I'm substituting this week as a teacher and gonna start a guy on his 3g in mig. He's using bare wire with 75/25 and an open root/carbon steel. I did this test awhile ago and was told the root opening was the same size as the wire? Is this correct? I tried it and ended up putting a 1/16th root opening or so on the plate, it just did not work out for me with that .035 root opening. Anyhow, I know that for mig they want you to use a 30 degree angle, 60 included but in the books we have at the school they all show using a backing plate with 1/8th gap. What does AWS say about an open root gap with mig? I don't want to give the guy shoddy info and would like to know exactly what AWS says for future reference. Any help would be appreciated and many thanks!
Shawn