OK isiahstites here it is the "hammer and torch" method of fitting tubine. First a couple of words of advice: Don't uses this method with 4130 tubing. Once you have it cut with the torch it is a bitch to file. It works great on heavy wall mild steel tubing or pipe. This method is not as nice or clean or easy as using a joint saw, the quality of the fit is directly proportional to the amount of work you put into it. More experience will get it done faster and better.
Tools required: Torch with good cutting head. Gloves, good shades or goggles, a good quality large radius 1/2 round file, floor mounted grinder, disk or belt, mine is a 12 inch disc.
This proceedure is to make a tube joint that is a 90 degree joint. I sometimes will mark the tube with calk to somewhat outline the cut that I am looking for, next you hold the torch at the center of the tube back from the end where you made your mark, angle the torch approx 45 degrees (see picture). Once the torch has made its puddle you hit the ox and you will blow a hole in the tube at an angle, now move the torch in a straight line back and forth across the tube. If you have your ox set at around 35-40 psi the torch will cut completely to the end of the tube. ( see pics again). Turn the tube 180 degrees and do the same for the other side. Now you have the big pieces out and the real work begins, using the disc grinder and the file remove any material that will prevent a good fit up between the tubes. (In other words this is were the work come in!) I did this fit up in about 5 minutes. Tubing is 1-3/4 dia x .095 wall.
Just to show the correct way to install a diagonal tube for proper "excentricity" I cut a second tube to match into the joint at 45 degrees. Again it took about 5 minutes to cut, grind and file this joint so that it could be welded. You can see that the diagonal is welded to each leg of the 90 degree joint and the center lines of each tube would cross at the same place. This is strongest, and stiffest joint design you can use for diagonals. It is a little more work but worth it for the increase strength.
I will do a couple of more post to get all of the pics.
Rex