Because the stand currently isn’t clamped down or welded to the table as he usually would, he is welding short sections on one side, then the other of the structure. He welds 3 – 4 inch sections at a time, then skips a foot-long section, then welds 3 – 4 more inches.
Each time, he switches back and forth between the sides of the stand as he welds to counter the inevitable warpage that happens when welding metal. Then he comes back, splits the difference in the open foot-long section, welds, goes to the other side, welds there, then goes back and forth.
When this top of the stand is completely welded, he’ll flip over the structure and weld the other side the same way, first welding the metal on one side, then on the other to pull it back from where it has moved during welding.
Kevin then explains how he has actually used the warpage to shape a sculpture called Genome Project. The sculpture started almost flat, but he intentionally started welding in one spot, welded up, then went to the opposite side and welded down, going back and forth to achieve a sweeping shape.
But what about the nice long welds you see, including some on his own sculpture? Kevin explains he tied together all the welds to get what looks like a single long weld by filling in the sections between his short, spaced welds. He explains that you don’t run over the short welds, but tie the welds together, which he covers in another video.