MIG penetration near tack welds

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Parameters: 12 gauge CRS, square groove butt-weld with a 0.060"-0.070" gap. Tacked both ends, then started on center of tack and welded straight across (no weave etc) with 0.030" wire with a push angle at 19V 310 ipm (120-130A). I think my push angle was around 30 degrees. Very little warpage and joint penetration is good, except immediately after tacks. I've seen a similar problem if I tack in the middle, that immediately after the tack, joint penetration is not complete. Even grinding down the tacks I sometimes have the same issue, I think the tack is blocking the arc because of the gun angle.  Is there something simple I'm not doing correctly that would prevent this? Should I be using a drag motion?  The upper weld was started on the right, the lower on the left. Thanks.
Reply:Hello Jieve, you said that you ground your tacks, but did you taper the starts and stops(ends) of the tacks? In order to properly tie in and sometimes consume a tack you should experiment a bit with a thin disc and "tapering" the ends of the tacks. This can lead to the ability to weld over, or up to, the tack and not experience a "hole" or lack of fill on the backside at the ends of the tacks. Good luck and regards, Allanaevald
Reply:It's referred to as "feathering" your tacks. Get an .045" cutting wheel in your grinder, grind the ends of your tack until they are a razor edge. A thin edge on your tack will let you burn in (through) as you weld up to, and past your tack.IAMAW Local 330Airco 300 AC/DC HeliwelderAirco Dip-Pak 200 with Profax spool gunPowr-Kraft AC225Everlast PowerArc 200stBuffalo Forge No.21 drill pressSpeedglas 9100xxAirco, Oxweld, Purox, Victor torchesLincoln Ranger 8
Reply:Thanks for the responses. I was always just grinding the tacks flush, not feathering the edges. Will give that a shot. Thanks for the tips, exactly what i was looking for.