As a typical homebuilder (is there such a thing?) who wanted to build as well as fly his own airplane, I selected as my first project the Fly Baby, a basic, wood-and-fabric beauty designed in the 1960s by Pete Bowers (completely unaware of the oxy-acetylene gas welding requirements). Everything went smoothly until I reached the page in the construction manual where Bowers made this caveat about welding some of the fittings: "If you're unsure of your welding skills, get it done professionally." I thought to myself, "This is supposed to be a learning experience, so I'll learn how to do it myself." I scraped together all the necessary gas welding tools of the trade and - because there were no "teach-yourself-how-to-weld" books in print at the time — picked up the skills the old-fashioned way: I earned them.
You really can learn how to gas weld. All it takes is practice, practice and more practice. As for the equipment - learn about the parts of a gas welding torch, you'll need a gas welding rig including oxygen and acetylene tanks, regulators, torch tips (numbers 0, 3 and 5), welding rod (1/16- and 3/32-inch mild steel), igniter, wire brush, tip cleaner, welding goggles or glasses, protective clothing, welding gloves, plenty of steel scrap (0.060 to 0.120-inch-thick for practice), holding clamps and a work area.
I was lucky enough to borrow a small gas welding torch rig from a neighbor. The local welding supply store outfitted me with the rest of the equipment I needed. The steel scrap came from a local welder's scrap bin, where I also found several thick metal plates that could be used as a work area.
Before I go any further, I have to mention something very important in regard to welding: safety. Working with two potentially explosive pressurized cylinders near an open flame with a temperature close to 2800°F, safety considerations should be fairly important to you. If you use the proper procedures and a bit of common sense, you should have no problems. It can't be too dangerous. After all, there are plenty of old welders around.
To keep it that way, always transport oxygen and acetylene tanks with their caps on, ensure that gauges are set at the right pressure, remove all flammable debris from your work area, wear protective clothing (long sleeves and welding gloves), and always wear eye protection. Staring at a flame as bright as the sun without some sort of eye protection is insane, but I've seen the occasional "Mister Macho" actually do it. Trust me —wear goggles!
Okay, now you're ready to weld. First, clamp a couple of 1-inch strips of 0.060 steel together in the shape of a T. I recommend using a No. 3 tip and the 3/32 - inch rod. HOW TO LIGHT A GAS WELDING TORCH: Turn on the gas (the red hose) just enough to hear it hissing and light it with the igniter (matches are a definite no-no). With the gas lit, open the valve until you get about a 2-inch flame, then feed in some oxygen until the flame turns blue.
There's a trick to getting the right oxygen-acetylene mixture. By adjusting the amount of oxygen, you can create three types of flame: a carbonizing flame (not enough oxygen), an oxidizing flame (too much oxygen), and a neutral flame (just enough oxygen). The best flame for welding aircraft-quality chromoly steel is a slightly carbonizing flame.
You can adjust the torch to a neutral flame by making the cone of light-blue flame disappear. Backing off the oxygen a bit and forming the light-blue cone again adds a touch of carbon to the weld (Figure 1). Hold the torch in one hand (the right hand, in my case) and some rod in the other. Work from right to left and remember to wear gloves! Also, try to steady your arms against the work table or your chest so you don't shake or tire too quickly.
ABOVE: Figure 1. Torch-tip flames. A carbonizing flame has inadequate oxygen, while an oxidizing flame has too much, and a neutral flame hasjust enough.
Even with the best gas welding torch, the technique is the same - Heat the metal evenly so that it glows reddish-orange. When it does, concentrate the tip of the flame where you want to start the weld. The idea is to form a small puddle of melted steel on both sides of the seam where you will be feeding the welding rod. Remember, this is oxy-acetylene gas welding, not soldering - the steel must also melt to join properly.
On my first few practice welds with the portable gas welding torch. I made the mistake of not heating the metal enough to create a good weld. All I did was melt some rod onto the metal; in other words, I soldered them together instead of welding them. The other extreme is heating the metal so much it melts through.
Learning how to hit the middle ground between these two extremes takes - what else, practice - which is the purpose of these exercises. Initially, your welds will probably look awful, but keep at it and you'll get better. I did. The perfect weld will have a rounded, slightly raised appearance (Figure 2) and will be stronger than the pieces you are joining, obtaining proficiency with your aircraft gas welding torch is only a matter of time.
ABOVE: Figure 2. With a basic T-type weld, heat both pieces of metal and apply the welding rod slowly from right to left, creating a seam that is rounded and slightly raised.
Something you may experience during your first practice session is a popping (more like exploding) of the flame at the tip of the torch. This is caused by using too little oxygen and acetylene, which causes the two to ignite inside the tip. It's an easy problem to solve with some gas welding torch tips - simply increase the amount of gas and oxygen proportionately.
Once you feel confident making basic T-type welds, you can move on to other types of gas welds, one of which is joining two pieces of different thicknesses - a piece of .030 tubing and a .060 flange, for example. Heat the flange before you heat the tubing. Another trick is to put a clamp on the tube to act as a heat sink, absorbing and dissipating some of the heat to keep it from melting through.
Another problem you might encounter with gas cutting torch and welding torch use is warping of the pieces you're working on, which often happens to metal tubing when one side is heated by welding, causing it to expand only on that side. You can prevent this by using a jig and clamps to hold everything in place where possible, and tack-welding the pieces in place. After they cool, reheat the entire tube evenly so it will cool evenly, which also relieves stress around the joint.
Obviously, this isn't everything there is to know about the fine art of gas welding torches, but it's enough to get you over the initial fear that it's too much to handle without experience...perhaps it's enough to get you started. The key to success is practicing on scraps until you've mastered the basic technique. It's a way to make mistakes that you can afford while learning from them in the process.