Happens alot. Not a big deal. Grind a "V" shape on the bottom and top side on both pieces. Clamp both pieces down flat. Weld the top side first with short passes if it is a large break. Let it cool completely and slowly. Flip over and do the same on the other side and then use a surface conditioning disc to knock the weld down. Check with a straight edge. Dose not need to be perfect but real close. Good luck.