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  • An open thread for general newbie questions

    This thread is open to all newbies to ask whatever questions that puzzle them. Nothing would be off topic for THIS thread.

    I hate hijacking other peoples threads, but I also don't want to open a dozen threads that might have simple answers.

    I'll kick it off.

    I understand that a proper weld has good penetration, no holes or included slag, and more often than not it looks pretty too. But when is it acceptable to have a weld that is ugly, that has shallow penetration or is porous? Is that OK when the joint is not load bearing, like an angle iron brace that just keeps the load bearing parts in the right orientation?

    For example, I look at the handrails where I work, and I can see where the thin steel supports are welded. The tee joints are welded on both sides but in every case I see that the exposed ends have little or no penetration at the joint. Is that acceptable?


    Thanks

    Dan
    At the end of the project, there is a profound difference between spare parts and left over parts.

    Location: SF East Bay.

  • #2
    And that brings me to question number two.

    How much weld is enough?

    For instance, I welded a shish-kabob stand for a buddy. 3 foot tall by 3 foot wide by 18 inches across. I needed the practice. He'd cut a bed frame (I know, yuck) into the proper sizes and even all the correct angles. All I had to do was weld it. Looking back, I think I over did it. At each corner there was about 6 inches of weld.

    Please ignore the ugliness. It was the worst of the 4 corners and only pictures I have of it.




    Given a tensile strength of 70Kpsi for the welding wire I was using, I think it was overkill.

    What formula does one use to determine how much weld is necessary for jobs like this that will never be called on to do much more than support some hotdogs on a stick?

    Thanks

    Dan
    At the end of the project, there is a profound difference between spare parts and left over parts.

    Location: SF East Bay.

    Comment


    • #3
      Originally posted by danlb
      I understand that a proper weld has good penetration, no holes or included slag, and more often than not it looks pretty too. But when is it acceptable to have a weld that is ugly, that has shallow penetration or is porous? Is that OK when the joint is not load bearing, like an angle iron brace that just keeps the load bearing parts in the right orientation?

      For example, I look at the handrails where I work, and I can see where the thin steel supports are welded. The tee joints are welded on both sides but in every case I see that the exposed ends have little or no penetration at the joint. Is that acceptable?
      it is only acceptable if you dont care if it breaks or what it looks like.

      Without pics dont know.

      Comment


      • #4
        Originally posted by danlb
        And that brings me to question number two.

        How much weld is enough?

        For instance, I welded a shish-kabob stand for a buddy. 3 foot tall by 3 foot wide by 18 inches across. I needed the practice. He'd cut a bed frame (I know, yuck) into the proper sizes and even all the correct angles. All I had to do was weld it. Looking back, I think I over did it. At each corner there was about 6 inches of weld.

        Please ignore the ugliness. It was the worst of the 4 corners and only pictures I have of it.




        Given a tensile strength of 70Kpsi for the welding wire I was using, I think it was overkill.

        What formula does one use to determine how much weld is necessary for jobs like this that will never be called on to do much more than support some hotdogs on a stick?

        Thanks

        Dan
        Coping is the proper way to weld angle, not mitering. See this thread:

        http://www.practicalmachinist.com/vb...e-iron-154580/

        As for how much? Cant really say. That is learned through practice and use.

        Comment


        • #5
          coping is one way to do it, mitring is fine for 99% of the time & unless you have a machine that will cut the cope it is a PITA

          If the weld is full pen & flush or just over it will be strong enough, especially if vee'd or root gaped, or both.

          porosity, inclusions & voids in welds are stress raisers and should be avoided. Unless you are an experienced welder, appearance alone is not sufficient to guarantee a good weld... mig produces some of the best looking weak welds in the wrong hands.

          Part of the learning process must be destruct testing of some work, simple test is weld the type of join you are planning, cut a strip 1-2" wide through the test piece , clean up the weld as normal. Now you can usually see the penetration into the parent material, if not polish the cut edge, Place in vice with the weld maybe 1" above the jaws & bend at least 90deg forward & check for cracking, then bend it back (180deg) if there is no crack it should be structurally sound for almost any amateur purpose.

          with angle/box use longer pieces and try to break the corner... if it fails it should not be on the weld line but off the edge of the HAZ/parent metal

          Comment


          • #6
            Originally posted by macona
            it is only acceptable if you dont care if it breaks or what it looks like.

            Without pics dont know.

            Ok, we'll ignore pretty for now.

            Here's the handrail in question. There are several dozen just like it in the complex that I work in. All look about the same where they are welded.




            And here's the support for it.



            The pictures are from a cell phone; sorry about the quality.

            EDIT: And two more just for fun. A random choice from a different stairwell in the same complex. Two pictures of the same support.






            Dan
            Last edited by danlb; 01-07-2011, 04:22 PM.
            At the end of the project, there is a profound difference between spare parts and left over parts.

            Location: SF East Bay.

            Comment


            • #7
              Thanks for the reference to coping, Macona. Obviously the lay-up of the parts is as critical to structural strength as the welding itself.

              When figuring out how much weld is needed, can one use the tensile strength (in psi) of the filler to estimate the number of linear inches that would withstand the expected load? For example, to hold a 100 pound static load a very small spot weld will do it. ER70S-6 which, if I read it correctly, has a 70Kpsi tensile strength. 100 / 70000 = .001428 square inches.

              Is this even remotely correct? I don't need perfect, but some guidelines for the engineering impaired would help. I can always go twice or 3 times that much to leave a margin for error.

              Dan
              At the end of the project, there is a profound difference between spare parts and left over parts.

              Location: SF East Bay.

              Comment


              • #8
                First an opinion. That handrail is pretty but... it is an accident and or lawsuit waiting to happen. The fabricator, building owner, Engineer and the building inspector will all be involved.

                Welding is a lot about eye hand coordination and that improves with practice. I tend to weld a lot more than is necessary just for the practice. The cutting and assembly are the drudgery so practice by welding all the prepared joints. Appearance is also important so play with the variables where they are not critical to improve it. Sometimes hiding the welds is better. For instance the vertical legs of the table could be inside the top rim rather than outside it. Remember the grinder is your friend the beveled joint could be ground flush and not even be visible. Having the right elements of a structure can make the welded joints stronger. Connections like a bottom tray or cross bracing for the legs would make that table much more rigid wit minimal weight increase.

                As a matter of perspective ask yourself how can I make it better, Not how much is necessary. I am not trying to rain on your parade just supply a little guidance. Welding is fun, enjoy it.
                Byron Boucher
                Burnet, TX

                Comment


                • #9
                  The weld on the handrail is fine. It is tigged and more than strong enough to resist any pull a human will put on it. The anchors will come out of the wall before those break.

                  Comment


                  • #10
                    I would not put my PE stamp on that handrail. There was an article years ago in the old Product Engineering magazine that delt with trying to make things safe and indestructable. Remember the old Dino the Dinouser. Well the first thing the kids did was dump it in the fire. A small table that was constructed for three year olds failed to survive a trip down a flight of stairs. If a pair of four year olds can't destroy that hand rail wait until a skate boarder rides down it.
                    Byron Boucher
                    Burnet, TX

                    Comment


                    • #11
                      My initial concern about the handrail was sort of like Boucher's since the stairwells are emergency routes in case of a fire. The thought that a dozen people could be hanging off it if they tripped during an evacuation...

                      I understand that the hand rail only has to be a bit stronger than the weakest point.

                      But more to the point, I'm trying to understand (without an engineering or mathematics background) what makes things safe enough for low stress, low load uses. I can use that information to extrapolate when I'm under-welding.

                      What I don't want is to make too few good welds If there is a formula or rule of thumb that can be understood to engineer these little jobs, I'd like to learn them.

                      Dan
                      At the end of the project, there is a profound difference between spare parts and left over parts.

                      Location: SF East Bay.

                      Comment


                      • #12
                        I'll have to side with Macona on this one as well.

                        I'd be very surprised if you couldn't hang a piano from that one stanchion alone.
                        There appears to be a very slight undercut on the top side of the fillet weld leg facing the camera, but wetting and penetration appear more than adequate.

                        We have to keep things in perspective here as the most load that this railing will ever see is if someone trips and falls, and then reaches for the railing. I sincerely doubt that two guys with 2x4s could pry it off of it's mount without pulling the anchors first. The stanchion itself may bend but the joint looks sound. Although under normal use this joint would be subject to a bending load more than an ultimate tensile load, don't forget that even one 1/4" grade 5 bolt has a breaking point that approaches nearly 2 tons!

                        Seriously though I've seen guys lift fully dressed big block V-8s complete with automatic transmissions attached, by nothing more than a little tab like the one pictured bolted to the carb mounting flange.

                        This is all speculation of course on everyones part without actually testing the railing.
                        Since Danlb knows where the railing in question is located perhaps he could go in and try to pry it off the wall.
                        Home, down in the valley behind the Red Angus
                        Bad Decisions Make Good Stories​

                        Location: British Columbia

                        Comment


                        • #13
                          Originally posted by Willy

                          This is all speculation of course on everyones part without actually testing the railing.

                          Since Danlb knows where the railing in question is located perhaps he could go in and try to pry it off the wall.
                          I don't think I'll risk my job just to find out if it will break or come loose. thankyouverymuch.

                          All the discussion appears to come back to destructive testing to verify the weld integrity. I guess before I start my next project I will need to weld up some test pieces that I can destroy.

                          Dan
                          At the end of the project, there is a profound difference between spare parts and left over parts.

                          Location: SF East Bay.

                          Comment


                          • #14
                            Dan,
                            Besides doing some of your own destructive testing, LOOK & OBSERVE what others do, especially mass-produced stuff. If a frame under a machine of some sort is made from 1.5 X 1.5 X 1/4" angle, it's probably strong enough, and you'd be wasting time & money by building your version from 2 X 2 angle.

                            It's also important to visualize the force vectors when an item is in use. You can get away with a weld on only one side of [whatever] IF that weld can never be bent into itself. IE: make a butt weld on 2 pieces of flat stock, then bend one end up; the weld will break very easily. It'll be quite difficult to break by bending the other way. If the conditions are such that your weld CAN'T be bent 'up' as in the example above, then it's unnecessary to weld both sides.

                            Chances are, most butt welds will require welds on both sides, but a corner gusset might be fine with a weld on just one side.

                            Comment


                            • #15
                              Originally posted by mike os
                              coping is one way to do it, mitring is fine for 99% of the time & unless you have a machine that will cut the cope it is a PITA
                              +1. Coping is a PITA, and if you're not a great welder, the integrity of the bead is far more important than coping versus mitering.

                              LOOK & OBSERVE what others do, especially mass-produced stuff.
                              I'm not sure that's great advice. The majority of the welds I see these days are bubble-gum welds from semi-skilled labor.
                              I'd suggest hanging out at Welding Web and Weldtalk (Hobart forums) and look at the welds those guys (professional welders) are laying.

                              Like others have said, you need to sit down and practice, practice, practice -- especially on TIG.

                              What's worse, is if you haven't welded in awhile, you definitely lose it. Especially on TIG

                              By the way, that bead on the handrail doesn't look like it's wetted into the tubing, but hard to tell from the crappy picture.
                              Last edited by lazlo; 01-03-2011, 10:36 PM.
                              "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

                              Comment

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