Trailer Frame Tube vs C-Chanel

[tgreening]

Just curious but why are you so worried about humidity? I'll admit I've not traveled every town in Arizona but anyplace I've ever been was anything but humid, at least compared to back east. I'd build it out of box, cap all the ends, and forget about it. It'll likely outlast you and a couple generations more.

If you start punching holes like you illustrate, you better stick some in the bottom. If you do any water crossings you'll fill your tube up with water, at least to the level of the holes, and you'll have to wait for it to evap out unless you stick in some drains.

 

[Strider]

Just curious but why are you so worried about humidity? I'll admit I've not traveled every town in Arizona but anyplace I've ever been was anything but humid, at least compared to back east. I'd build it out of box, cap all the ends, and forget about it. It'll likely outlast you and a couple generations more.

If you start punching holes like you illustrate, you better stick some in the bottom. If you do any water crossings you'll fill your tube up with water, at least to the level of the holes, and you'll have to wait for it to evap out unless you stick in some drains.

I plan on using this trailer in other states including WA and hopefully even AK. Just thinking of everything I can, but maybe I am obsessing. It will have drain holes. Should have noted that but I was thinking about air flow within the tube to dry out quicker.

Anybody know if the holes will weaken the frame? I see car frames have them but maybe the placement/size/shape is important.

 

[cwm]

If you want more strength to the frame continue the tongue as a backbone down the middle and under the cross members.

Someone mentioned pulling the skin off the foam. That sounds like the wrong kind of foam. Foam with a skin may be beadboard, expanded polystyrene. Beadboard because of it's structure can actually hold some moisture.

Extruded polystyrene is a better choice. It also has a higher R-value. The two most popular brands are Dow Chemical's Styrofoam brand , blue color or Owen Corning Formular brand, pink color.

The building center/lumber yard carries the 25 psi version. Insulation distributors carry a high load version in 40 or 60 psi.

 

[Strider]

Good advice!
Thank you!

 

[Capt Eddie]

You are correct. But both brands have a thin plastic coating on them. You can put this coating off to get better adhesion to the insulation itself. The plastic film seals the pores of the insulation. By pulling it off you allow the glue to adhere to the pores of the foam itself.

Strider; What do you see as the advantage of using C Channel for the tongue but not for the frame? The labor of cutting in the holes would be a waste of time and money. Use the right material that does not need human manipulations. The holes will fill with dirt and there is your rust. The drawn plans that you have shown would be fine. But you may need to add spacers to get the frame to the correct level of the main tow vehicle. I would design so that the trailer sits at the same level as the truck body. Then you will know that if the truck made the obstacle the trailer can make it. if the back corner is 25 inches off the ground, make the trailer body the same thing. You would do this with spacers above the axle.

 

[Strider]

Strider; What do you see as the advantage of using C Channel for the tongue but not for the frame? The labor of cutting in the holes would be a waste of time and money. Use the right material that does not need human manipulations. The holes will fill with dirt and there is your rust. The drawn plans that you have shown would be fine. But you may need to add spacers to get the frame to the correct level of the main tow vehicle. I would design so that the trailer sits at the same level as the truck body. Then you will know that if the truck made the obstacle the trailer can make it. if the back corner is 25 inches off the ground, make the trailer body the same thing. You would do this with spacers above the axle.

It just seems that tube is stronger than c especially in off road use. The Aussies build really great trailers and they use tube. But then, like you said, they have those things hot dip galvanized so they don't have to worry about the rust issues like home builders do. I had planned on tubing with either the holes as described or drilling a hole after welding, pouring in good paint (I even thought of used gear oil which seems to stick to everything forever) and then plugging the hole with silicone or a bolt with the threads sealed too. Also C seems a lot more difficult to put things on.
But I am still listening. Every time I think I found the answer another good point is made and my brain scrambles all over again. :xxrotflma

 

[Capt Eddie]

Please do not drill or cut holes in the frame. But Paint, oil will not keep water buildup out.. Then it freezes and burst the tubing. If you paint it, leave some 1/2" weep hole. I made a pipe rack out of 2 x 2 x1/4" It got water in it and bust the side of the tube out. 1/4"!!!!!!. I would not believe it if I had not done it to myself. Have you thought how to run the wiring? That could be the reason for weep holes. Be sure to you rubber grommets.

 

[cwm]

"You are correct. But both brands have a thin plastic coating on them. You can put this coating off to get better adhesion to the insulation itself. The plastic film seals the pores of the insulation. By pulling it off you allow the glue to adhere to the pores of the foam itself."

Capt Eddie

Could you explain exactly how to remove this coating from extruded polystyrene? I am very familiar with the Styrofoam Brand from Dow Chemical and I have never seen a coating on it. The Styrofoam Brand has the blue color completely through it because that is Dow's marketing color for this product.

I even have some white and some black pieces and there is not a coating. There are no pores in extruded polystyrene. I think that you are confusing it with expanded polystyrene which has a pebble like structure (pores). This comes from how the polystyrene pellets expand and stick to each other in the manufacturing process.

 

[spressomon]

Just an FYI/FWIW: My '99 Land Cruiser's frame has numerous, from the factory holes, in its rectangular tube style frame...been through plenty of water crossings without any rust issues. The same applies to the Kimberley Kamper frame. I can not say what interior coating, if any, Toyota might use to coat the interior of their frames. And the KK frames are double hot dipped galvanized.

Whether you opt to use "C" channel or tube you will still need to think about how to mitigate abrasive spray from the tow vehicle. The galvanized dipped frame and bedliner coated fiberglass nose box on the KK were impervious to tow vehicle's gravel spray; whereas the powder coated frame (and side boxes) on my AT Horizon was left with the equivalent of being aggressively sand blasted after all the gravel roads it was pulled over.

 

[Capt Eddie]

Could you explain exactly how to remove this coating from extruded polystyrene? I am very familiar with the Styrofoam Brand from Dow Chemical and I have never seen a coating on it. The Styrofoam Brand has the blue color completely through it because that is Dow's marketing color for this product.

I even have some white and some black pieces and there is not a coating. There are no pores in extruded polystyrene. I think that you are confusing it with expanded polystyrene which has a pebble like structure (pores). This comes from how the polystyrene pellets expand and stick to each other in the manufacturing process.[/QUOTE]

If you take the pink insulation and cut a line on one side with a razor knife. There will be a thin plastic coating on the other side that most be cut to separate the two pieces. Instead of cutting the plastic. Peel it off one of your pieces of foam. You will see that the piece without the plastic will broke in your hands. While if you try to break the piece with plastic you almost can not do it. Take a razor knife and cut under one end of the insulation then peel the plastic off. All of this information is really useless to most people. Most people will encapsulate the insulation in something. This technique would only be necessary if you were bonding the foam to something and needed max strength like a wall. I would have no problem building the whole trailer out of luan and foam. Then coat the luan with gym floor polyurethane.

 

[thethePete]

I grew up building trailers with my father in his fabrication shop. His trailers were licenced and certified to be legally sold and used on Canadian and US roadways complete with VIN.

We never built trailers with channel. Not a single piece of it. Channel is used by manufacturers to save money and cut corners. It is impossible for C-channel to be as strong as square tubing when all other things are equal. Full stop.

For our trailers, up to a 16' tandem axle utility trailer would get 2x3x.250 tubing for the main perimiter frame, and 1x1x.100 (known as 100 wall tubing) for our crossers on 12"-24" spreads, depending on application. Our trailers were not over weight but extrordinarily overbuilt for their target market. My dad is still using the one he built for himself 12+ years ago, it sees 100km+ of gravel road every single weekend, and apart from a few tremclad touch ups, it's as good as it was the day he built it. We did not coat the interior of our tubing and we are in the heart of the Canadian "rust belt".

C-channel is a compromise, and we never did like using it because channels create ledges for dirt and water to sit and rust, and it is not as structurally sound as tubing. We ended up closing up shop because people couldn't appreciate the value of a quality built trailer and we were undercut by a local trailer shop who sells mass produced trailers, made using angle and c-channel. My father could not source his materials for as cheap as they were selling their trailers, and he was unwilling to compromise his quality of work by resorting to c-channel and angle like the mass produced trailers. He still makes the occasional one-off, but he's gone back to construction fabrication because people are unwilling to pay for quality when they can get "the same thing" for $500 less. It's a shame.

 

[Capt Eddie]

thethepete: I am sorry but I cam not agree with most of the statements that you have made. Channel is stronger pound for pound then tubing is in the right structural application. 1 x 1 x .100 has no structural strength to be used in a crosser application. Anyone can take a 100 wall tubing, support it at both ends of an 8 foot span . It will bend It will not support a 200 lb man without bending in the middle. But a 2 inch C channel has the same weight but will not bend. Try it out. The ledges of the channel have a slope to them. yes water and dirt may get on it, but will come off driving down the road. Where tubing will rust from the inside. And if you do weld the end of a tube up solid. Condensation will freeze and bust the tube. Channel is a solid piece of metal. Any voids in the metal are visible. Tubing has seams that in most cases are thinner then the main structure. The wall thickness of tubing is 1/2 the thickness of channel of the same weight. This allows screws and welds to hold. Try this for your self. Take a piece of 2 x 2 x 1/8 tubing. Cut it in half. This will give you a 2 x 1 x 1/8 C channel. A 2 x 1 channel of the same weight will have a 1/4 wall thickness. Would you rather drill, screw and weld a piece of metal 1/8 thick or 1/4 inch thick? If you make a good high quality product of any nature. people will beat a path to your door. I would rather build one good trailer with a good profit margin then build 5 cheap trailers.

 

[762X39]

I find this topic to be interesting and controversial. Light duty trucks do use hydro-formed high strength steel boxed frames but all the medium to heavy duty trucks (including my little 1 1/2 ton Unimog) seem to use C channel that is bolted or riveted together. What am I missing ( are there any metallurgical/structural engineers reading this that can tell me the answer?). I figure there must be a reason why C channel is used in heavy duty applications. I also wonder why so few people galvanize their projects. There are 2 galvanizing plants within 45 minutes of my house. I have used the closer plant to galvanize a rack I built. There is a minimum charge and it is expensive but never having to sandblast and repaint a project is worth the price of admission.

 

[Strider]

Thank you all for all the input. Very educational information. I am still on the fence about tube vs c. Both sides are making some very good points.
I have a 110 volt Lincoln MIG welder; a Handymig. This may be the basis of my decision as I don't think it is good for welding 1/4" steel. I welded a roof rack, bullbar, rear bumper & tire/jerry can rack for my Jeep using a cheapie wire welder a few years ago and this one is better but again I don't know about 1/4". Also tubing just seems easier to bolt &weld to.

Of course, an alternative is to have a local trailer builder make up the frame and I can the do the body box and finally put on the Timbren axles.

 

[tgreening]

I find this topic to be interesting and controversial. Light duty trucks do use hydro-formed high strength steel boxed frames but all the medium to heavy duty trucks (including my little 1 1/2 ton Unimog) seem to use C channel that is bolted or riveted together. What am I missing ( are there any metallurgical/structural engineers reading this that can tell me the answer?). I figure there must be a reason why C channel is used in heavy duty applications. I also wonder why so few people galvanize their projects. There are 2 galvanizing plants within 45 minutes of my house. I have used the closer plant to galvanize a rack I built. There is a minimum charge and it is expensive but never having to sandblast and repaint a project is worth the price of admission.

There is more than one type of C-channel and I think the they are being used here in a confusing way. Capt Eddie is talking about structural C. I dont recall ever seeing any truck builders using it, at least not recently. They use open box channel, the material of which has a uniform thickness all the way around. The reason they use it is it makes it easy for upfitters to add stuff like flatbeds, dump bodies, utility boxes, etc. There is a builders code that the manufacturers adhere to so upfitters have a consistent and uniform platform to build off of.

Another reason is open box channel doesnt mind twisting some, which comes in handy when you're taking your truck off road across uneven terrain. Thats why your pickup truck bed isnt attached directly to the cab.

Structural C otoh doesnt really like twisting, which is one of the reasons it is recommened that it is bolted/welded up against something when used. Like another piece of C to form an I-beam. Another reason it's recommended to back it with something is you cant center a load on top of it.

For what the OP is doing I believe he is much better off using the box tubing and being done with it. Unless he is pulling his trailer through the ocean on a regular basis rust isnt going to be an issue. I find the notion of burst tubing due to frozen condensation...unlikely, and strength of weld a non-issue as long as the welder is competent. Welded properly you will destroy the surrounding base material before the weld fails. And yes, I'll take 4 walls of welded .120 2x2 over the .250 C-channel being proposed.

I have a bit of experience when it comes to joining metal. In my line of work .0625 mig is used for detail work. Real welding is done with .120 wire or bigger. A 1/4" stick electrode is tiny. On the last job that I was personally involved in I burned up more electrode than everybody on this website has, combined, for life. There's a chance I'm wrong, but unless they can add up all their usage and exceed 30,000lbs, I win. And compared to most of my welders I'm a light weight.