Plug welding with MIG questions.

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Hi,I need to duplicate spot welds on a car that I am restoring. What size hole should I drill in the panel that I am welding, also should I hold the welding tip at an angle?
Reply:Hold your nozzle straight in, 90 degrees in all directions, when doing spot welds.   Drill your hole slightly smaller than you want the finished to be.MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op
Reply:On my old Ford the plug welds were 5/16". Making the holes with a hand drill can be difficult due to the flexing of the sheet metal (especially if holes needed on edges). A drill press is a better choice for drilling. One of these punches from HF works well too:http://www.harborfreight.com/cpi/cta...emnumber=91510Lincoln 140CMillermatic 211Thermal Dynamics 52
Reply:Ok, so I'm plug welding my trunk floor and the weld is only sticking to the base metal. I coated both metals with zinc rich spray coating by NAPA. I assumed it was ok to use for welding, I cant think of any other reason my welds are not working. Ive tried adjusting the voltage and speed. I am welding 18 ga with a miller 130 mig gas mix. Is this coating my problem?
Reply:It's the zinc spray you used.  You may need to remove the coating from the areas you want to weld.
Reply:chrisd6875  -  Are you replicating spot-welds [typical of auto body] or MIG-plug welds.  If the spot-weld look is what you want, you can only faux the look with TIG.  Please note the affect and the gauge of the section.   OPUS
Reply:I don't care too much about faking the spot weld look. What I'm concerned with is getting a good weld and protecting it from rust. The plug weld look is close enough for me once I gring down the weld from the welded side, It will be fine.I've seen posts about people using zinc weld-thru primers. I would hate to finish the whole car and then find out I should have  used this weld-thru stuff. I'm just not sure if its the thing to do.I feel like I'm sacrificing a good weld for a protected weld.
Reply:In addition to probably poisoning yourself in the process.Have you read up on zinc fumes?Syncro 250 DX Dynasty 200 DXMM 251 w/30A SG XMT 304 w/714 Feeder & Optima PulserHH187Dialarc 250 AC/DCHypertherm PM 1250Smith, Harris, Victor O/ASmith and Thermco Gas MixersAccess to a full fab shop with CNC Plasma, Water Jet, etc.
Reply:If you're going to be welding on galvanized metal or spray galvanized metal and not grind it off, then ditch the solid mig wire and shielding gas and use fluxcore wire.  Solid wire and gas with galvanized results in porosity.  The flux in the fluxcore wire allows welding on galvanized metal without the porosity problem.Also, wear a respirator mask and keep your head on the upwind side of the weld.MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op