The advice given is correct but as I don't know your experience level I will make the presumption that you don't have a lot of experience or you wouldn't ask the question, not trying to tread on any toes but this is not a job for a beginner. It will pay you big time to do a TAFE night course in Panel beating. It is great fun and all participants say they really get a lot out of it and then plan to redo the work they attempted prior to doing the course.
What you will learn is that the panel will shrink where it is seem welded and will need massaging to stretch it back out. This is the reason plenishing hammers have a slight dome to them to create a high pressure point and then the metal is trapped between the hammer and the dolly and this squashes the metal and stretches it back out.
Generally it is better to use an oxy or tig as the mig tends to harden the metal and make it difficult to dress up. The mig is by far the best for the plug welds. The other thing that many folks don't know is that when you weld the seam up try to have the weld slightly above the surface. That gives some material to work with when you sand that down. Plus the most important long term issue will be rust.
If you leave a recessed line of weld it will be close to impossible to clean up as far as surface prep. That is cleaning the metal so that all the oxides are removed, near impossible if the weld area look like craters on the moon. Rust loves to start in these areas. Hopefully this info is of help to you, if not others planning restorations.
There is one other little trick I like for welding, it is the use of a copper backing plate or if this is not applicable the use of a product called Solar Flux. What it does is really help the solidity of the weld by stopping oxidation at the back of the weld. Think of it like back purging which is used when the weld on a pipe has to be high quality like on a set of race headers. It is quite cheap to buy and will last you many years.
For those of you who may not be sure of what I am talking about. Picture this, when you weld with say a TIG the Argon protects the top of the weld but if oxygen gets to the back of the weld it will be highly compromised because of the burning of the metal, known as oxidization.
Edited by user Wednesday, 18 January 2012 4:34:00 AM(UTC)
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