Dan has some experience with ox-acetylene welding. He purchased a new small tip. We had purchased a bunch of left over drops of 4130 tubing from Wicks to practice on. I cannot find this item on their website right now. Dan tells me that the thicker tubing is easier to weld. The thin wall sizes are tricky since you can melt a hole in the tube if not paying attention.
One end of some of the control rods have a Grade 8 bolt welded into the tube. The tube is cut so tabs can rest on the hex head faces.