Butt welds

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Hi. Totally newbie question so please bear with me.I'm butt welding a floorpan replacement using a Lincoln weldpak 100, with .23 wire and C25 gas.  I started out with volts on A and wire speed at 2.5, but I wasn't getting any penetration. The weld would just ball up on the surface. So I increased volts to B and got penetration on the new part, but started blowing through the old part. Finally got it to stick by going back to A and using a copper backing strip which lets me move slower.But that has nothing to do with my question.  Just some background. My question has to do with a properly welded butt joint.  After I finish welding a section I start grinding off the excess weld.  I had always thought that the 2 pieces of metal are supposed to be fused together.  However to my dismay the original seam reappears after a little griding.  So I lay down some more weld, even burning through in a couple places, thinking I've got plenty on there now. I grind it back down only to reveal the seam again.So my question is, on a butt weld are the 2 pieces supposed to fuse together so you don't see the seam, or are you supposed to leave a little hump of weld and then smooth it out with body filler?Thanks.
Reply:Whataqestion!Butt welds are tough.  You are working with some thin plate.  You do have the right machine to do the job except for the taps.When I mig weld things like that, I weld the two pieces together in a back and forth motion pausing long enough to keep a good puddle.  While you are on one side, the other side is cooling.  Fitup is important.  A lap weld is much easier.   Since all you  get is A or B, you can adjust the wire speed to fine tune it.   If I were welding floor pans in, I wouldn't grind the welds unless the customer asked for it.show us pictures and ask away I have to fix a rocker panel on a ford next weekend.  I'll take pics.  I'll be using an SP100 with .023 wire and C/25.DavidReal world weldin.  When I grow up I want to be a tig weldor.
Reply:Originally Posted by RaindemHi. Totally newbie question so please bear with me.I'm butt welding a floorpan replacement using a Lincoln weldpak 100, with .23 wire and C25 gas.  I started out with volts on A and wire speed at 2.5, but I wasn't getting any penetration. The weld would just ball up on the surface. So I increased volts to B and got penetration on the new part, but started blowing through the old part. Finally got it to stick by going back to A and using a copper backing strip which lets me move slower.But that has nothing to do with my question.  Just some background. My question has to do with a properly welded butt joint.  After I finish welding a section I start grinding off the excess weld.  I had always thought that the 2 pieces of metal are supposed to be fused together.  However to my dismay the original seam reappears after a little griding.  So I lay down some more weld, even burning through in a couple places, thinking I've got plenty on there now. I grind it back down only to reveal the seam again.So my question is, on a butt weld are the 2 pieces supposed to fuse together so you don't see the seam, or are you supposed to leave a little hump of weld and then smooth it out with body filler?Thanks.
Reply:Grind it if needed, but leave a little hump and fill with body filler if needed.  On a floor pan that will be covered by carpet (?), probly not necessary to do any grinding or filling.  Chopper5 is right- tack, pause, tack, pause...etc.MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op
Reply:I'm wondering if you have the polarity set wrong. For solid wire you should have the polarity set electrode positive.
Reply:Today I welded some 1/8" with my SP100.  got pics.  Settings were J8, .023 wire C/25 gas.Back sideThis could be ground flush.DavidLast edited by David R; 01-22-2008 at 06:06 PM.Real world weldin.  When I grow up I want to be a tig weldor.
Reply:Chopper:  wire = .23, gas = C25, metal is shiny cleanDan: Polarity is correct.  I practiced some beads on the old floorpan (the part I cut out).  They weren't as nice as Davids but they weren't too bad.David: So if those welds were ground flush, would you be able to see the original seam?
Reply:Originally Posted by RaindemDavid: So if those welds were ground flush, would you be able to see the original seam?
Reply:Use more heat and don't try to run a "bead" per se.  Just do a series of overlapping spot welds on material that thin.  You'll save a lot of headaches that way.
Reply:Originally Posted by Raindem   David: So if those welds were ground flush, would you be able to see the original seam?
Reply:Thanks for the pics David. I'm obviously not getting enough penetration. The back of my piece doesn't show any weld, just some heat marks.Time to go back to the practice piece. I'll leave the Volts on A and turn down the wire speed a bit.  Also, my gas was set at 12 cfm.  Is there anything to be gained by increasing it to 15-20?Thanks
Reply:If you get porosity with the proper gun angle and stick out, turn it up.  Otherwise leave it.YOU CAN DO IT!DavidReal world weldin.  When I grow up I want to be a tig weldor.
Reply:Originally Posted by RaindemThanks for the pics David. I'm obviously not getting enough penetration. The back of my piece doesn't show any weld, just some heat marks.Time to go back to the practice piece. I'll leave the Volts on A and turn down the wire speed a bit.  Also, my gas was set at 12 cfm.  Is there anything to be gained by increasing it to 15-20?Thanks