Help with welding wire size

[Harley55]

I have a Millermatic 172, running Argon/co2 mix (75/25 I believe). I will be welding all 3/16 material on my next project (utility trailer). I currently have (.30) wire in the welder. For this project would I be better served to use (.35) wire. I have seen some charts and they seem to recommend this size wire for this thickness steel. Looking at the chart on the inside of the welder, it indicates that I drop to a 3 for voltage and 55 for wire speed (4/70) if I were to use the (.30) wire). Why the significant drop in voltage and would I be assured of better penetration if I increased it to 4? As an amateur, I am nervous about the strength of the welds. The steel I will be using is new with mill scale on it, which I will grind off.

Any suggestions would be greatly appreciated.

[aametalmaster]

I would stick with the .030. thats my everything size wire in my MM185...Bob

[leon phelps]

Too many variables to be welding right out of the book. Travel speed, the deposition needed and the penetration for strength can not be right from the book. Best bet is to test with a small piece and then test the weld strength on your own. I would guess .030 for this light metal.

[Tom C]

Harley 55

JC..........Don't be nervous as Ho in Church ?............... The gas mix is fine ........ actually I prefer 88 %- 12 % when I do short -arc ( little splatter and better sheilding ans peneration ) .............. a little weld does a long ways ............ notice I said a liitle weld goes a long ways............ short -arc produces a hard brittle weld but for anything under 1/4' ,,,,,,NP.........don't worry about the strengh........You Ok.........more then OK........... Kid Knows

[tnjind]

I would practice on steel first. When you weld enough steel then You will feel confident enough to answer your questions. Soon enough you will not even use the door charts. I think 0.30 is an all around good size wire for your machine.

Just my thoughts, don't seem to be worth much these days.