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Best way to sister C channel to to Square Tubing

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  • #16
    I'm not even going to comment on how crazy I think the whole idea is.

    Sistering a second C channel to the first would be the most economical way to approach the problem, however what you'd create he is a nearly guaranteed entrapmant of moisture/water and the resultant rust which would quickly destroy the trailer.

    Anyone who suggests welding a square tube to the web to gain strength must have never taken a structural course.
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    • #17
      Originally posted by SundownIII View Post
      what you'd create he is a nearly guaranteed entrapmant of moisture/water and the resultant rust which would quickly destroy the trailer.
      Could always use caulking to fill in between the stitch welds.
      Caution!
      These are "my" views based only on “my” experiences in “my” little bitty world.

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      • #18
        He11 Yea!

        5200 (marine sealant) will hold nearly anything. Almost as useful as 100 MPH (duct) tape.

        Now why didn't I think of that.
        Syncrowave 250 DX Tigrunner
        Dynasty 200 DX
        Miller XMT 304 w/714D Feeder & Optima Control
        Miller MM 251 w/Q300 & 30A SG
        Hobart HH187
        Dialarc 250 AC/DC
        Hypertherm PM 600 & 1250
        Wilton 7"x12" bandsaw
        PC Dry Cut Saw, Dewalt Chop Saw
        Milwaukee 8" Metal Cut Saw, Milwaukee Portaband.
        Thermco and Smith (2) Gas Mixers
        More grinders than hands

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        • #19
          Well, Sundown III, Sonora keeps telling us he's from Mexico, he might know more about beefing up camp trailers than anybody else here .... Not too many other reasons I can think of, to carry double the weight .....
          Obviously, I'm just a hack-artist, you shouldn't be listening to anything I say .....

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          • #20
            Originally posted by kraythe View Post
            So it carries more load of course. I want to put a bunch of things on it and I dont want to be restricted to the old capacity.
            Just curious will your axles handle all these mods, your planning on making? Just wondering hate to build an elephant on a mouses back.

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            • #21
              Originally posted by stick man View Post
              Just curious will your axles handle all these mods, your planning on making? Just wondering hate to build an elephant on a mouses back.
              The axles will be swapped out for new along with all of the springs and other suspension gear. That was already in the plan.

              I have noticed there are some great helpful people here and some that ... aren't. I think I will ignore the latter of the two.

              I thought about closing the c channel but I dont know if that would be good enough. I have a picture of a frame that is VERY MUCH like the one I am considering.

              Click image for larger version

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              The C channel is 10 gauge and I think the height is 6 inches. This picture is from a similar trailer that the person beefed up by welding rectangular tubing to the long support members but then he was trying to carry a car in the trailer and i am not so ambitious as that. I just want to carry the furnishings of a luxury travel trailer.

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              • #22
                I wouldn't want to be stopping & stopping my intended reinforcement at every one of those wings or cross memebers depending on which way those purlins are placed on there. That sets up a whole new set of potential problems there.

                On the trailer you plan on beefing up take a long serious look at the existing welds where those cold rolled C's meet the C purlins and other key points. They were likely done under a low payed production environment and I've seen plenty that were pretty scarry.

                One other consideration is the type of coating that's on there. Some of it is some pretty rugged stuff and put on wet enough to flow down into any bad welds and make it nearly impossible to get off or weld through or over to fix up any bad welds. Any welds that look good peck around to make sure it's not just painted over slag to get a trend on the overall quality. Might be fine, might not.

                I've re-done two of what you would consider very small trailers. I'll never do another.

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                • #23
                  kraythe,

                  After seeing the questions you've asked here, and going back and reading some of your previous postings, I seriously doubt your ability to pull off the reinforcement of the trailer successfully.

                  The reinforcement you're talking about (to achieve a 175% strength increase???) can, in fact, be much more difficult to accomplish than starting from scratch and building a new trailer. Adding strength to one component, without considering the impact elsewhere, will almost surely cause a failure in a component which was not similarly reinforced. By the time all these factors are taken into account, you've spent more time/money than a new frame would have cost.

                  Going back to your original question, simply adding/welding a box tube to the flat of the C Channel makes absolutely no sense as, I think, another poster has already pointed out.

                  Not trying to "pick on you", just reemphasizing that this is a BAD IDEA.
                  Syncrowave 250 DX Tigrunner
                  Dynasty 200 DX
                  Miller XMT 304 w/714D Feeder & Optima Control
                  Miller MM 251 w/Q300 & 30A SG
                  Hobart HH187
                  Dialarc 250 AC/DC
                  Hypertherm PM 600 & 1250
                  Wilton 7"x12" bandsaw
                  PC Dry Cut Saw, Dewalt Chop Saw
                  Milwaukee 8" Metal Cut Saw, Milwaukee Portaband.
                  Thermco and Smith (2) Gas Mixers
                  More grinders than hands

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                  • #24
                    Perhaps I was unclear with the numbers. I wasnt looking for a 175% increase but rather a resulting strength equal to 175% of the original or a 75% total increase. I have seen it pulled off with a car hauler and the trailer is still in operation.

                    As for the coatings, I am not worried about that as the whole thing will be sandblasted prior to any welding.

                    When it comes to the weld quality, from what I have seen this manufacturer kew their stuff. I haven seen any shorn welds and the original trailer was in service for years before being serviced. This trailer was built in 1949 so most the welds would have been done by hand and either stick or torched. They look solid in other frames I have looked at.

                    As to reinforcement, I could stitch weld closures to the c channels to the purlins and then on the other side and so on down he frame. It would certainly help with the strength but not cutting the reinforcement at each cross member isnt ideal. The fellow who did the car trailer welded 2" x 6" x 1/4" wall tubing under the main beamc and it seems he notched the rectangular tube. http://www.cardomain.com/ride/340096/5

                    I dont need THAT much reinforcement as his trailer was noticeably smaller than the one I am considering and I am not looking to support a car on the frame.

                    Now I could fabricate an all new frame from larger stock to begin with but that would be a much more expensive and time consuming proposition and the old frame would be wasted and that would be a waste. If all else fails I will go that route.

                    If I could figure out how to compute the strength of this thing then I would be better off but I am not a mechanical engineer and I dont have access to compute dynamic load. What I would need to know is the carrying capacity GVRW of the 10 gauge C channel members over the length of the trailer frame with an even load. If it is high enough and the axles are the weak point then life is grand and no reinforcement is needed. If not then I need to really think about what to do.

                    And no, I am not going to abandon the project for one snag in the yarn.

                    -- Robert

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                    • #25
                      Originally posted by SundownIII View Post
                      kraythe,
                      Going back to your original question, simply adding/welding a box tube to the flat of the C Channel makes absolutely no sense as, I think, another poster has already pointed out.

                      Not trying to "pick on you", just reemphasizing that this is a BAD IDEA.
                      So he and you say. I would like to know the answer to "Why?" and "Why did it work for the other guy?" Opinion is all well and good but I am a facts sort of guy.

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                      • #26
                        Maybe this will help on the question of 'why'

                        Adding more material near the neutral axis doesn't gain you anything. You'd rather add material away from the neutral axis.
                        For example, compare an I-beam to a solid rod with the same weight/foot. You have the same amount of material in both pieces, but the I-beam is going to be much harder to bend. Having the material spread out gives it more leverage to resist bending.

                        You would be better by adding the square tubing across the open side of the channel. This puts the web of the channel farther away from the neutral axis. This also creates a closed cross section. Using the same material a closed cross section will be much more resistant to twisting than an open one. Try twisting a pipe, then cut a slit down the pipe lengthwise and try twisting it again. Small drain holes won't change the strength of the closed section much.

                        I agree with most of the others. This trailer's design does not make modification worthwhile. You could spend lots of time and filler metal trying to modify this trailer and still not get it right. Or you could spend much less time, a little more on new material, and have a much better result.

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                        • #27
                          OK Fair enough. The question would be then what would be the correct sizing for rectangular tube if I did the whole trailer? What factor does shape contribute to dynamic loading and how much increase do i get going from C channel to rectangular tube and what sizing should I use to carry the load.

                          If I could I would weld it out of aluminum as well to save on weight and reduce galvanic corrosion possiblities with the shell of the camper but perhaps that would require so much more material that I would gain little. One nice thing about re-engineering the trailer frame is that I would have an easier time locating the four tanks I need in the RV. One 40 gallon fresh water, one 40 gallon grey water, one 40 gallon black water and one aluminum diesel fuel tank.

                          At times I wish I had gotten a mechanical engineering degree.

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                          • #28
                            Why not look into a used flatbed trailer with the capacities you need, then modify it? Don’t know about your area but I’ve seen a dramatic drop in price of used flatbed trailers over the last couple years.
                            Caution!
                            These are "my" views based only on “my” experiences in “my” little bitty world.

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                            • #29
                              Originally posted by Sonora Iron View Post
                              Why not look into a used flatbed trailer with the capacities you need, then modify it? Don’t know about your area but I’ve seen a dramatic drop in price of used flatbed trailers over the last couple years.
                              I thought of that but then figured I would have to find the PERFECT fit flatbed to make it work and for that kind of cash I could put together a brand new frame.

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                              • #30
                                Originally posted by kraythe View Post
                                At times I wish I had gotten a mechanical engineering degree.
                                Sounds like you'll need a ME to of the redesign/rebuilt of a complete RV. Each little piece is going to be just as complicated at determining how to beef-up the frame (how much, where, what shape).

                                How much wind load do you expect? Say 100MPH (60mph cruise + 40mph head wind). How much actual force does this apply to the RV? Without fluid modeling computer simulations how do you figure this out? Build a test rig with a sheet of plywood and some bathroom scales??? Or do you just really overbuild it to be safe and end up with a 10000lbs RV trailer?

                                Where do you mount your tanks? How do you compensate for the weight shift when the fresh water tank empties and the black water tank fills? Does the trailer lift the back of your truck when this happens? How do you mount your tanks to avoid them breaking free when you hit that 6" deep pothole? How do you avoid the sloshing in the tanks making you weave all over the road? Do you use baffles? How do you baffle the black water tank without getting poo stuck in places you have to clean out? Nobody likes cleaning poo!

                                If you want a homebuilt RV, take a look at old school buses. These have all the structural work done for you. It has a chassis that will carry the entire football team (200lbs * 4 per row * number of rows. It really adds up!). You can gut the seats and build your own interior. Tanks are still a problem, but I think you'd be way ahead. I've seen running buses around $1000.

                                Either way you have your work cut out!

                                You might want to get a copy of "Design of Welding Structures" from Lincoln. https://ssl.lincolnelectric.com/linc...sp?prodnum=DWS This has some of the information you're looking for: calculating beam loading, etc, etc. It's $22 last time I looked. Money well spent. Someone else might know of a better book.

                                Dynasty200DX w/coolmate1
                                MM210
                                MM Vintage
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                                Victor O/A, Smith AW1A
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                                Jancy USA101
                                9" South Bend
                                AEAD-200LE

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