A step-by-step intro to gas welding of aluminum continues, plus basic tips on repair.

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Last aluminum welding article, we introduced you to gas welding of aluminum; I specifically, with hydrogen as the fuel (acetylene is commonly used for welding 4130 chrome-moly steel) and oxygen as the “supercharger,” which aids in hotter, more controlled burning.

Mig and Tig welding are more commonly used today for aluminum, but at one time gas welding was the primary method; it’s relatively simple once you’ve mastered the technique, much less expensive than other forms and. when done properly, just as safe structurally. The only drawback is that the entire piece to be welded must be heated.

Since aluminum “captures” heat rapidly, larger pieces dissipate the heat before the proper welding temperature can be reached. But most of the homebuilder’s tasks will involve smaller pieces. Our instructor is Steve Neander, EAA Workshop volunteer and co-owner of Crane Service Inc. of Midlothian, III.

Our task is to join two pieces of aluminum, as with the halves of a fuel tank or two landing gear parts. Unlike 4130 chrome-moly steel, no gap between the two pieces is necessary because aluminum heats all the way through the piece so that full penetration is not a potential problem.

Our torch is lit, goggles are on and rods are fluxed, so let’s hit it. Good gas welding of aluminum is accomplished by establishing the proper rhythm, which may vary from job to job depending on the particular style of the builder.

Heat the pieces to be welded, called the “parent” metal, by bathing them in flame. Then, aim the flame Into the crack to be filled, in the direction you will be welding, while holding the torch at roughly 45 degrees from vertical. Keep the heat at the inception of the weld until a puddle forms.

Remember, the puddle will be slightly gray in color, look like it has wrinkles and begin to sink with a slight concave depression. That’s when It’s ready to fall through for lack of material, and that’s when you want to add the fluxed rod.

Hold the rod at approximately 45 degrees from the other direction, directly in line with the crack, and dip it right down into the puddle. Now comes the tricky part. As the rod flows into the puddle, raise the flame up and away from the puddle.

Here you must keep the rod in line with the unwelded crack so that the flame does not bathe the crack prematurely. After lifting the flame from the puddle, put it right back down again, achieve the puddle, which will be a little further along now, and feed In more rod as needed.

When it fills, run the flame up the rod and back down into the puddle, and work it along with that steady up-and-down, up-and-down rhythm, using the flame to control the heat. Remember, you can’t see the puddle unless you have on the pink didymium goggles, and the puddle is all-important to a successful weld.

Obviously, the rhythm of your welding will depend on the thickness of your metal, the heat of your torch and your own style. The only law here is that a good, steady rhythm is essential for a clean, uniform weld.

When reaching the end of the weld, If you’re running into a previous weld as in the photos above, continue your rhythm on, into and through that weld, maintain your puddle, fill with the rod, remove the rod and the heat, and you’ve done it.

You now have the basic information to do your own aluminum welding. What about making repairs to torn or broken aluminum pieces? No problem. You’ll use the same techniques as above, with some minor modifications.

Above

• This aluminum bracing tube from an ultralight was originally squashed and drilled. Eventually, it cracked at both corners, as shown above. The danger you’ll face with this kind of repair is overheating the metal. As shown at the top of the piece, you’ll have to fill with excess material before reinforcing the piece on the other side (hidden from view).

• Since the cracked area is thin, and the material makes a kind of corner, it is more susceptible to “fall through,” or melting away. You’ll want to reset your torch to a lower temperature. Achieve this by reducing the line pressure on both the oxygen and hydrogen lines.

  As a ballpark example, if the circle of flame you made on the firebrick before was roughly the size of a quarter, you ‘II be looking for a circle closer to the size of a nickel. Once the lower-temperature flame is set, you can heat the metal until achieving the puddle. Remember, aluminum welds best at close to its melting point.

• Heat the piece to achieve your puddle. Be careful not to let the puddle sink before you add rod, or you ‘II lose vital material and the repair will be more difficult and sloppy. Notice how the flux flows away from the weld.

• Here’s what the left side looks like after some heating, and after some material has been added. The crack on the right has already been filled. Note the dried flux near the other now-filled weld.

• Keep the area hot and allow the material to flow into the puddle; fill the crack completely.

Above

• When you’ve got plenty of material in, withdraw the rod and then the flame. Now you have the basis for finishing the repair.

• To fill in and completely reinforce the other side of the piece, start with the beefed-up corner you’ve just finished, then turn the piece over while maintaining heating.

• Turn the piece on its side to make the weld ‘s journey from one crack to the other smooth and continuous.

• On the other side, you’ll have worked from one filled crack into and through the other. As with joining two pieces, you’ll want to achieve a good moving puddle and keep your rhythm smooth and steady.

• On this. the original side, with final heating and filling completed and once the weld is properly done, there is no reason you can’t file, machine, cut or in any other way work the material as if it were one solid piece of aluminum.

  Once your aluminum welding is done, be sure to wash the flux off of the parts completely with hot water. Wipe it off with your hands, or, as with an enclosed part like a fuel tank, fill with hot water and agitate thoroughly. Flux is highly corrosive, so you must never leave it on the metal. Since it also water soluble, hot water is all you need for cleanup.

That’s all there is to it. No text and photo sequence, though, however thorough, will give you the skill. So practice is essential. The purpose here, as with our entire Oshkosh Workshop series, is to give you the confidence to try it out. We’re sure you’ll be surprised at how unmystical the complete process really is.