Ive been doing an old car up but am having trouble with plug welds ,some are good and strong but some just seem to fill the hole but dont penetrate the bottom sheet..I drill a 6mm hole and turn the welder power up like i say it seems to be ok sometimes.I think it could be that the wire is earthing on edge of hole rather than lower sheet?Also can you plug weld upwards or is that no good.Im going to up the size of hole to 7.5mm like it says in tutorial.How about the gas could this be at fault?would to much cool the weld to much?All other welding is good just plug welds which i think may be due to hole size...im not sure...