Metal stregth question

Hi,
I am not an engineer but trying to understand bolt strgth, tensile strength og steel and some other varribles for something I am wanting
to construct. I am wanting to build a car dolly and/or dual axle trailer. I have welders and have welded on hobby projects but by no means consider myself an expert welder. My idea is to both weld and bolt a square togther to form the frame. I have some 3 inch square tubing laying around, I believe is is 1/8 thick but not sure. It came from some material stand at work that got cut up.
My idea was to get some scrap 1/8 inch plate and torch cut two L brackets and weld them togther to form a inch L bracket. These would go on all 4 corners of the square I would bolt each L with bolts through the L and through the 3 inch tubing. Before doing this I would insert a section of black pipe through all pieces for the bolt to ride in. After bolting and everything being square I would weld all joints with 6011 or 6013 rod with either my AC buzzbox or the mIller generator welder I just aquired on DC. (Not welded with it much yet) (I have trouble welding with 7018 for some reason.
My question becomes, what size bolts would be adequate? I get confused when I see specs on bolts such as shear strength, tensile strength, yield strength, etc? I suspect the bolt need only be as strong as the streth of the bolt steel around it. I am having trouble finding the specs for mild steel strength but think it might be around 38,000 PSI? Is this true?
Any help is appreciated!
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Mechanical engineering is FAR too complex to explain here. See if you can find a used textbook on "Statics". A Physics text would help a lot too.
jsw, who went this route.
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You would be far better off buying a used trailer, than building one from scratch. I built a trailer, but at least I started with A NICE trailer bed from the military.
i

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Ignoramus9757 wrote:

There are trailer plans with engineers stamps for sale from various places. Northern Tool has a collection of them available for various types of trailers.
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Pete C. wrote:

Unfortunately, nothing there that will fill my bill.
I need a trailer for a 26' long x 10' wide sailboat.
6000 pounds would be realistic.
Fortunately shoal draft with a 4' wing keel.
While a flat bed and custom cradle would be the cheapest solution I'd never be able to launch from that without a crane.
--

Richard Lamb



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cavelamb wrote:

The key here is to find the closest match size and capacity wise to what you need and then adapt from there maintaining comparable material specs to the original plans. You need a starting point with appropriately sized materials to base your adaptation on.
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Pete C. wrote:

One issue is that DOT seems to want the trailer to come all the way to the back of the boat - little to no overhang.
The only plans I've found anywhere near that length are for goose neck types.
--

Richard Lamb



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cavelamb wrote:

Most likely a *very* easy issue to resolve. I expect the real requirement is to have a "bumper" area with the plate and lights (particularly the three clearance lights for over 80" width) back there. There are probably no structural requirements for that area.
I expect your functional trailer structure can stop well short of that point, and if you make the frame rails from something like rectangular tube, you can have the extension section telescope from inside that frame out the required distance and lock it in place with a hitch pin on each frame rail so that when you are ready to launch the boat you can remove the hitch pins and push the rear part in and out of the way and lock it in that position with the hitch pins.
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"Pete C." wrote:

I would also note that 10' wide is well over the 8'6" width limit and will require wide load markings and permits.
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Pete C. wrote:

Yep. I know about that. She's for sure fat! (the boat - not the girl!:) )
But the width is all up at the rail and it doesn't really look that wide (until you get the tape out). I don't ever intend to pull it myself. My little Blazer bitched about the 18 - which barely totaled 2000 pounds.
But a trailer would give me a place to "park it" when hauled out.
And make it possible to visit other places.
Normally there are pads on the end of a telescoping tube to hold the boat in place. One clever trick I saw a while back was to use a piece of pipe that fits inside the fixed part, and a floor jack to raise the pads and snug them up against the hull. The guy who built these liked to hear the hull groan! I'm not quite that aggressive, but I still like the trick. That lets the pads drop way down out of the way so they don't interfere with getting the boat centered up on the trailer.
-
Richard Lamb
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Do you think they would notice the joint where it folds upward to be your gantry crane?
jsw
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Jim Wilkins wrote:

??? Ah, Jim, I'm not reading that?
The trailer would wind up something like this one...
http://www.home.earthlink.net/~capri26/trailer.htm
--

Richard Lamb



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Go find a trailer that will work and copy it. My 6000# boat trailer from EZloader had bigger tube than 2". Look at http://www.championtrailers.com/ and look at their parts and axles.
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Hunh, you got pretty much the exact same reply on s.e.j.w, imagine that!
If you keep on trying to bull ahead the way you're going despite getting an aswer you don't like (which your asking the same question over here strongly implies) then the next answer is this: Doing it yourself responsibly will take $60-100+k and four years. Professional liscensure will tack another few years onto that...
You know, maybe $50 or so for a set of plans isn't such a bad idea? Copying a friend's trailer would cost even less.
But it's pointless, since you'll just go ahead and do it your way anyway. I don't understand why you insist on asking for advice you won't follow for every little madcap idea you come up with. Either listen, or just do it the way you want without asking.
--Glenn Lyford
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You know, even if we might hack something together ourselves we shouldn't suggest that in a permanently-recorded public forum.
jsw
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Particularly after being told a better way repeatedly in answer to questions?
--Glenn
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I have no problem copying an existing dolly. My problem is not sure how perfect my welds are. That is why I suggest bolting and welding.
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And I suggested testing them until you know when you've made a strong one.
jsw
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