Gentlemen, I apologize if this is the wrong place to post this so please direct me to the appropriate thread if I have erred. I need to cut the "birds mouth" out of the domed end of my propane tank to mate the firebox I just built to it. I have a plasma cutter, cutting wheels, levels, and squares. I just want to make sure that my cuts are even, level, and square. I need advice on how to lay this out properly and also maybe a few hints on how to put a makeshift guide so that when I cut it with the plasma that my cuts are as straight as possible. I'm a newbie to metal fabrication and have tried to do as much and learn as much on my own as possible. Any help would be greatly appreciated.