Trailer building

[Cornfed]

I'm building a single axle trailer to assist my B7100 /FEL/Box scraper get around. From an engineering standpoint, which steel is better for the frame, 2x3x3/16 or 2x3x1/4 or 3" channel. I looked around and I've seen trailers built with all three types used for the frame and they were all rated the same. All the knucklehead sales people care about is selling a trailer, no real knowledge. The last two steels mentioned weigh the same (20 ft sections) and the first is about 40 lbs. lighter. Any knowledge out there about whats needed to support my tractor? The bed size will be 80"x14' with 225 75 R15's supporting the load.

 

[RobS]

My Machinist handbook lists 3.00 X 1.50 or 1.75 channels. The Section Modulus is .22 and .37 in. cubed respectively. Flange thicknesses are .20 and .26 and web thicknesses are .13 and .17. The 2X3X1/4 (rectangular tube?) Modulus calculates out at 1.7 in. cubed. This suggests that that the rectangular tube is quite a bit stronger but I'd question these numbers if you say the last two weigh about the same. From this data I'd guess the rectangular to weigh about a third more than the channel.

How strong is strong enough? That depends a lot on the actual trailer design, configuration of the steel elements and build quality. Are you sure you want your tractor on a single axle trailer? Tandems offer a lot more safety margin.

I'm looking to buy a tandem axle car hauler. If I were to try to make one I'd get a book (I think Northern sells one) and generally copy a known good design. Hope this helped /w3tcompact/icons/smile.gif

 

[richfromPA]

hey cornfed,
i also have been playin with the idea of building a trailer. i am a machinist, welder, progeammer, etc. i know when i build mine i will be about the same length as yours. im just wonderin why yer going with a single axle. im sure when yer done you will run into situations when you wish you had the extra axle. the cost shouldnt be a factor if you are gonna go thru all the work involved. as far as which type of structural to go with just remember the most important thing to consider is the design and integrity. most trailers i have looked at are channel. the 2 corners are heavier than the rectangular tubing. if you go with tandem axles you will have more stress when making tight turns. the tires will be dragging instead of turning. there are sites that have plans also or just find a good manufacturer and sneak some pics. good luck
rich

 

[Cornfed]

I agree that cost should not be a consideration, but it always is short of safety. The integrity of the trailer cannot be comprimised. Take a good look at few of the trailers you find for sale, they slap those things together pretty quick and they don't always use the best of materials or craftsmanship. That aside, my tractor/setup weighs about 2,100 lbs. The trailer weight of approx. 1,000-1100 lbs. A single #3,500 Dexter axle would be more than capable of carrying that, if built the correct way. An extra #3500 lb Dexter w/brakes and another set of GoodYear Marathon's and Rims would push the cost of materials up another $750. Right now I'm at about $1,000. Looking around a bit, best I've been able to find is about $1,700-1,800 for what I want. I already have the welder and the space to build, so for me, it's a no brainer. I am leaning toward the 3" channel for the frame and 4" channel for the tongue. I understand what your saying about the towing characteristics of a single vrs. a double, but for me the single is adequate, will corner easier with less wear on the tires and bearings, and yes, it does cost less. Attached is a similar trailer made of 2x3x3/16 and it's rated at 3,500 with brakes. Maybe so, but I don't see it. Of course I'm not a metallurgist. Thanks for the replies, Andy

 

[Jag]

Cornfed, a few questions. Is that the biggest tractor you are ever going to own or property you would want to move. What happens when you are loaded up peddling down the highway and a trailer tire blows... Most all trailers I have seen that a few years old do not have very good tires... they dry rot faster the you will wear the tread. Also have you tried to balance that much weight on a single axle and get it to tow right and get the weight for the bumper pull correct. Around here you can get a double axle single brakes 7000# trailer for a little over $1000 new...

 

[Jag]

CF... I am sorry again. The weights you list put the tractor and trailer right at its' design limits... What about if you need to carry some other building materals or spare implament. Also I have never seen any but commerial operators use a trailer enough to wear tires or bushing (unless you get a very old trailer to start with)... Sorry I guess you got my four cents worth. (two cents twice)

 

[scruffy]

Cornfed, I had a BigTex single axle trailer, as well as a tandem axle car hauler. Would I haul the ol L175 on the BigTex? Not on your life! IF, for any reason your tractor should slip forward from hard braking lets say, you instantly could lose balance (and it don't take much), thus setting you up for a swaying motion that can cause you to lose control. Add the tire blowout issue, and you are in a constant 'Accident looking to happen' status. I would highly recomend that you reconsider the single axle/tandem axle issue, as well as design capability (total gross weight combination) and opt for the larger trailer. You would NOT regret it. IMHO

 

[Cornfed]

I am retired Military- 3rd Infantry Division, and I could listen to every contingency situation that this site could possibly and I could probably think up a few more. Let's be serious, the tractor is secured to the trailer with four 10k ratchet straps. You could lift the tractor/trailer/pickup combination up with these straps and still have weight capacity to spare. Put 80-90% of the weight over the axle and 10% on the tongue and I don't see trouble in figuring that out. The tires have a total conservative capacity of a little over 4k. The #3,500 axle is a conservative number established by Dexter and I am going to pull this trailer (w/brakes) and a Diesel Ram pickup. My initial question was to see if anybody had knowledge of the fatigue strength of the metals that I have seen used on new trailers. I'm not looking for opinions about tandem axle vrs. single axle and what if scenerios. Please try to stay on track and if you have the knowledge to answer the basic question, I would like to hear it.

 

[richfromPA]

hey cornfed,
you have a good point about everyones opinions not being aimed towards yer initial post. i think i would opt for the channel iron instead of tubing. i have made alot of things out of tubing but think channel is more suited for a trailer. if you have 1000 in materials i think you might find a new one that.
rich

 

[Anonymous Poster]

Andy,

If you discourage well-intended input, you will miss a lot, on this list.

I see that you are relatively new here. The responses to questions very often stray, a little or a lot, from the original query. But the original still gets whatever responses are available to it. And nearly always some knowledge/thoughts that you didn't have before will be included in the "extra" material.

To expect that the answers will come precisely as you would like them, nothing more-nothing less, and to express impatience if they do not, is likely to reduce the participation when you show-up with the next appeal for help.

I'm not sure what you were trying to say, when you informed us of your "retired military" status. (?)

Contingencies? I am "retired fire-service" others here are "retired law-enforcement", etc., etc., Dealing with what-might-happen is not a "military" exclusive. And most here appreciate any and all well-meant suggestions, ...although they often are repetitious, having been thought-of, mentioned, or discussed-at-length before.

The least-effective officers (your tone gives me the impression that you "were" an officer, ...I could be wrong, of course) in any organisation are those who cause their men to be reluctant to "offer" ideas freely. ( If I am right about your "rank", welcome to civilian-life, ...things are different here /w3tcompact/icons/wink.gif )

"Don't tell me anything except EXACTLY what I want to know!" is likely to be interpreted by many as "Don't tell me anything!" And you may get an appropriate response.

If (IF) the problem is that you resent "wasting" the time it takes to read the "extra" material, ...consider the time taken by others, to sit down and type what they hope will be helpful to you, with "nothing-in-it for them, but the rewards (as most of us see it) of participating in this fine group.

Sorry I don't have any metals-specific data/recommendations for you. Consider this some of that "extra" input.

FWIW

Larry /w3tcompact/icons/smile.gif

 

[TresCrows]

Well, I am not retired anything and proud to be a wild and wooly civy and could care less anyway. That aside, I have some training and knowledge of metals and matierial strength and I am a bit confused as to why this is an issue? Most of these trailers you see are built from mild steel, probably a 1000 series alloy. I doubt it should be a concern if the trailer is sufficiently over built, fatigue life should be in excess of the remainder of your life. When the elastic limit is exceeded the metal takes a new shape--it bends, depending on the type of metal, working below the elastic limit to calculate fatigue cycle life--depends to what percent of fatigue strength the metal is worked repeatedly. If the metal is so oversized that it simply does not give then it is not "cycling" and limit life would be infinite excluding corrosion effects etc. If you want an expensive last forever trailer build it from heavy wall, 4130, chro-mo steel, seal the tubes and inject tube seal or linseed oil in the tubes and zinc chromate the exterior surfaces and then paint the hades out of it with polyurethane paint--something like Dupont Imron. That would be way overkill but the stuff has about 3 times the strength of mild steel, 30,000-50,000 psi vs 90,000-120,000 or better for high strength steel--4130 and similar high strength alloy steels. This is without reference to text, off the top of my head numbers and a vastly over simplified attemted explanation for a very involved and complicated subject I am not involved in on a daily basis. I doubt people calculate fatigue life of trailers, they just grab some chunks of steel, weld it up and say that looks about right. J

 

[Bird]

I agree, Larry. It reminds me of when, in my prior occupation, we had a somewhat eccentric character running the "body rebuild" shop. And I lost count of the number of times I went to him with an idea and asked whether he could fabricate what I wanted, but I think every darned time I did, he said, "Sure I can, but what about if I . . .." And you know, I think he had a better idea every time. I love guys like that!

Bird

 

[Cornfed]

Your post reminds me of what a Law Instructor once said to a class I attended, "The internet has opened up a whole new world, where anyone can be anything, and they will say or comment on everything just so that their voice will be heard." Thanks for the "Extra Input".

 

[Cornfed]

Your attitude may be why it was your previous occupation, or maybe you never quite knew where those gray areas were for you to expand on. Thanks for the "Extra Input".

 

[Cornfed]

My reference to "Retired Military", meant that I didn't just fall off the turnip truck, no offense to others. Thanks

 

[Anonymous Poster]

/w3tcompact/icons/laugh.gif /w3tcompact/icons/laugh.gif
"wild and wooly civy" " could care less anyway" !! Thanks TresCrows, for the laugh, ... good place for it! /w3tcompact/icons/wink.gif

Larry

 

[Bird]

Gosh, Cornfed, I'm shocked /w3tcompact/icons/shocked.gif that you'd get off topic that way. I thought you didn't want anyone doing that./w3tcompact/icons/wink.gif And the reason it was my "previous" occupation was that I had other things I wanted to do, so I retired just short of 25 years in spite of them trying to talk me into staying./w3tcompact/icons/laugh.gif And yes, on this forum we do tend to get off topic, some responses to questions go far beyond the original question, and in the process a lot of friends learn a great deal from each other, and have fun doing it. I realize it isn't the best format for everyone, but hope you'll join in and enjoy it.

Bird

 

[Cornfed]

I apoligize, I really didn't mean to rub anyone the wrong way with any of my replies. Just sending out replies and sometimes they might cut to the quick. Andy

 

[Anonymous Poster]

No Problem andy /w3tcompact/icons/smile.gif ,

This is a "country" road, ...little bumpy sometimes, but still a great place to be !

Welcome aboard /w3tcompact/icons/laugh.gif ,

Larry

 

[Anonymous Poster]

Andy,
About that military-service:
I sometimes stop someone I see with a "Nam" ribbon bumper-sticker, just to say "thanks", and shake their hand.
I don't know when/where you served, but I'd like to extend the same appreciation to you. Hats off!

Sincerely, /w3tcompact/icons/wink.gif

Larry [ LHSmith @wvi.com ]