He has two pieces of 16 gauge mild steel clamped down to his 1″ thick welding table, with two pieces of 1″ square tubing between the clamps and the metal, running the length of the steel. This alone should help keep the weld from warping.
The two pieces of steel tubing str close to the weld with enough room between them to get his torch and filler rod in between them to weld.
Kevin fires up his Everlast PowerTIG 255EXT at 80 amps and puts a tack weld on each end and in the middle of the metal. Then he welds half of the length without pulse, and half of it with pulse.
He sets pulse time at 50%, pulse amperage at 39% (of 80 amps), and pulse frequency at 3 herz.
When Kevin takes off the clamps, you can see that the section welded without pulse is not as flat as the section welded with pulse.
So if you have a machine with pulse, using it is a good way to reduce heat distortion.
Kevin is going back to work, but you might want to stick around another moment and see him forget, well, everything ….