well that video is just about amazing.
when the two guys are forge welding the wound-up tube, whats going on during the herky-jerky motion with the tube after it comes out of the fire, but before they start beatin on it ?
You mean when are whacking it on the side of the anvil? That's called jump welding. It is actually when the weld in the coils is made on the bore edges of the billet. The hammering is at first surface welding then smoothing and drawing length/thickness. You'd be surprised how effective a jump weld is. Can help you make several joints you couldn't by just hammering
John
