The classic 4130 chromoly steel welded structure has always been one of the most common building mediums to work with on experimental aircraft. This type of construction lends itself to a multitude of different types of applications and renders one of the highest strength to weight ratio manufacturing techniques, especially when it comes to fuselage assemblies. The welding of steel tube assemblies is a process that can be readily learned by just about anyone. And with current welding technologies like the TIG (tungsten inert gas) welder now coming down in price and becoming readily available to the average builder, precision welded aircraft subassemblies are no longer relegated to the professionals. (Figure: 1) Although this article is not a treatise on welding techniques, it is the primary answer to “How do I become a good welder?”
Becoming a good welder requires that you learn the principles of welding. Our recommendation, especially if you’re brand new to welding, is that you simply engage in a training program. Often a community college class is your most cost-effective method of learning the skills you need. And then, of course, practice is the key to becoming proficient. As you begin the process of welding, one of the first things that you will identify is that it becomes very easy to make beautiful looking welds if everything is set up properly. Good equipment, good environment, clean materials, and, equally as important, a proper fit of the pieces of material which you’re welding together. This has always been one of the most frustrating parts of making a 4130 chromoly steel fuselage assembly. Typically, when we are working off of a set of plans, we are taking a piece of 4130 tubing, cut it to length, and then grinding each end to precisely interface with the adjacent tube. We refer to this as “coping”. This process is usually a lengthy process of trial and error. We place the tube in position, then mark it, and then grind the end of the tube, refit the tube in place, check it, market and duplicate the process all over again until we have a proper fit. The process can be tedious, but if you have patience and a good eye for spatial orientation, with a little bit of practice, you can become pretty good at the process. All this being said, I’ve never met anyone who has welded a steel fuselage frame who has not come across the issue of fitting the tube and ending up with a fairly large gap on accident. If you’ve ever tried to close up that 1/4-inch gap by welding, you know that the end result isn’t going to be all that pretty. Those really pretty welds, that we all admire, are primarily a result of having two pieces of metal properly prepped and with a very nice clean consistent fit against each other. The welding bead flows very seamlessly and consistently because of this close contact. Producing a beautiful weld with these conditions is a no-brainer.