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this is probably the worst idea ever but...

Discussion in 'The Garage' started by 87k10, Feb 24, 2006.

  1. 87k10

    87k10 Registered Member

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    has anyone built a cage out of square tubing? i dont have the money to buy a tube bender, and mess up a lot of tubing before i learn to do it right. i dont think it would be as strong but, with a good design do you think it would work? i have an 87 pickup (well the cab is still there) and want to put an interior cage in it.
     
  2. 87k10

    87k10 Registered Member

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    everyone replies to a ?'s like using 90w in thier diffs but not this?
     
  3. surpip

    surpip 1 ton status

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    wow you gave it a whole 10min before becoming "the most important member on the board, reply to my request right now"
     
  4. cbbr

    cbbr 1 ton status GMOTM Winner

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    Be paitient. Diff oil does not exactly require fabrication experiance, a lot of us have done that before. It also can't kill you if done wrong.....
     
  5. 87k10

    87k10 Registered Member

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    sorry its not like that, i didnt mean to jump the gun! i just am about to go outside and i will be working out there most the day. i am very impatient sometimes. i have the chance to get a lot of 2x2 tubing for FREE!
     
  6. marv_springer

    marv_springer 1/2 ton status

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    Make some gates or something else outta your [ ] tube. Sell them and buy round for your cage...

    You'll be glad you did.

    Marv
     
  7. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Yes, be patient. Everyone who can help you is not sitting there just waiting for you to post. The person with the best help for you may not log on until tonight, tomorrow, or the day after.

    Round tubing is used because it has the same strength (modulo bends and supports) when dealing with input forces from any direction. Square is much stronger when dealing with force loads oriented parallel to it's sides. Properly oriented force is like bending strap stock "the hard way" with the addition of stretch/compression resistance due to the top and bottom walls. But it is relatively weak dealing with loads across the corners where it wants to "diamond" and acts more like strap stock bent "the easy way". As such, it is not good for a cage where forces may come in from any direction.

    This can be somewhat mitigated by use of “node” design and triangulation to convert bending forces into tensile/compressive forces. And of course it has no affect for internal bracing where bending loads are not seen, but there is also the aesthetic appeal to consider in many cases.
     
  8. Leper

    Leper 1/2 ton status

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    One day I hope to completely understand everything you just said, in function and mathmaticly.

     
  9. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    What part was hard to understand? I try to keep it moderately short because people complain when I write "a book"...
     
  10. The Butcher

    The Butcher 1/2 ton status Premium Member

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    Well, how about this for example: "Properly oriented force is like bending strap stock "the hard way" with the addition of stretch/compression resistance due to the top and bottom walls."

    What is strap stock? How about "the hard way"? Not trying to be a smart a$$. I legitimately don't know what that sentence means. I understood the sentence that came after that one though except for once again the reference to "strap stock" and bending it "the easy way".
     
  11. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Strap stock is also called flat bar. For instance, 1/4" x 2" strap stock. Bengine the "easy way" is to bend it like it's laying flat across your knee, so the bend is 2" wide. Bending it the "hard way" is turning it up on end, so the 1/4 side is across your knee, and trying to bend it that way.
     
  12. Leper

    Leper 1/2 ton status

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    I am well on my way to understanding now.:doah: :haha:

    Splain this

    "This can be somewhat mitigated by use of “node” design and triangulation to convert bending forces into tensile/compressive forces"
     
  13. dleroy43

    dleroy43 1/2 ton status GMOTM Winner

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    The dohickey connects to the thingamicbob in an uncumftable position to prevent tweekage :waytogo:
     
  14. Leper

    Leper 1/2 ton status

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    Why didn't he just say that?
     
  15. pauly383

    pauly383 Daddy383 Staff Member Moderator

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    Russ is the coolest guy to talk to . He has a great good ol boy accent , but only spews forth intelligent conversation :bow:
     
  16. 87k10

    87k10 Registered Member

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    i knew it was a bad idea, but i just wanted to know why. thanks badog for explaining.
     
  17. surpip

    surpip 1 ton status

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    that means if ya doint weld the **** together right, when you crash you will die cause the cage will collapse
     
  18. Ronnie4wd

    Ronnie4wd 1/2 ton status GMOTM Winner

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    Almost swedish so now even I can understand:bow: :bow: :bow: :wink1:
     
  19. blackblazer717

    blackblazer717 1/2 ton status

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    you will die cause when it collapse's in on itself its probably going to impale you real bad...hehehe
    bad idea

    LUKE
     
  20. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    That's actually pretty accurate. :D

    I'm just talking about proper use of triangles where you can, combined with "nodes" for joints where possible. The ideal is that you want to build your cage from triangles with straight sides. Ever notice how you can create a triangle with ball joints at all 4 points, then grab the points, and you can't distort the shape? Try that with any other 2D geometry and it will flop around all over the place. Now imagine you built your cage from a bunch of triangles and all the points of all the triangles meet at the same points. These points would be called "nodes".

    Now further imagine that your cage built from triangles, connected together at nodes so it has the shape a cage should have, gets hit hard right above the driver’s door by a boulder in a hard roll. That bar will undoubtedly deform, probably flatten and bend inward a bit, BUT (and here is the key), for it to bend very far the ends of the bar must get closer together! Shortest distance between 2 points and all that. If the bar is not straight, and the length of metal remains roughly constant, the end points MUST get closer together.

    But remember those nodes at all the end points? The nodes that connect triangles together? For that bending bar to get bent very far, those *nodes* have to come together (assuming the welds or material does not fail altogether). Which means your pulling those other rigid triangles around by their nodes. So what you have done is convert bending loads (tube FAR weaker in bending) to linear compressive/tensile (stretching) loads along the tubes that form the triangles (and tube is MUCH MUCH stronger with these loads). Furthermore, because the triangle shape itself is rigid if you don’t deform the tube (through a bending load generally) you transfer those forces through out the cage, which has now become something known structurally as a “space frame”.

    But note the earlier qualifiers "where you can" and "where possible", that's part of the compromise between full on pro cages and what you find in a trail rig. In the real world, a typical rig (even for comp) will make some compromises for ease of access to seats, storage, maintenance, etc. And you won’t be able to have all your tubes straight, or ideally oriented triangles to transfer forces perfectly. So you’ll wind up with some bent tube (in a proper bender), and some squares where triangles might be better, but by knowing what your looking for you can build a MUCH stronger cage that is lighter than a cage that will not hold up as well.

    So, triangulate and use “nodes” to transfer energy where you can, and compromise where you must. And the MOST important place of all is in the b-hoop (arch behind the front seats) to keep the whole cage from folding over in a side hit (like the all too typical open “box” cage can do). This happened to one of the AZ guys when his Land Cruiser went over on the way to a trail. Power slide on a dirt road at 20ish mph, caught a burm, did a hard flop (don’t even think he went all the way over, maybe 3/4(?)) and his square box of a cage now is a trapezoid offset on the top by about 8”. No doubt saved his life, and it had done slow flops before with no major issue, but a simple diagonal on the b-hoop would have kept it serviceable after that hard flop…
     

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