I was taught by Duane Korn from H&L Metals on Signal Hill, who did all of my bending, how to make tube joints using a torch. I would not recommend it with 4130 but on mild steel it works great. You need to calculate the depth of the cut into the tube and then lay the cutting torch at the angle that you need and start with the torch in the middle of the tube. Once the metal starts to melt and you have a small puddle, hit the ox and stroke the torch to cut one side and then, keeping the torch at the same angle to the tube, stroke back to cut the other side of the notch. You will need to have the ox high enough to cut the depth you want the joint to be. A little clean up on the big disc grinder and you are ready to go. I know it sounds kind of crude but like everything if you work at it you can get pretty good. I have built probably 10 cages most of them for sports cars, so they are pretty complex and have used this method for them all.
That being said I think I'll buy one of the JIG a Joints for the next one just to try it.
Rex