Trailer frame and welding angle

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I am building a medium duty trailer frame to make a mobile food cart on (about 2500 lbs.).  Most trailers I see are butt welded, leaving some of the tube steel open which can rust.  I wanted to cut the metal at 45's and weld them together, closing and sealing the tube steel from oxygen and water to prevent rust inside the tube steel frame.  Will the welds at 45's be as strong as flat butt welds. Good idea or not.
Reply:Either joint will work.  As for strength, if you weld all the way around the weld will not be your weak point. As for strength of the weld, technically speaking, if you cut the weld (think big band saw) the 45 cut will have more surface area and thus be stronger.Fitup is tougher (more work) and welding prep more work and finally welding slightly more difficult.  Risk from distorting the frame is higher.Last thing, the cost or rectangular tube is significantly higher than C-channel or angle iron.  So you are going to spend a lot more on materials.  Tubing is much better in torsional stiffness, but pound for pound, a tall C-channel will carry more load.Its all trade-offs.  However, I agree about your assessment that a sealed tube will never rust from the inside.   I think you could get almost the same anti-rust by using C-channel and carefully prepping and painting the trailer.  Again, trade-offs.Con Fuse!Miller Dynasty 350Millermatic 350P-Spoolmatic 30AMiller Multimatic 200Hypertherm PowerMax 1000G3Miller Maxstar 200DX
Reply:I would first suggest searching other trailer threads. As they all say what I'm about to. "if you have to ask, you shouldn't be building a trailer."that being said, closing the tube vs leaving it open has two sides of the fence. so prefer the open because when water gets in, it can then get out. others prefer sealed because it reduces the chance of water getting in, though it's hard to actually seal the tube properly. Most prefer to stay away from tube all together and just go with channel and angle.As for the Butt weld vs angle, you'll have to wait for others to chime in.There are no problems. There are only solutions. It's your duty to determine the right one.Hobart Handler 210Airco 225 Amp MSM Stinger
Reply:If you don't know about the joints then I would think about some smaller projects and maybe build the trailer in a year or two. The liability of building a trailer  and having some thing fail because you are inexperienced would be huge, let alone that you could kill some one. Not trying to be mean here but practical.
Reply:somewhat relevant .... somewhat not, perhaps.  My wife's uncle built a hunting trailer in this fassion.  he used tube steel as a perimiter frame, and then welded in a bung for a schrader valve, and a quick detach air chuck.before hunting, he fills the frame up with compressed air and brings along an air hose for the trip.  if he has a flat (more like 'when'), he hooks his hose up to his portable air tank (trailer frame) and fills it up.apparently he is an alright welder ... cauz it dont leak.just thought i'd throw it out there, perhaps a not to often thought about advantage to a tube frame.
Reply:I would be more scared of a pressure vessel than any trailer. ...see Accidents in Pressure Vessels: Hazard Awareness.About the question of joint configuration verses strength, it depends. Sound welding of either joint will suffice. Either joint will fail if not up to snuff. I usually get pinned between making it "look good" or making it "work good". If I can do both of those things, I'm happy. Last edited by tanglediver; 01-26-2012 at 12:41 AM.City of L.A. Structural; Manual & Semi-Automatic;"Surely there is a mine for silver, and a place where gold is refined. Iron is taken from the earth, and copper is smelted from ore."Job 28:1,2Lincoln, Miller, Victor & ISV BibleDanny
Reply:Originally Posted by tanglediverI would be more scared of a pressure vessel than any trailer. ...see Accidents in Pressure Vessels: Hazard Awareness.About the question of joint configuration verses strength, it depends. Sound welding of either joint will suffice. Either joint will fail if not up to snuff. I usually get pinned between making it "look good" or making it "work good". If I can do both of those things, I'm happy.
Reply:Meborder, It's half the project, and half the person. Some projects are just beyond the scope of the person doing them. there are two sayings that go hand in hand if you ask me. Better safe than sorry, and if you have to ask, you shouldn't be doing it. If you've got to go to a web forrum to verify a theory, than you don't have the right people around you to insure that you're doing the project right. If you did, you wouldn't have to go online to find the answers. Also, you should check out the safety forrum. there are several threads in regards to preasure vessels. that have catistrophic failures with even as low as 40 PSI.  120 PSI is a lot of preasure. If the weld isn't up to snuff it will fail. and more than likely it will fail when someone is close by.  With the potential for death, it's not worth the risk unless you know exactly what you're doing.There are no problems. There are only solutions. It's your duty to determine the right one.Hobart Handler 210Airco 225 Amp MSM Stinger
Reply:With pressure vessel safety, its not so much the pressure your dealing with but has more to do with the surface area and the volume of the vessel. A small vessel under a lot of pressure can be a lot safer than a large vessel under a little pressure. Just do a little math and you can see what I meanVessel with 100sq inches of inside surface area under 100psi, potential of 10,000lbs of energy in thereVessel with surface are of 1000sq inches under 10psi, same 10,000lbs of energy containedJust look at what a gas bottle can do when the valve gets knocked off (2-3000psi pushing a 1-200lb cylinder with enough force to go through block walls)
Reply:Now going back to the trailer question, a stronger joint that is easier to fit up and weld would be a coped joint, basically you cut 3 sides of your tube to but into the intersecting tube but leave the 4th side long enough to act as a cap on the end of the intersecting tube. This ties the tubes together over a larger area and in more than one plane and also seals the tube to water problems.
Reply:Either set up will work, but just remember that even though its a sealed tube you will stilll build up condensation inside so you will need a weep hole for that condensation to drain.UA Local 598
Reply:Originally Posted by ironmangqNow going back to the trailer question, a stronger joint that is easier to fit up and weld would be a coped joint, basically you cut 3 sides of your tube to but into the intersecting tube but leave the 4th side long enough to act as a cap on the end of the intersecting tube. This ties the tubes together over a larger area and in more than one plane and also seals the tube to water problems.
Reply:If all you want to do is seal it butt welds are fine and cut square plugs to slip in the open ends.x2 on the weep hole.Millermatic 252millermatic 175miller 300 Thunderboltlincoln ranger 250smith torcheslots of bfh'sIf it dont fit get a bigger hammer
Reply:Just for closing tubes, you can try painting an inch or so on the inner side and then put a plastic cap in it if you dont want to weld a plate at the end.Like these ones:http://www.stockcap.com/prod_detail.asp?id=168&cat=13You can get them in rectangular shapes too (or pipes).Not the most proper solution, but it will hold a lot of water splatting in.
Reply:Don't know what region you are in but if you weld it and it takes water then freezes you will be in for a whole other problem, ice can do some serious damage when it is restrained in a tube. Is tough for a newby to get a total seal, and it still won't prevent condensate. But anybody who ever owned a mid 80's toyota truck can tell you about the horrors of a tube frame out in the elements. Most any of the structural shapes are good if you go heavy enough, but tube will cost you more and channel and angle will get it done. A good powder coat will do wonders and you can spray it off with the pressure washer to keep it looking good.  Did you say food trailer? Get out your wallet and go with stainless or aluminum, no paint required. LOL  Good luck with the project."Si Vis Pacem Para Bellum"Lincoln Idealarc 250 AC/DCMillermatic 251   Syncrowave 300   30A spoolgunLincoln MP210Hypertherm 45(2) LN 25(2) Lincoln Weldanpower 225 CV(4) SA200   1 short hood    SA250    SAM 400