Vertical Jigging
Jump Run Enterprises LLC

4130 Steel Tube Airframe Construction Video
Jigging in Space:  "Many aircraft are built with flat sides.  On some designs however, where the width of the airframe is different at the top than the bottom, it’s necessary to do what’s referred to as “building in space”.
Vertical Jig Board:  "Transfer the layout to the board, and devise a method to secure it to the table, the airframe, or both.  Usually, you can get a good start on this by utilizing the same jig blocks used on the table or your 2X4’s used to stand up the sides."
Bending Tubing:  "In some cases you can use the methods mentioned earlier, when we covered bending the lower longeron, or bending the sides of the airframe into the tail post.
Regardless of the method used, you should always make your initial piece of tube too long, and once the bend is complete, match the sweet spot and trim off the excess."