I'm new to this welding stuff. I've heard that metal shrinks where it's welded. I'm trying to make a square metal frame. I'm clamping it and even tacking it to the work surface before welding. After I'm done, I pull the clamps and grind the tacks and that's where things go bad. It's no longer square. How can I prevent this or compensate for it? Do I hammer the welds before letting the clamps loose? Should I wait longer before pulling the clamps? Should I do short welds and wait between them instead of running a complete bead? Any ideas? By the way, this is 16 guage, 1" square tube. Thanks, Eric M.