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Question about weld grinding for best appearance

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  • Question about weld grinding for best appearance

    Hello,
    I am building a bumper for my truck and butt welding the joints. when i grind a V joint top and bottom and weld on top and bottom, i get a valley on top of the 2 pieces. When i try to grind the top surface for cosmetic purposes. I end up grinding the surrounding metal because the weld ends up being lower in the valley.
    When i grind a V only on the bottom and weld from the bottom, i get penetration through the top but when i grind that small protrusion flat, I find that there is still a bit of a valley and i end up grinding more of a valley to get a smooth appearance.
    I have attached hand drawings.
    My question is what is the best butt weld/grinding technique to use to get a nice flat appearance on the outside weld.
    Using Miller 180 autoset.

    Thanks in advance for your help.
    Attached Files
    Last edited by digitalwelder; 02-08-2013, 12:05 PM.

  • #2
    What abrasive are you using for the grinding?

    A Flap Disc will do the job, you still have to watch how you remove the weld bead though but they sure are a lot better than a Grinding wheel

    Comment


    • #3
      I use 3" maroon surface conditioning discs and a air powered 3" grinder when I want to get a nice look. I would use a #60 flapper to take off most of the weld and finish with the less aggressive surface conditioning discs.

      http://abrasives4sale.com/qc_discs_scd.htm
      Last edited by tackit; 02-08-2013, 01:50 PM.

      Comment


      • #4
        i'll try the flap disks and the surface conditioning disk. Thanks.

        Comment


        • #5
          GREAT timing and question - thanks! So I was just asked today to repair a metal bracket for some family that is about 3/4" thick. The weld is going to be a butt weld - I was planning on grinding a bevel on all "four" edges - top and bottom side and then using my Thunderbolt 225 XL to run a root pass of 6010 in each side then maybe 7018 pass over the top and grind it down (now with a flap disk first) - cosmetically it doesn't really matter- but I do need to make both sides flat/smooth. Does this sound like the proper repair process?

          Thanks in advance - and sorry for hijacking your thread - but it's basically the exact same question!

          john

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          • #6
            A lot has to do with grinder control and technique. I finish some jobs by lightly going over the work in circles so I don't create a groove.

            Comment


            • #7
              You can get the steel to a mirror finish with the conditiong discs.... but don't try to mig weld over such a polished shiny surface. The weld may not penetrate, just lay on top of the polished steel as though there was proper penitration. I had it happen to me. I think what happens is the heat is either reflected back or the surface becomes so very hard from polishing it effects penetration. Now I always leave what I would call a dull or grained finish when preparing a joint never a polished one..

              Comment


              • #8
                Originally posted by jfk92 View Post
                GREAT timing and question - thanks! So I was just asked today to repair a metal bracket for some family that is about 3/4" thick. The weld is going to be a butt weld - I was planning on grinding a bevel on all "four" edges - top and bottom side and then using my Thunderbolt 225 XL to run a root pass of 6010 in each side then maybe 7018 pass over the top and grind it down (now with a flap disk first) - cosmetically it doesn't really matter- but I do need to make both sides flat/smooth. Does this sound like the proper repair process?

                Thanks in advance - and sorry for hijacking your thread - but it's basically the exact same question!

                john
                I would use a full size grinder with a 7" wheel followed by a 36 grit disc if you need that nice of a finish. I used to do that all the time. A lot of it is grinder control as mentioned. Don't dig with the edge. Smaller grinders are also easier to get a valley with if your not careful.

                Comment


                • #9
                  Originally posted by MMW View Post
                  I would use a full size grinder with a 7" wheel followed by a 36 grit disc if you need that nice of a finish. I used to do that all the time. A lot of it is grinder control as mentioned. Don't dig with the edge. Smaller grinders are also easier to get a valley with if your not careful.
                  Understand...kind of what I was thinking too...thx Mic....

                  Comment


                  • #10
                    jfk92

                    John why are you using 6010? Are you doing an open root then capping it with 7018? Why not just do a 30 degree bevel and butt them and just run 7018. Joe

                    Comment


                    • #11
                      There seems to be a lot of concern about your grinding but if I understand it correctly, you're lacking filler material. You either need to make another pass or two or use a weave on the top weld so that there is sufficient material to fill the void.

                      Comment


                      • #12
                        Originally posted by JMK WELDING View Post
                        John why are you using 6010? Are you doing an open root then capping it with 7018? Why not just do a 30 degree bevel and butt them and just run 7018. Joe
                        Hey Joe! Was looking for your input! I was only thinking a root of 6010 as that is what I've been taught as standard practice for structural joints - with 6010 to get 'better penetration' thus used as the root. But I wasn't sure it was necessary - or if it differs from a butt joint to a fillet weld joint. I think I might forget about the 6010 and just run a couple 7018's - it'll be easier for me!

                        Comment


                        • #13
                          Bevel both sides & weld with 7018 will be fine. If you positively need 100% penetration then after welding the first side root, flip it over & grind out the second side till your into the first weld. Then weld it up alternating sides to minimize pulling.

                          The real question you need to figure out is why did it break in the first place? If this isn't fixed then it will most likely fail again unless it was a one time incident that doesn't normally occur.

                          Comment


                          • #14
                            Flap disk for sure. Impossible to have the control with an abrasive grinding wheel. I like norton multi flaps.

                            Comment


                            • #15
                              Originally posted by Cgotto6 View Post
                              Flap disk for sure. Impossible to have the control with an abrasive grinding wheel. I like norton multi flaps.
                              I disagree with the grinding wheel comment. I've done hundreds of machine bases over the years where all outside seams had to be ground flush. 7" type 28 wheel followed by a 36 grit sanding disc. This is the fastest we found. It's in the technique. Most newbies tend to dig & leave a valley.

                              http://www.mcmaster.com/#type-28-gri...wheels/=lenkx2



                              http://www.mcmaster.com/#standard-sanding-discs/=lenlbj

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