"It isn't certifiable until the welder is certified..."
An IA is supposed to be able to determine if a weld is aceptable, the welder being certified is just -your- means of doing that.
If there is nothing in the aircraft maintenance manual regarding welded repairs (methods, certified welder, etc), or there is no maintenace manual (as is the case for many airplanes constructed of steel tube, then people only have to use FAR 43 and AC43.13 "acceptable methods and practices".
Unless the weld was made with MIG, I doubt that any weld that was done in accordance with AC43.13, was pre-heated and stress relieved, and adheres to a proper visual inspection is going to fail below its design load (assuming is was engineered properly). 'certified' welder or not.
Not that MIG isnt certifiable, from what I have read, its too easy for a non-pro to make a good looking weld which isn't actually strong. With gas, if you make a cold weld (bad) that looks good, its probably a miracle.
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For the original poster;
If all you want to weld is one job, leave it to a pro. If you plan on doing more extensive welding; start with gas, get a lightweight torch like the harris 15, go around during "clean-up" week and grab up some discarded bicycles (many of which are made of expensive 4130) and start practicing.
Thats probably the cheapest way to decide if its something you want to do, baring borrowing rig from a neighbor.
tinmantech.com has good info.
the meco midget is a good little torch, but you might need a slightly bigger backup torch (like the harris 15) for welding large clusters.
