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Aluminum trailer - but too much flex

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  • Aluminum trailer - but too much flex

    I'm building a big but lightweight flat deck trailer. I wanted something that I'd be able to say put a pontoon boat or aluminum dock on but also be able to pick up materials with. Basically long stuff but not heavy. When I look at boat trailers they are built so light that I thought mine wasn't going to be an issue. But it has waaay to much flex to it. Its not that the beams are sagging or deflecting, its that the whole things twists back and forth when I push down on a corner. I thought when I bolted down the deck it would help a lot but it's made it worse. The main beams are 4" x 2" x 3/16 on the web and 1/4" on the flange, 6061 t6 aluminum. The cross members are 3" x 1 1/2" channel as thickness. I wanted to avoid any welding on the beams as that would take the temper out and weaken them. So I thought I was being smart by simply bolting the cross member to the top of the beams. This also raised up the deck enough to clear the wheels. Now that I think about it, I'm thinking this is why its flexing like a bast*rd. I'm wondering what the best solution would be without using a ton more metal.

    A few things I can think of:
    a) I could cut pieces of 3" channel and bolt them on top of the beams in between cross members. Then probably weld those pieces to the cross members at the ends. While this would probably increase the load capacity of the trailer I don't think its the solution to the flex.

    b) The easiest method may be to bolt some angle or channel cross members to the bottom of the beams underneath the upper cross members. I could also maybe cut some short pieces of square tube to go between the upper and lower cross members to basically turn it into a truss. Maybe this would be the best option but probably not the cheapest. I do have some 2"x1" channel that was pretty cheap and may do the trick.

    c) A bit more work but would use less metal would be to build some sort of bracket that bolts to the bottom of the beams and slopes up at an angle and bolts to the cross members. As I type this I'm kind of leaning towards trying the 2x1 channel in method b.

    Thoughts?

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    www.silvercreekwelding.com

    Miller Trailblazer 325 efi
    Miller extreme 12vs
    Thermal arc 186 ac/dc
    Lincoln power wave 455m/stt with 10m dual feeder

  • #2
    Needs another axle.......and a deck would help..........like your shop and backyard!

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    • #3
      Thanks. Another axle might help slightly but I don't think its the cure. I may add a second axle in the future. Also like I said the deck is bolted on now but the weight actually made it worse.
      www.silvercreekwelding.com

      Miller Trailblazer 325 efi
      Miller extreme 12vs
      Thermal arc 186 ac/dc
      Lincoln power wave 455m/stt with 10m dual feeder

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      • #4
        I think a second axle would make a substantial difference. With as long as that trailer is you really need a second axle. I'm not a trailer expert, but that trailer axle looks a bit far back to what I'm used to seeing. And this is not a boat trailer, right?

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        • #5
          Love the shop and the background view. Wow...Bob
          Bob Wright

          Spool Gun conversion. How To Do It. Below.
          http://www.millerwelds.com/resources...php?albumid=48

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          • #6
            No kidding...lucky dog.

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            • #7
              Originally posted by ryanjones2150 View Post
              I think a second axle would make a substantial difference. With as long as that trailer is you really need a second axle. I'm not a trailer expert, but that trailer axle looks a bit far back to what I'm used to seeing. And this is not a boat trailer, right?
              Your right it is a bit far back. My reasoning was that if I was too have a pontoon boat on the back the engine would put more weight on the back. And when I want to upgrade in the future with another axle it would end up being closer to the ideal spot.

              Still I dont think thats what will fix the flex. If I took a heavier 20' flat deck and stripped it down to one axle I bet it wouldn't have that flex. It kind of reminds me of when I built my shop (which was engineered by the way) and I had put the steel up without anything else attached. It was super wobbly and I thought wtf, how is this thing going to work. But once I put the walls up and attached the rafters to the top of the beam it become 10x more stiff. Did it increase the load capacity of the beam? No, but it sure made it a lot stiffer. I'll bolt some channel cross members to the bottom today and see what that does but Im still hoping someone with a bit more structural engineering knowledge then myself will chime in.
              www.silvercreekwelding.com

              Miller Trailblazer 325 efi
              Miller extreme 12vs
              Thermal arc 186 ac/dc
              Lincoln power wave 455m/stt with 10m dual feeder

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              • #8
                Originally posted by ryanjones2150 View Post
                No kidding...lucky dog.
                Lol. Its a beautiful place but landing a well paying job around here is not easy. Which I why I decided to go on my own. It's been pretty stressful and if I dont get some more jobs soon I don't know what the heck I'll do. Luckily I just lined up a job to build some dock pontoons for a guy and building more of those might end up being a good gig. I think/hoping its going to be a busy spring and that its just been a matter of getting my name out there. All the other welding shops around here seem to really busy.
                www.silvercreekwelding.com

                Miller Trailblazer 325 efi
                Miller extreme 12vs
                Thermal arc 186 ac/dc
                Lincoln power wave 455m/stt with 10m dual feeder

                Comment


                • #9
                  Add a second axle. We add forklift baskets on the back of 45' semi trailers. That adds 10,000 lbs. in a place it wasn't designed for. Our first trailer had tandem axles all the way in the rear with no spread. That trailer always had a bad twist to it. After about 8 or 9 years of daily use and several dozen sub frame crack repairs the front corners of the trailer would dip so far it would hit the tires of the tractor pulling it. We were to busy to work on it (and I didn't want to move the axles myself) so we sent it out to a trailer repair place and they did whats called a California spread. They moved the front axle forward to get like 8' or 10' axle to axle spread. That pretty much took care of the twist.

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                  • #10
                    While I'm a little uncertain, I assume diagonal twisting is your concern? If you held it, each side in your hand and gave it a twist, what would a stiffener down the middle do to stiffen it up? It would result in a firm core in the middle resisting the twist?

                    Imagine stress flow lines, how pushing here moves over there... Wouldn't stiffening means you obstruct them? I think it needs a back bone down the middle because the perimeter tubes are too far apart to provide the stiffening to avoid twisting flex. My guess anyways?

                    For example, look at a highway trailer. The supporting frame rails are not on the outer edges but rather tucked inside. Then the bed/deck surface does the work of supporting what's on top for surface area. Again, I'm no engineer just a guesser?

                    I'm not sure of the bolting over the welding? Maybe we can have coffee one day and discuss it further? Looking good though. Nice to see someone working hard, as lately, I've been hardly working?



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                    • #11
                      Originally posted by Noel View Post
                      While I'm a little uncertain, I assume diagonal twisting is your concern? If you held it, each side in your hand and gave it a twist, what would a stiffener down the middle do to stiffen it up? It would result in a firm core in the middle resisting the twist?

                      Imagine stress flow lines, how pushing here moves over there... Wouldn't stiffening means you obstruct them? I think it needs a back bone down the middle because the perimeter tubes are too far apart to provide the stiffening to avoid twisting flex. My guess anyways
                      Ya its the diagnol twisting that concerns me and the stresses that its going to put on the frame over time possibly causing cracks like grandad said he got on his trailer. So your thinking a second frame rail down the middle would help resist the twisting?

                      The general consensus seems to be to add a 2nd axle and like I said I was planning to possibly add a 2nd one in the future if I wanted to increase the capacity. I was hoping to avoid the cost for now but I agree it would probably help a fair bit. Im gonna play with it a bit today and see what I can do with some of this channel I have.
                      www.silvercreekwelding.com

                      Miller Trailblazer 325 efi
                      Miller extreme 12vs
                      Thermal arc 186 ac/dc
                      Lincoln power wave 455m/stt with 10m dual feeder

                      Comment


                      • #12
                        I think the flex is inherent due to the size of the material being used along with the span in both width and length..............that and I would weld it all vs bolting it together which is nothing more than a clamp in your case.

                        I have a 40' goose neck aluminum enclosed race trailer............no chassis pur-se but the floor / frame is made out of a extruded channel.......flat on one side ( top / floor) and the bottom resembles a ( ship channel) with a 3rd leg in the middle.......these measure 12" wide x 2" tall and are cut to whatever width you need ....... the pieces also have a grove on both sides that allows the parts to be assembled or slid together across the trailer width and then stitch welded on the bottom and ends only.............the axles ( 2 ) are attached to a large steel angle and then Huck Riveted to the aluminum chassis , the goose neck portion is the only thing that is steel and welded together.......extremely light and strong......and a pleasure to pull as compared to it's counterparts that are all metal with wood interiors....

                        Comment


                        • #13
                          Originally posted by Willvis View Post

                          Ya its the diagnol twisting that concerns me and the stresses that its going to put on the frame over time possibly causing cracks like grandad said he got on his trailer. So your thinking a second frame rail down the middle would help resist the twisting?

                          The general consensus seems to be to add a 2nd axle and like I said I was planning to possibly add a 2nd one in the future if I wanted to increase the capacity. I was hoping to avoid the cost for now but I agree it would probably help a fair bit. Im gonna play with it a bit today and see what I can do with some of this channel I have.
                          Tell you one way to find out, cut a cereal box side panel and tape a stiffener down the middle and see how it twists after doing so? I'm not sold on adding another axle although it will, support a greater load in doing so down the length. The extra axle added, while creating a small stiffer "box" will resist some twist but I don't think it's your solution because the axles still will twist? I think the long length rail are too wide apart to resist diagonal twist effectively? Is a back bone the answer? The cereal box may tell you? I'm doubting you want to take it apart to redesign at this point so I'm expecting an add on is in order to offer a degree of resistance to diagonal stress is a solution? Two would probable be better but again, card board and tape will be a way to find out and won't cost much to do so. Kids will probably enjoy it as well?

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                          • #14
                            Originally posted by tarry99 View Post
                            I think the flex is inherent due to the size of the material being used along with the span in both width and length..............that and I would weld it all vs bolting it together which is nothing more than a clamp in your case.

                            I have a 40' goose neck aluminum enclosed race trailer............no chassis pur-se but the floor / frame is made out of a extruded channel.......flat on one side ( top / floor) and the bottom resembles a ( ship channel) with a 3rd leg in the middle.......these measure 12" wide x 2" tall and are cut to whatever width you need ....... the pieces also have a grove on both sides that allows the parts to be assembled or slid together across the trailer width and then stitch welded on the bottom and ends only.............the axles ( 2 ) are attached to a large steel angle and then Huck Riveted to the aluminum chassis , the goose neck portion is the only thing that is steel and welded together.......extremely light and strong......and a pleasure to pull as compared to it's counterparts that are all metal with wood interiors....
                            I suspect your right to a certain degree but lets remember I wasn't planning on putting anything heavy on the trailer. I wouldn't exceed the capacity of the axle which is 3500 lbs. As far as the bolting vs welding? Well I guess my concern was that welding would take some of the temper out of the 6061 aluminum making the beams weaker resulting in more deflection. Put perhaps your right that welding would make it stiffer. Maybe I will go around with the spool gun and put a few welds on.


                            Noel I think your onto something and I agree with you about the 2nd axle. While it would greatly increase my payload that's not the goal here and I think your right in that it would help with the twist some in that it its reducing the span to the front but that's it.

                            Now lets think of the main rail's as if they were just flat bar on edge. Quite strong in vertical deflection but they would twist like a bast*rd. Now add a flange to the top and bottom (Channel) and suddenly it takes a lot more to twist it. If it was tubing then it would resist twisting that much more. Perhaps I should have used Rectangular tubing and I wouldn't be having this problem. Maybe I should box in the channel? A rectangular tube down the middle may help a fair bit as well. Now back to the flat bar analogy... If we added lots of bracing in between it would make it resist twisting as well (think ladder). That's where I'm thinking adding the channel's at the bottom is going to help. Adding gusset of something in between the upper and lower cross member should help as well?
                            www.silvercreekwelding.com

                            Miller Trailblazer 325 efi
                            Miller extreme 12vs
                            Thermal arc 186 ac/dc
                            Lincoln power wave 455m/stt with 10m dual feeder

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                            • #15
                              I've been planning to build an aluminum frame teardrop camper down the road a bit, but in the planning process, I went a looked at how commercially available aluminum trailers were made. I surprised to see everything welded, except the spring hangers, and really great welds at that. There was also a lot more angle than I expected to see.

                              It looks to me like you're playing to your strength, which seems to be boat stuff, and why the trailer looks like a boat trailer. I think there's been some really good input, like welding over bolting, adding the axle and decking to help straighten out the wobbliness. I think you're well on your way to ironing it out.

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