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Thread: question about structural integrity of home made aluminum trailer design/process?

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    question about structural integrity of home made aluminum trailer design/process?

    Hi, sorry to bother you. I'm planning on making an ultralight trailer and I was wondering if it will be stable enough, and if it's better for me to buy or rent the equipment I need or send it to a shop to be welded together (and how much woudl the shop maybe charge? I am a machinist but I've only done a little bit of welding and have no tools or experience to do aluminum.

    My priorities are to make a trailer that is basically just big enough for a bed while making it as light as reasonably possible without compromising too much on integrity. My plan is to base it on a welded aluminum frame using a split torsion axel, with a distribution system that uses a solid aluminum bar core for the axle substitute, a 2" hollow bar from hitch to tail as a spine to support a 1" hollow bar frame, a thin sheet of something rigid for the bed, then a lightweight shell with .75" or maybe .5" angle bar for support and with rigid foam with a truck liner exterior and not sure what for the interior yet. I haven't figured out what i will do for doors as it seems it's best to buy premade.

    My current estimate is that the trailer will weigh about 400-600lbs and cost about $2,000-$3,000 excluding doors and fixtures that will likely add another grand. Plus I'll likely need help with the welding as I don't have the right equipment so that will cost more

    The pictures are as below. the dark pads are solid aluminum for bolting on the split torsion axel along with the stabilizer jacks (using one in the front instead of a standard jack because the trailer will sit low to the ground - my car is also low profile anyways)

    i intend to put two doors on either side that are as big as possible, I don't think i can make them from scratch and be fully weatherproof so I need to find ones that aren't full height and make adjustments to fit them. then add some windows i can open, a roof vent, wiring and bolt on a coupler, and it should all be good to go.

    I'm still figuring out exactly how I want to do the upper shell, as I'd like to have rounded edges.

    http://www.cerka.ca/trailer-jack/stabilizers/78-770203-650-lb-stabilizer-jack
    https://www.teardroptrailerparts.com/doors.html
    http://www.cerka.ca/trailer-axle/half-axles/19-fr-14-4-1400-1-2-axle-set-4on4?sort=p.price&order=ASC
    https://www.amazon.ca/Milliard-Tri-fold-Mattress-Removable-Non-Slip/dp/B00W67PEY2/

    Oh and heres the file i'm working with. It's the educational mastercam file format so opening it is going to be an ordeal in itself unless you also get educational mastercam https://1drv.ms/u/s!AsIQJ23rEAwFhpY1...ZyMag?e=rp4hxj
    Attached Images Attached Images   

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    Re: question about structural integrity of home made aluminum trailer design/process?

    IMO if you have never welded aluminum then I would HIGHLY recommend sending it to a shop. I'm a retired Machinist also and would expect that you know that aluminum is a completely different animal, I once knew a welder that said he didn't even consider aluminum to be metal. If you should decide to weld it yourself then PLEASE do everyone else on the road a favor and not do it until you have gotten very proficient in aluminum welding, you're assuming a huge amount of responsibility.
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    Re: question about structural integrity of home made aluminum trailer design/process?

    I guess that's what I should've expected. Is it better to order and cut the bars myself or get the shop to handle all of that too? I'd like to get a cost estimate but I suppose it's way too early to get anything remotely close to an accurate estimate.

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    Re: question about structural integrity of home made aluminum trailer design/process?

    Go look at commercially available ones.

    there are some nice little fibreglass ones, with windows, aerodynamic shapes, all ready made, tested, certified for the price you mention.


    Steel flexes and fails slowly, aluminum cracks suddenly totally.

    There are no aluminum axles.

    There is huge galvanic reaction corrosion between steel and aluminum where your body meets the axle and springs.
    Last edited by 12345678910; 4 Weeks Ago at 07:30 PM.

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    Re: question about structural integrity of home made aluminum trailer design/process?

    Having built a small lightweight trailer to tow with my Fiesta back in the eighties I have a bit of first hand experience. I like the thinking and approach but have two suggestions. 1) The axle placement looks to be centered. Consider moving to the rear for improved tow ability. 2) Although the slope on the tail looks cool, you are giving up valuable space. I suggest raising it to provide more space at minimal impact on weight.

    Iím also a former machinist and own a mig welder but have yet to do aluminum.

    Good luck and keep us posted.


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    Re: question about structural integrity of home made aluminum trailer design/process?

    Axle placement doesn't matter. How the trailer is balanced does.

    For a light weight trailer with a light load that won't transfer much to tongue weight no matter what you do, then I would agree with an earlier comment that the axle should be more towards the rear. The more weight forward of the axle the more stable it will be.

    However, 10-15% tongue weight is the recommendation on a bumper pull (you can get up to 18-25% with a gooseneck/5th wheel, but that is also with a vehicle equipped to take the weight - and, say, 20% of 14,000lbs is 2,800lbs - thats alotta extra weight on the rear axle!).

    If your trailer weighs, loaded, 800lbs 10% would be just 80lbs. Your car is going to squat pretty easy but if you can get up closer to 200lbs tongue weight it would be really stable (160lbs being 20%). On that light of a trailer less than 15% tongue weight doesn't make much sense (120lbs).

    As to the tapered rear - that will help with aerodynamics. If you can eliminate the flat back end and the eddy currents/turbulence in air that causes (as air moves over that shape and around it the flat back end goes to lower pressure) you can decrease your air resistance.

    If you want to experiment with fiberglass you can make a wood or foam mold of the shape you want then layer fiberglass on. Fiberglass is pretty darn messy stuff, though, so definitely be careful if you decide to tackle it. Though, you can make some pretty darn cool stuff with fiberglass.

    Just a thought on the other end of the coin of put the axle further back - if you leave the shorter wheelbase the trailer will track closer to the tow vehicle. That is as opposed to the axle further back where it will swing further away from the tow vehicle's tracks in a turn. The shorter wheelbase will make backing up the trailer a lot harder, but with that small of a trailer you can probably drop it and push it by hand if you have to. Otherwise, if you are maneuvering, say, in a shopping center parking lot with those planter "islands" in the parking lot you can get through there with traffic a lot easier with a shorter wheelbase.

    Here is a video on trailer stability vs loading:
    Last edited by FlyFishn; 4 Weeks Ago at 11:54 PM.

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    Re: question about structural integrity of home made aluminum trailer design/process?

    How far back should I shift the axle? I never did find a good ballpark for calculating ratios. One thing is that the torsion axel moves the wheels back about 11 inches, the roof taper makes the front a bit heavier, and the front tapered section and tongue does make it stick out a little further forward. Yeah I can consider reducing the back taper a bit, tbh it does look a little funky, but I haven't even started to make a proper plan for how to do the shell, except maybe use 0.75" angle iron inside out so I can stuff them with filler to make the edges have a radius, then some sort of rigid insulation as a base and thin panelling on the inside and truck liner on the outside.

    And the torsion axles are bolt-on so I don't think they should galvanize that badly? They are supposed to be a softer ride which should reduce shaking and vibration, but I could also fill the frame with spray foam to reduce vibration.

    And I've been looking for premade ones for some time. It's been rather tricky finding anything used or new that wasn't ungodly expensive or out of stock. I thought the prolite Suite would be a good alternative, but it is a bit bigger and wider and I've had a hard time finding a dealer. Most people here get big trailers to tow behind their trucks.

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    Re: question about structural integrity of home made aluminum trailer design/process?

    Quote Originally Posted by FlyFishn View Post
    Axle placement doesn't matter. How the trailer is balanced does.

    For a light weight trailer with a light load that won't transfer much to tongue weight no matter what you do, then I would agree with an earlier comment that the axle should be more towards the rear. The more weight forward of the axle the more stable it will be.

    However, 10-15% tongue weight is the recommendation on a bumper pull (you can get up to 18-25% with a gooseneck/5th wheel, but that is also with a vehicle equipped to take the weight - and, say, 20% of 14,000lbs is 2,800lbs - thats alotta extra weight on the rear axle!).

    If your trailer weighs, loaded, 800lbs 10% would be just 80lbs. Your car is going to squat pretty easy but if you can get up closer to 200lbs tongue weight it would be really stable (160lbs being 20%). On that light of a trailer less than 15% tongue weight doesn't make much sense (120lbs).

    As to the tapered rear - that will help with aerodynamics. If you can eliminate the flat back end and the eddy currents/turbulence in air that causes (as air moves over that shape and around it the flat back end goes to lower pressure) you can decrease your air resistance.

    If you want to experiment with fiberglass you can make a wood or foam mold of the shape you want then layer fiberglass on. Fiberglass is pretty darn messy stuff, though, so definitely be careful if you decide to tackle it. Though, you can make some pretty darn cool stuff with fiberglass.

    Just a thought on the other end of the coin of put the axle further back - if you leave the shorter wheelbase the trailer will track closer to the tow vehicle. That is as opposed to the axle further back where it will swing further away from the tow vehicle's tracks in a turn. The shorter wheelbase will make backing up the trailer a lot harder, but with that small of a trailer you can probably drop it and push it by hand if you have to. Otherwise, if you are maneuvering, say, in a shopping center parking lot with those planter "islands" in the parking lot you can get through there with traffic a lot easier with a shorter wheelbase.

    Here is a video on trailer stability vs loading:
    I didn't see your post until after I finished composing my post sorry. Yeah, I'm pretty confident in the weight balance on the thing. The torsion axle moves with back a little further, and the front part will have two doors installed, and when travelling I'm likely to fold the trifold mattress to shove towards the back and use the front part for cargo.

    The trailer is a little narrower so I should have good visibility through my side mirrors (but I may misguage how long my trailer is until I get used to it.) and the front taper should help me avoid jackknifing as I can easily see when the angled panel is getting close to my bumper.

    I'm hoping that the central spine thing works well, I'd make sure it's welded onto the psuedoaxel really well as the torsion half axels are not physically connected to each other except by being both bolted to the same frame.

    I'm still trying to figure out exactly how I want to do the frame to make it as light as possible without going crazy with materials. My main plan is to use 3/4" ridged insulation foam with a truck liner outer coating, but I'd need a minimal aluminum frame to add support and hold on parts like the door. Not sure what to do for the interior, but I'm eyeing 1/8" plastic panelling for the sides and roof and 1/4-1/2" plastic panning for the floor. Ideally something somewhat insulating.

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    Re: question about structural integrity of home made aluminum trailer design/process?

    Quote Originally Posted by grahamf View Post
    How far back should I shift the axle? I never did find a good ballpark for calculating ratios. One thing is that the torsion axel moves the wheels back about 11 inches, the roof taper makes the front a bit heavier, and the front tapered section and tongue does make it stick out a little further forward.
    The weight equation (the 10% or more on the tongue) is based off the loaded, as-rolling-down-the-road, weight. That is not on the empty weight of the trailer/frame/structure as-built.

    So what you intend to cart along with you - how you build the inside out (cabinets, what do you put in the cabinets, electrical stuff, bed, dresser, what have you) will factor in to the weight.

    That having been said, you can also use how you build the trailer out inside to get the balance you want.

    All of that having been said....

    As to where to move the axle in the design - there is no answer to that based on weight balance without some idea of knowing how you want to build the inside out and what all that "stuff" weighs.

    With as small/light of a trailer as that is - balancing the trailer would be pretty easy. If you carry water, for example (you can get 5-7 gallon jugs at Bass Pro, Cabelas, etc) you can move the jugs around while rolling (as long as you find a way to secure them so they stay put). That would act as some level of ballast to shift the weight around.

    For starters - if you want to go after the "more tongue weight" scenario (as opposed to the short wheel base) - have the axle (where the center of the wheels are, not the center of the axle - it appears your torsion bar axle is off-set quite a ways - center of the wheel will be the "tipping point" and where the weight rests) positioned at the last 1/3 of the trailer body. Looking at your underside of the design - I assume the double black crossbars with the plates are for the axle mounting - if you shift that rearwards so the axle (again, center of the wheels) is about 2 cross bars from the rear of the trailer that should get you in the ballpark. If it is that far back I doubt you'd ever have to worry about the tongue weight being too "light". As to how heavy you want it - that depends on how you load it.

    Red = axle center (center of wheels axle, not axle frame axle - again, the tipping point/weight carrying point is the center of the wheels, not the axle frame forward of the wheels)

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  12. #10
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    Re: question about structural integrity of home made aluminum trailer design/process?

    Good trailer shops will know where to put the axle. A trailer, especially aluminum is not the thing to build for your first welding project.

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    question about structural integrity of home made aluminum trailer design/process?

    Iíve built (or rebuilt) a couple steel trailers myself.
    In my experiences, especially if your starting from scratch, I have determined that itís cheaper and much less headache and work to just buy one. They are engineered and thatís important.
    Last edited by snoeproe; 4 Weeks Ago at 08:08 AM.
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    Re: question about structural integrity of home made aluminum trailer design/process?

    Always used the rule of thumb 60/40 on trailers, 60% in front of axle/40% behind axle. usually gets you pretty close on a tongue pull.

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    Re: question about structural integrity of home made aluminum trailer design/process?

    This is really a tough one. A trailer is a cyclically loaded structure that can and will fatigue at the weld HAZ if not post weld heat treated. Unless the designer is a very talented structural engineer with metallurgical and weld expertise dealing with aluminum, the design could and probably will spell disaster. There are codes for DOT design, construction, and repair for transportation vehicles and trailers that really are eye poppers. Construction and repair deal with specific alloys, fillers, preheat, and interpass temperatures. Simple 4000 series fillers cannot be used without heat treat. 5000 series filler must be used with caution.

    The 5000 series fillers when used for welding will involve some base metal dilution of the parent metal. The heat generated will detemper the HAZ. With a low preheat, minimal heat input, and maximum interpass, the HAZ can strain harden back up to some temper that will allow natural aging to regain some strength in the HAZ over a few short weeks. It is imperative that no load or stress be applied to the HAZ for some few weeks to not cause premature fatiguing.

    Most very competent weldors can weld steel with impunity but are clueless to the mechanics of alum. I would recommend a newbie stick with steel.
    Weld like a "WELDOR", not a wel-"DERR"
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    Re: question about structural integrity of home made aluminum trailer design/process?

    Quote Originally Posted by snoeproe View Post
    I’ve built (or rebuilt) a couple steel trailers myself.
    In my experiences, especially if your starting from scratch, I have determined that it’s cheaper and much less headache and work to just buy one. They are engineered and that’s important.
    Especially buying lightly used ones. Much cheaper than building and way less hassle.

    I just bought a used gooseneck and the work involved to have built it myself would be crazy - I don't have the kind of time...
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    Re: question about structural integrity of home made aluminum trailer design/process?

    Yeah I think I'd just save a lot of hassle and get a professional shop to weld it. I do have a friend that has done some aluminum welding so I could ask him, but with all of the welding that has to be done I'd have to pay him anyways. I'll likely tweak the design a little, making the side beams a little bigger and extending the cross members, and add a small tapered boss to the rear end. I figured I'll make the upper frame out of round tubing to get the radius, then I'll update my model so I can calculate the weight and cost estimate. This trailer I doubly will weigh more than 600lbs and the independent suspension should reduce strain, so I think I'd like to believe it will hold up fine.

    I do admit that just buying one would save a lot of hassle, but the main thing is that I haven't been able to find one. My car can in theory tow 2,000lbs, but anything over 1,000lbs should really have brakes. There are a few models that do exist that would work, but they are impossible to find used and cost more than I can really afford.

    That's largely a moot point anyways as it will take a year or two for me to actually start on this project. When I have a better model I'll run it by someone who can tell me if it's workable or not.

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    Re: question about structural integrity of home made aluminum trailer design/process?

    It will cost you more to build one or have a shop build one for you. It's Cheaper to just buy it new.
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    Re: question about structural integrity of home made aluminum trailer design/process?

    Quote Originally Posted by snoeproe View Post
    I’ve built (or rebuilt) a couple steel trailers myself.
    In my experiences, especially if your starting from scratch, I have determined that it’s cheaper and much less headache and work to just buy one. They are engineered and that’s important.
    Even more important is that the manufacturer has to be listed on the registration. If homebuilt that would be you. That is so the lawyers will know who to come after when things go bad.
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    Re: question about structural integrity of home made aluminum trailer design/process?

    The design looks inappropriate for an aluminum trailer, which should have heavier outside rails, and be bolted together, like my boat trailer, not welded.


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    Re: question about structural integrity of home made aluminum trailer design/process?

    Fair enough. My intention is that the trailer would not be carrying that much weight anyways, at most 500lbs. My question then is if I can rework this into a steel trailer then, replacing the central spine with a slightly thicker outside rail, removing some of the horizontal beams, etc.
    I was hoping to make s trailer that would last without corroding or calling apart but if the design isn't workable then oh well

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    Re: question about structural integrity of home made aluminum trailer design/process?

    I've redesigned the frame to use .065" steel tubing, 2x2" for the hitch and main axle crossbeam, 2x1" rectangular tube for the main frame, and 1.5x0.5" rectangular tube for the crossbeams and sub frame. running it through a shopping tool it's approximately 310lbs not including axel/suspension and shell, but it's likely significantly stronger with the weight still being within the comfortable limits of my car's towing ability.

    Does that look a fair bit better? it'll be easier to weld securely anyways

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    Re: question about structural integrity of home made aluminum trailer design/process?

    Just looking at it, and I'm no expert in trailer design, but the "Main Frame" (perimeter?) is 1X2? What are you going to attach the axle's spring perches to? The 1" side?

    How's that gonna work?

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    Re: question about structural integrity of home made aluminum trailer design/process?

    half axels. i weld a 4x6" plate to where the 1x2 and 2x2 are welded together then bolt them to the axles
    https://www.southwestwheel.com/p-231...rcle-hubs.aspx

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    Re: question about structural integrity of home made aluminum trailer design/process?

    I agree
    I have built trailer and used steel.
    Aluminum has a place but it does not get along with steel.

    I used steel for the frame and aluminum deck. Knowing sooner or later I would need to work on the aluminum.

    But I live were it dry and salt is not used on the roads or near the ocean.

    Dave

    Quote Originally Posted by 12345678910 View Post
    Steel flexes and fails slowly, aluminum cracks suddenly totally.

    There are no aluminum axles.

    There is huge galvanic reaction corrosion between steel and aluminum where your body meets the axle and springs.

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    Re: question about structural integrity of home made aluminum trailer design/process?

    Quote Originally Posted by grahamf View Post
    I've redesigned the frame to use .065" steel tubing, 2x2" for the hitch and main axle crossbeam, 2x1" rectangular tube for the main frame, and 1.5x0.5" rectangular tube for the crossbeams and sub frame...
    Way too lightweight. Get rid of all the cross bracing and add the weight into the frame.

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    Re: question about structural integrity of home made aluminum trailer design/process?

    I think you're over thinking it. I'd probably use a 1 piece axle. Look at some commercially availalble trailers.

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