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How to weld a mild steel roll cage

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  • #16
    Originally posted by tasslehawf View Post
    Is there a practical welding test like this?


    Yes, there is, for process piping.

    Comment


    • #17
      Originally posted by FM117 View Post
      Edit
      You want to make up some practice joints. Don't just do em flat
      on a table, do them overhead, sideways, stand on one foot using
      your left hand with one eye closed etc. Do em while your upside
      down with sharp objects poking you in the ribs and back with
      sparks falling down your neck and you can't really see the weld area.
      These are real cage welding practice problems.
      Dave P.
      BINGO! This is exactly why I don't consider myself a real weldor.

      Comment


      • #18
        Originally posted by Vicegrip View Post
        The actual welding is about 5% of the time spent building a good cage IMO. Thinking, planning, drawing, cutting, bending, fitting, cutting, fitting, recutting, fitting and tweeking are about 90%.
        This cannot be stressed enough. Think at least 3 steps ahead of yourself... it'll keep you from welding yourself into a corner... or more importantly a joint that you cant get the backside welded

        Comment


        • #19

          I just read this thread and will agree with everything in the replies, but I believe that there's been one important thing that was overlooked and it will show up during tech inspection.

          Creg stated that he wanted to use .095" x 1.5" tube for the roll cage. I would recommend that he get a rule book from whatever scantioning body this car will fall under and find out what the min. wall thickness allowed is. My point is, lets say, ......... the rule book says that the min. wall is .095", this will be where the problem lies. In the process of bending tubing, the tube will stretch and this will cause the wall thickness to become less than what it is when straight. If the rule book says .095" is the min. thickness allowed, then at most all the bends, in the roll cage, the wall thickness is less than .095" and the car can fail inspection. This is especially true when there are any 90 degree bends involved.

          Having worked with pipe and tubing most of my life and also the building of a few roll cages, this minor point has been overlooked quite a few times by others, until you hit the tech inspections, and that's where you DON"T want to find any BIG problems.

          You might want to check with someone in tech or somebody that does know if this will present a problem. I do know that when you bend pipe or tube something HAS to give and it's the wall thickness that does the giving.

          Just thought I'd bring this up, because I'd hate to see all your work go to waste for something that was overlooked, during your time consuming build.

          Hope this info helps.

          Bill
          Last edited by diverbill45; 04-30-2008, 09:44 PM.

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          • #20
            Good point Bill. When I saw it wasn't an NHRA or IHRA cage I didn't mention anything because I'm not familiar with anything but those 2 sanctioning bodies. I know my mild steel cage is .118" minimum by the rule book. The tubing I purchased from Art Morrison was .134'. I bought some from a speed shop @ .124". Even the .124" you have to mic & be very careful with.

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            • #21
              how do they check the wall thickness?

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              • #22
                Originally posted by Laiky View Post
                how do they check the wall thickness?
                Drill a small hole and use a depth gauge, at least all the tracks that have checked my cages have done it this way. Dave

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                • #23

                  Pro70, ......... There's quite a few different organizations that run different events and most of them have their own rules, so it does make it kinda hard to keep up with all of them. I'm in the planning stages of building a car for the Reno to Vegas run (haven't made up my mind to do it yet, just thinking about it) and they have a different rulebook than the Baja 1000 bunch. I might add that each year some of these rules change, so you have to keep up on everything, each year. I know it's a PITA, but it's for our own safety, and I might add, with this country being the sue capital of the world, each racing organization is just trying to keep these suits to a minimum, when and if this happens to arise.

                  The weekend circle track here, in the town where I live, even has their own set of rules, which leaves a lot to be desired. I've seen quite a few guys get bumped at the inspection, because of this one little item. I heard a few of them say "The rule book says that the min. wall is .xxx and that's what I put in." Some of them just don't understand what happens when you start bending tubing.

                  I just wanted to pass this info along, because after going to all the trouble and expense of building a roll cage, it would be a shame to have to cut it all apart because of not knowing exactly what is required.

                  Comment


                  • #24
                    The groups I design and build to conform to all rule on the wall thickness of the tubing that is used not so much the thickness after forming. The wall thickness inspections holes for the groups I build to (Road racing, no drag or circle) are drilled in straight sections of the main hoop and other major tubes. Most groups, SCCA is a good example, have rules about how tight a bend can be in order to maintain the integrity of the tubing. I would think that the tube wall thickness rules take the elongation and compression of the tubing in bends into consideration.

                    Geometric design plays a great role in the performance of a cage. You can make a cage that uses lots of thicker than called for tubing it will still not be a good cage if poorly designed. I see plenty of cages that have extra tubing that does little and areas that should have has a little more but do not. Things like tube shapes that should make an “X” or “Y” or "V" only intersecting near each other rather than directly opposing each other in self reinforcing nodes. Some builders use square shapes when triangles could have been used. I love triangles, they are the key to geometric rigidity and strength. You can make something strong and stiff by making it massive via Material strength or you can do the same by making it smart via Geometric strength. An “A” is stronger than an “E” so to speak.
                    Last edited by Vicegrip; 05-02-2008, 05:56 AM.

                    Comment


                    • #25
                      Originally posted by dabar39 View Post
                      Drill a small hole and use a depth gauge, at least all the tracks that have checked my cages have done it this way. Dave
                      How do you drill a hole in a tube and measure wall thickness? I'm picturing a depth mic (which would cover the hole), and it would read to the far wall; not just the .134". AND, how big a hole do they drill?

                      Thanks, Craig

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                      • #26
                        The gauge has a hook on the end. You stick the hook in the h o l e and then pull back until the "barb" of the hook contacts the inside of the tube.
                        NHRA / IHRA use sonic meters. Little grease on the sensor to get good contact and hold it to the tube. Care has to be taken to calibrate the meter correctly to get an accurate reading. They always check the straight sections of the tube also. And, bends can only be so many degrees in certain places.

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                        • #27
                          A hook!

                          pro70; Thanks.

                          Comment


                          • #28
                            Originally posted by pro70z28 View Post
                            The gauge has a hook on the end. You stick the hook in the h o l e and then pull back until the "barb" of the hook contacts the inside of the tube.
                            NHRA / IHRA use sonic meters. Little grease on the sensor to get good contact and hold it to the tube. Care has to be taken to calibrate the meter correctly to get an accurate reading. They always check the straight sections of the tube also. And, bends can only be so many degrees in certain places.
                            The hook method might result in inaccurate measurements as it can measure drill hole flash. I scrut for a car club racing league and the standard method is to use a drill and a digital verner caliper. We measure the tube diameter and note the size in the log book. Then I drill a hole, make sure there is no flash at the hole and measure through the hole from outside surface to inside of the tubes far side. Now I zero the digital caliper and directly remake the diameter measurement. This produces the tube wall thickness in the caliper and no math needed. Sounds complicated but it takes about 1 min and is dead on when done right.

                            Comment


                            • #29
                              Vicegrip:
                              I wondered about the inside burr. And, I understood your explanation; that scares me.
                              It was the 'no math needed' that caught my eye and made me figure it out.

                              Thanks, Craig
                              Last edited by Craig in Denver; 05-07-2008, 12:45 PM.

                              Comment


                              • #30
                                Originally posted by Vicegrip View Post
                                The hook method might result in inaccurate measurements as it can measure drill hole flash. I scrut for a car club racing league and the standard method is to use a drill and a digital verner caliper. We measure the tube diameter and note the size in the log book. Then I drill a hole, make sure there is no flash at the hole and measure through the hole from outside surface to inside of the tubes far side. Now I zero the digital caliper and directly remake the diameter measurement. This produces the tube wall thickness in the caliper and no math needed. Sounds complicated but it takes about 1 min and is dead on when done right.
                                Why a digital caliper?

                                Comment

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