Welding holes - answer to PM from Ken
Ken, your PM ddn't give me an e-mail address to respone to so I will respond here in hopes you will read it.
You can spot weld up holes with a tig up to aboout 1/4". Larger than that and you shoould cut a patch and weld it in.
The copper back up plate is held behind the hole while you weld. It insures a flat surface on the inside. The beauty is that the weld won't penetrate the copper so onnce you are finished welding, just pull the copper away and it is ready to use over and over.
Any time you weld sheet metal, you stand the chance of warpage. When welding with a MIG (solid wire and CO2/Argon - don't try self fluxed wire feed), just do quick spot welds, let it cool and then do another spot, and so on 'til the hole or joint is done. Goal is to get a fully welded joint without any bluing of the metal around it. Takes a little practice but when you get it right, you can do some really great sheet metal welding with zero warpage.