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question about metal thickness for building frame rails

Discussion in 'The Hokey Ass Message Board' started by goldhunter_2, May 14, 2010.

  1. goldhunter_2
    Joined: Jan 10, 2010
    Posts: 83


    Ya'll be gentle on me :D

    well I guess it would be more of opinions about metal thickness for building frame rails. In the past I have built rail buggy's with tubing and swamp buggy's with square tube trailer frames with Channel and I figured one of those would be the cheapest & quickest way to go for my 31 truck but I got some metal prices today :eek: and just the two rectangular steel sticks would end up costing me almost $600 out the door , so with more time then money I am thinking about doing it like Flthd31 shows in the tech post (link below) but unfortunately I don't have a scrap source like he did so I would just have buy a sheet of steel to cut it out of. I would completely box the frame in as Flthd31 did but would add through tubes for bolts to prevent crushing the frame when torquing down bolts (and hope mine looks half as good as his does :D )

    Now the question , what gauge or thickness do you think the steel sheet material needs to be for construction of a safe frame without to much over kill? this will be a stretched truck frame will be 18' long with 157" wheel base a aluminum rollback bed and will be used for light hauling (drive one boat up on bed and maybe tow a trailer) By "safe" I mean for use as a daily driver light work/hauling at highway speeds equals "safe" Oh one other thing it will have some what heavy of a six cylinder engine with dry weight of 908 lbs and will be using the original cross members and brackets form the 95 dodge 2500

    Witch gauge metal would you consider a safe minim and witch one is beginning to be over kill for construction of the new frame rails ?

    6 gauge (.194)
    7 gauge (.184)
    8 gauge (.164)
    10 gauge (.150)
    11 gauge (.120)
    12 gauge (.105)
    13 gauge (.090)
    14 gauge (.075)
    16 gauge (.060)
    18 gauge (.048)
    20 gauge (.036)

    Flthd31 post link on frame rail build
  2. Most of us use 2x4",5"or6" mild steel tubing which should not cost you anywhere $600! I paid around $80-100 for a stick of 2x5 recently. This was for 1/8th, you would of course go thicker.

    What were you pricing? I would guess that 2x8 should run 150 per stick.
  3. bobscogin
    Joined: Feb 8, 2007
    Posts: 1,761


    So what's the vertical height of the frame rails?

  4. Just priced 2x8" 1/4" wall 20 foot sticks, $360-$400 for two sticks. Pacific Steel warehouse here in the exact middle of the US so there are truck freight costs. Being in Florida I would bet you could at least find it for that or less.

  5. goldhunter_2
    Joined: Jan 10, 2010
    Posts: 83


    T man,
    I priced 2"x 6"x 1/4"x 24' sticks (they carry the 24' not 20'ers) price was $252 each plus tax with me driving up to get them. Are you thinking the material wall thickness needs to be 1/4" ?

    I was think 6" but if I am doing with the sheet steel could go more
  6. I think 1/4 would be overkill on a properly built frame. Have you looked at a factory rollback to be sure? They had no 3/16" wall to price for me, I didn't want to waste too much of his time. ;)
  7. I have always used 3/16". In tubing especially, that would be more than strong enough for frame rails. Channel could go to 1/4".
    Blue One likes this.
  8. goldhunter_2
    Joined: Jan 10, 2010
    Posts: 83


    what about sheet metal thickness if I build like flthd31 did ?
  9. 40chevythrowensparks
    Joined: Aug 16, 2009
    Posts: 100


    i have always heard no less than 1/8... i my self think you would be ok with that...well depending on what you are doing... 1/4 is over kill.... the frame on my 3500 dodge isnt but about 3/16 thick and is hooked to no less than 10000 pounds when i use it...
  10. scottybaccus
    Joined: Mar 13, 2006
    Posts: 4,109


    11 gauge is pretty standard. Don't go overboard. Remember that most C- channel frames were one side of maybe 7 gauge. If you fully box at 11 gauge, you have more than double the material, plus the reinformcment of boxed rails.

    All these home built jobs with 3/16 or 1/4 inch tubing are overkill.
    bill gruendeman likes this.
  11. goldhunter_2
    Joined: Jan 10, 2010
    Posts: 83


    ya I wouldn't have anything that hevay , My big boat ,motor, trailer , full of fuel, plus extra 30 gals for the weekend and coolers and camping gear for three only weighs in at 2250 lbs

    I was thinking maybe 16 gauge but you said you heard 11 gauge or thicker so I mite need to step it up but price still isn't as bad as the tubing was just allot more work
  12. 1934coupe
    Joined: Feb 22, 2007
    Posts: 4,771


    11 gauge is all thats needed and its plenty strong for a big block powered street rod. 1/4" is for battle ships. I have built many 2" x 3" rectangular tube 1/8" (really .120, 11 gauge) and they are still around.

  13. caseyrod
    Joined: Feb 9, 2008
    Posts: 138


    3/16 is more than enough 1\4 is over kill the thicker the waal the more money it woud be
  14. F&J
    Joined: Apr 5, 2007
    Posts: 13,221


    Is this frame for the 4 door truck? Am I reading this wrong as far as frame length? or ?

    18 feet is real short, like a half ton shortbed pickup? I must be not reading it right.
  15. goldhunter_2
    Joined: Jan 10, 2010
    Posts: 83


    no your reading correctly the original 31 chevy 1.5 ton frame specs show actual 213 and 9/16" total frame length I am adding the extra cab but reducing the length of the flat bed area to compensate. only about half the rollback flat bed frame will be on top of the frame (witch allows me to change to regular 6.5' bed sometime in future if I wanted to) I did round the length up form 17.75 to 18' even
    Last edited: May 14, 2010
  16. TagMan
    Joined: Dec 12, 2002
    Posts: 6,202


    !/4" frame wall thicknes??? You guys building hot rods or tanks? :eek:
  17. F&J
    Joined: Apr 5, 2007
    Posts: 13,221


    Well, I know there are a few structural engineers with degrees on hamb, maybe one will chime in with actual span load specs and whatnot for your project.

    It would be good having as much input as possible with a custom build like that...with a cummins etc
  18. F&J
    Joined: Apr 5, 2007
    Posts: 13,221


    yahbut..:D frame wall thickness means little without knowing the height of the rail section, and if C channel or a cummins and rollback and long wheelbase crewcab? not really a standard hotrod.:confused:
  19. Mark H
    Joined: May 18, 2009
    Posts: 1,461

    Mark H
    from Scotland

    1/8th inch wall thickness is ample for a box section frame.Using 1/4 inch is definately overkill and you'll be almost doubling the weight of the frame,requiring more power to get it rolling and more brake to slow it down.
  20. AAFD
    Joined: Apr 13, 2010
    Posts: 585

    from US of A

    3"x2"x.120" wall (11-gauge, or 1/8") is what I've always used, never had a problem. It's cheap, lightweight, can be used in most applications, and easy to get.
  21. I would visit an auto and truck dismanteler yard and look at frames. You might find something that you can kick around some and make a better frame than anything you could make from new material.
  22. gearguy
    Joined: Jan 27, 2010
    Posts: 286


    I'm not a structural engineer but have had to use beam formulas from time to time. Anytime you are building a structure think about the roof of your house. It is the height of the section that has the biggest effect on stiffness. Find a copy of Machinery's Handbook & look at the beam formula. They all reference the "section property" I. For rectanuglar cross sections
    I= BH^3/12, where B is the width of the section & H is the height. For tubing you calculate I for the outside dimensions & subtract the I for the inside dimensions.
    We used 1/4 wall to build stuff that would get seriously abused by fork lift trucks. 1/8" wall ought to be fine for most frames if you have enough "H" in the frame.

    Chuck Schultz, PE
    Winfield, Illinois
  23. 47 owner
    Joined: Nov 25, 2009
    Posts: 9

    47 owner

    Sound like good advice Chuck, please attach a simple hand drawn illustration so we novice folk can see what exactly we have to measure.
    I= BH^3/12??

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