Welding Techniques
Jump Run Enterprises, LLC

4130 Steel Tube Airframe Construction Video
Purchasing Practice Tubing:  "Several aircraft materials suppliers also offer a “Bargain Bag” of assorted tubing pieces.  I would suggest looking at your plans, and purchasing several feet of the actual tubing you will be using. The bargain bags typically include allot of very thick walled tubing that is not very useful for practice."  
Practice, Practice, Practice:  "Regardless of which way you decide to weld, (TIG or Gas) I would highly recommend you obtain the necessary training, and practice until you are proficient.  Also, have an experienced welder inspect your practice welds as you progress.  This will ensure you are on the right track, and aren't practicing bad techniques."
Setting Pressures On Your Gas Torch:  "One tip on Gas welding, that isn't talked about much, is the proper way to set the pressures on the gas torch.  The following technique works for any torch and any combination of tip sizes."
Welding Terms:  "Stress relieving, and torch normalizing, are terms that are commonly used to describe the process of post heating your welded joints.  The problem with trying to define these terms is that reliable sources will disagree about all of these things."
Sharpening Tungsten:   "To prepare tungsten for use, put it in your cordless screw driver and taper the end on your belt sander.  Make the taper 1/4" long on a 1/16" tungsten, and have the entire tapered part beyond the end of the pink cup."

TIG vs. Gas  "The two most popular methods to tack and weld your airframe are Tungsten Inert Gas, or TIG, and Oxy/Acetylene, also referred to as Gas welding.  Both methods have ardent proponents, and I will not even attempt to get into which is better than the other. 
I personally choose to TIG weld wherever possible.  TIG is the more modern of the two techniques, and allows for very fine control of heat and the weld puddle.  
Gas is the more traditional method of welding.  Thousands of aircraft which were welded using gas are still flying, and its still a very acceptable method to weld your airframe."