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How to weld a mild steel roll cage

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  • #31
    Definately some interesting information; I'm still practicing on winch bumpers, rock sliders and racks!

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    • #32
      Originally posted by chris***@sbcglo View Post
      Why a digital caliper?
      Since I just learned this 20 minutes ago, I'll try:
      You can zero the digital after reading across the ID, then measure the OD.
      It's what makes the 'no math necessary' happen. The resulting measurement (.134 in my earlier question) will read directly on the digital.
      Last edited by Craig in Denver; 05-07-2008, 01:06 PM.

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      • #33
        I have a story about cage wall thickness.

        When I built my chassis I took it to get certified as soon as I had it welded up. I knew I probably wouldn't get the car done before the 3 year cert ran out (got 1 year left), but I wanted to make sure I had it right before I got any further into the build. NHRA Tech sonic tested the cage and said the main hoop didn't test right? He said it was on the thin side. After he and a second tech had a discussion they slapped a sticker on it. (Sure wish I knew what was said in that little pow-wow that made them pass it). I said does that mean I can continue to build, He said yup, have at it. My son and I jumped in the truck to leave and we both looked at each other at the same time and I said "I don't feel too good about this". Jeff said he didn't either. I was about to sell it as a 10.99 chassis when I happened to talk to a friend of mine who happens to be an X ProMod guy and is involved with our local track. He put me in touch with an IHRA tech and said to have him double check it before I did anything. In the mean time I procured a sonic tester from a construction company who is a customer of mine. I tested ALL the tubes and wrote the test numbers on the tubes. (numbers are still there 2 yrs later). I was getting good readings on all the tubes. I then went to the IHRA tech and he actually got a couple thou. thicker reading than I did. So, I guess the moral of the story is those sonic testers aren't always dead on.
        Every time I see my friend I thank him for having me get a second opinion.

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        • #34
          keep in mind , you NEVER want to have any tube positioned so that if the joint fails it will impail you

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          • #35
            If your sactioning body goes buy S.F.I. specs.you can go to their web sight and get the specs.on the size, thickness and location of the bars for your class.

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            • #36
              I think I saw this mentioned, but it cant be stressed enough, because if you miss this part, then your cage is for nothing.

              GET THE RULE BOOK for the class you want to race in. Build to that. 1.5" .095 wall should fit pretty much anything, so Id say its a safe bet...me in particular, id use 1.5" .120 wall, because in the end, it only adds (at most) 10-15 lbs.

              I also saw the next point I have, on page 2, I believe. Weld out of position. Make yourself as uncomfortable as possible. Wear your leathers, go jogging, come back, put on mask, and cause sweat to run into your eye as you weave into position to weld your practice version of the rear downbar x brace. You will be burned (most likely) and you will definitely not be comfortable.

              I think one of the first projects I ever had to weld into a race car was a fuel cell cage on a 1st gen RX7. I was hugging the differential to steady the gun, and welding about a foot and a half above my mask, with the first spark a nice fat piece of slag met my back, and caused a wonderful dance of agony much to my boss' amusement.

              Aside from that, I think every one else said it best...fitment is key, and make sure you can get 360 degrees on the joint.

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              • #37
                Just one thing to add to the good advice given above... If you are MIG welding a cage or anything else for that matter that puts the arc higher than your upper body or over your head, wear earplugs. I can't even begin to describe how bad it is to get a hot ball of metal in the ear.

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                • #38
                  But I love the smell of earwax and flesh burning together!

                  +1, I forgot all about that pain and anguish.

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                  • #39
                    Originally posted by Speedfab View Post
                    Just one thing to add to the good advice given above... If you are MIG welding a cage or anything else for that matter that puts the arc higher than your upper body or over your head, wear earplugs. I can't even begin to describe how bad it is to get a hot ball of metal in the ear.
                    I know that feeling! But I hate wearing ear plugs because I rely so much on sound when putting in the root bead. It may look OK, but when I can hear it go in, I know it's OK!
                    One other suggestion for working in the above described conditions: I own a leather hood which really helps getting into tight places, combined with an auto darkening lens it really helps!

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                    • #40
                      You can still hear it...its just much more faint, but if you're concentrated on the work, youll still be able to hear it. I like the leather hood thing...I may have to look around for something like that.

                      As far as knowing that the root is in...its 1/8" tube, to 1/8" tube...or 1/8" plate.

                      Any heat or speed problems show up very quickly...not as critical to hear it...for thicker stuff, definitely agree with you though.

                      Thanks for the extra input nocheepgas

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                      • #41
                        Not sure if this has been mentioned ( i didn't read the entire thread) But the NHRA won't allow any MIG welding except where the plate (mount) of the cage attaches to the unibody or frame rails. However on SCCA cages you can MIG the entire thing together in most classes. Everythign I did read was good advice so i just wanted to throw this out there in case you hadn' heard these yet

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                        • #42
                          Originally posted by turboglenn View Post
                          Not sure if this has been mentioned ( i didn't read the entire thread) But the NHRA won't allow any MIG welding except where the plate (mount) of the cage attaches to the unibody or frame rails. However on SCCA cages you can MIG the entire thing together in most classes. Everythign I did read was good advice so i just wanted to throw this out there in case you hadn' heard these yet

                          Nope, NHRA does allow mig welding on mild steel,

                          "All 4130 chromoly tube welding must be done by approved TIG heliarc process; mild steel welding must be done by approved MIG wire feed or approved TIG heliarc process."

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                          • #43
                            Originally posted by Badd00SS View Post
                            Nope, NHRA does allow mig welding on mild steel,

                            "All 4130 chromoly tube welding must be done by approved TIG heliarc process; mild steel welding must be done by approved MIG wire feed or approved TIG heliarc process."
                            Ahh.. I must have grouped mild in with 4130, i'd just enver make a cage from mild if i was going under 12 seconds in the 1/4

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                            • #44
                              There's nothing unsafe about a sub 12 sec. mild steel chassis. In many cases the weight savings MS to CM isn't significant enough to warrant the extra cost of CM. It all depends on the application.

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                              • #45
                                Id have to agree with that...nothing unsafe about mild steel. Didn't the OP say something about road racing though?

                                CM is stronger yes...but go back to high school chem for a second for me...you gain one property and you sacrifice or otherwise compromise for that property.

                                Mild steel is more malleable...it will bend before it shears/cracks/snaps in half.

                                CM is more brittle...vibrations will crack it if they are severe enough. It is however as strong as mild steel, with less wall thickness.

                                Even some GT2 and GT1 class road race cars/teams (2000-2600lbs with up to 650hp) use mild steel in their cages...its all about geometry. The material helps, but the geometry is really what makes the cage.

                                I dont know the exact number of bars in the cars such as the Corvette Racing Vettes...but I know that it is over 20, at least. Even spec miatas have at least 11 to 12.

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