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  1. #1

    Default 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 Images Attached Images
    Last edited by digitalwelder; 02-08-2013 at 12:05 PM.

  2. #2
    Join Date
    Dec 2007
    Location
    Los Angeles
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    2,834

    Default

    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
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  3. #3
    Join Date
    Oct 2005
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    North Central Indiana
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    782

    Default

    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 at 01:50 PM.

  4. #4

    Default

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

  5. #5
    Join Date
    May 2012
    Posts
    108

    Default

    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
    Miller Thunderbolt 225 AC/DC
    Millermatic 211 Auto/MVP

  6. #6
    Join Date
    Oct 2005
    Location
    North Central Indiana
    Posts
    782

    Default

    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.

  7. #7
    Join Date
    Oct 2005
    Location
    North Central Indiana
    Posts
    782

    Default

    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..

  8. #8
    Join Date
    Sep 2005
    Location
    northern NJ
    Posts
    1,825

    Default

    Quote 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.
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  9. #9
    Join Date
    May 2012
    Posts
    108

    Default

    Quote 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....
    Miller Thunderbolt 225 AC/DC
    Millermatic 211 Auto/MVP

  10. #10

    Default 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

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