How is it that a weld can provide full strength if it does not penetrate the full thickness of the metal?
I learned the answer to that one right here on this NG. I'm not real clear on how to answer it but I suppose it is partly intuitive. I welcome the clearer thinkers amongst us to join in.
Melting metal and splattering it on top the joint of two pieces of metal is not welding, but once you have both the work and filler to liquid state they marry. Spot welds and stud welds are good examples of next to nil penetration yet they still work and are used widely. If the work truly reaches melting temperature, penetration is not an issue and happens on it's own (IMO).
I think here is the catch. Electric arc welding takes the work "spot" up to temp rather quickly. The work metal has the ability to absorb that heat quickly so the machine must be able to surpass the heat sinking and actually melt the filler and work "spot". The larger the work piece and electrode, the more energy it takes to get them both melted at the same time. The puddle will tell you when the parent metal is melting. You should see something like a glittering spot of mercury. The color will vary depending on your lens. If the electrode has flux it may hide the molten metal a bit but you should still be able to see it at the front part of your run. It will be the brightest part. One of the best tips I've learned here is to pay close attention to the "puddle". You will not have to do destruction testing once you get used to how good puddles look. You will know before you raise your hood and the metal cools if the weld will hold or not.
With your 3/16 angle, I would just leave a 1/16-1/8 gap and weld it up with .023 solid wire and try for a single pass. No veeing or other pretty stuff other than grinding the rust off and maybe doing the other side for practice. If you are new to MIG, give yourself at least a two pound roll to play with on any metal you can scrounge in the trash etc. Keep a few notes especially about the stuff you do right and how you think you did it.
So to sum it up, it all depends on you and your machine being able to make a good liquid puddle on the size piece you plan to weld. I'm not talking the whole joint, but just the spot where the electrode is working at the moment. Factors to juggle are travel speed & eccentric motion, electrode angle & stickout, machine settings, indoors or out, and maybe more. Smaller MIG wire generally makes a smaller puddle so less work for the machine at any given moment in time. Of course you will need to come back with multiple beads to fill larger areas.
Thanks for the chance to ramble....
Zorro