailer. The floor was 8 inches thick. Yes all of the special lowbed trailers had a lot of calculations performed by our 3 engineers to make sure we didn't build a lead sled.

The purpose of this post is to make you aware that a lot of the same principles apply regarding most trailers that are built. In other words if you can find someone on this site that can run you the sectional modulus of the tubing that you are planning on using then they can calculate the amount of deflection that your trailer will have. Sometimes throwing more steel at a project does not solve the problem. I like your idea of building a trailer with the paid for materials on hand but sometimes in the old days when I started out I did the same thing and wound up not getting what I though I was getting.

Just a suggestion that you might be better off to sell or trade the tubes and buy some grade 50 (A572 beams) of perhaps the depth that you need. The tubing that you described will maybe weigh about 22 lb per foot if I remember right . A 10 or 12 inch beam around 22 lb per ft should give you a better trailer. Remember Figures don't lie so I make the suggestion that you ask the folks on this site to help you run the numbers. Get someone to do the figures. I honestly believe with The amount of folks on the site with all their talent that someone can help you. I learned a long time ago to use my resource people. This is just my humble opinion . I sold the company in 91 and have forgot a lot of the formulas.

Good luck with your trailer and keep us posted on how you arrive at your finished product. I bet you get it figured out and come up with a really nice trailer that you will be proud of for years to come. Richey

[CrookedRoads]

I rebuilt the front section of a very large and expensive fifth wheel travel trailer that was in an accident and it was all made from rectangular tubing. I don't remember the size of the tubing but I do remember it was a real pain trying not to burn down this trailer in the process. Also you can take a look at the big semi car haulers, their all made from tubing.

[TWeatherford]

A travel trailer is a significantly different load than an open equipment trailer - ie point loads with straps/chains pulling on the frame vs a pretty well distributed (and relatively light weight) load of a travel trailer. Semi car haulers look a lot more like a truss bridge than most equipment trailers, and they're carrying stuff that has a suspension, etc etc. Just because something is works in one application doesn't mean it's good or ok in another.

I'm a mechanical engineer, and would not consider building my own trailer if it was ever going to see the road (I have no problem building stuff that stays on the farm). There are simply too many unknowns and a mistake that stands a reasonable chance of hurting or killing someone in my opinion is not worth the savings of building vs buying a trailer. I am confident that a decent lawyer could make almost anyone look like a fool on the stand, after as much as a license plate frame comes off a homemade trailer and hurts someone.

The very thought of building something with some flex, vs rigid (nothing is rigid when it comes down to it, and the difference between plastic and elastic deformation is critically important), should give some pause as to whether one is qualified to calculate flexibility and then design, build, and test a trailer. I am not. It is far more complex than designing to achieve a certain maximum amount of deflection with a static load - dynamic loads while going down the road (curved interstate exit ramp, panic stop or 'hit a freight train' stop, compact car sized potholes) place significantly different loads in many directions other than down than a simple static load does.

Trailer manufacturers design, build, and test on the lab and on a closed course or they overbuild significantly and de-rate the load rating. Then redesign and repeat based on their findings. They can make a frame lighter and cheaper because they have a lot of knowledge of what they're doing. To build 1 prototype, and put it into service, requires significant design time. To do it with any kind of safety, by someone without a lot of design experience, requires a frame so overbuilt that it just makes no sense vs a purchased trailer which is lighter and easier to use.

I realize I don't have a lot of posts and am not well known on this board, and some will write me of as one of those darned engineers over complicating a simple problem again. I think a lot and can't understand the confidence some have in their abilities. Most of the pictures I see are of very good fabrication, and well thought out designs by men and women who can really get something done. The welding in particular is usually far better than I can do, but if the pieces being welded together aren't big enough in the first place it doesn't matter how many welding certifications someone has. I think that building trailers involves more than most realize, which is the point of my post.