Welding Aluminum By James Goss      There is one area in model airplane building that most of us is lacking when it comes to equipment needs. When it is time to modify or repair our mufflers and landing gear we are limited as to what we can do. It is sad that we must buy a complete new muffler simply because part of it has broken off in a hard landing. For example you have spent $100 for a Pitts muffler and the down pipes broke off in a nose over during landing. The pipes are still in good shape they just popped out. Your choice is to take it to a welding shop or buy a new muffler. It would be nice if you could repair it in your shop to save time and money. Some of us would like to be able to design and build our own mufflers as well, especially for large gas engines. It would be a simple task in most cases if we were set up to weld aluminum.      As you probably already know welding aluminum requires special equipment. Although aluminum can be welded with oxy-acetylene equipment, it is difficult because of the following: Compared to other metals aluminum has a very low melting point, about 1220 degrees F. Due to its light color there is no indication when the melting point is reached, when the metal begins to melt it collapses suddenly. When hot, aluminum is very weak and flimsy. For these reasons aluminum is normally welded with Gas Tungsten Arc (Tig) or Gas Metal Arc (Mig) welding equipment. These are some expensive pieces of equipment and I don't have any of them in my shop.      A while back I came across a system that will weld aluminum and is not expensive at all. You use regular propane gas in a torch like you can buy at Wal-Mart for about $10. The system is called Dura Fix Aluminum Welding Rods and you can get about 32 rods for about $30. These rods work better than the older rods that I have tried a few years back. They are larger in diameter, 1/8 inch, and they can really fill open holes with ease. If you had a hole in your muffler that you wanted to fill, for example you moved a down pipe over to another location and the hole is ¾ inch in diameter, it can be done with ease. Simply heat the surrounding area around the hole, you do not heat the rod just the work area. When the temperature reaches 732 degrees F the rod will begin to melt and flow over the hole. As the rod melts move it around the hole in a circular motion and you will be amazed how it fills the hole. I don't know how big of a hole you can fill, at least 1 inch I would think. You use the same procedure for welding butt joints, do not heat the rod or it will break off in small pieces.      What is really amazing is the fact that the weld is much harder and stronger that the original aluminum. Just try to drill it and you will see how hard it is. Try to pull it off and you will pull a plug of base aluminum with it. It is ideal for our hobby and I plan to use it a lot. The key to a good weld is cleaning the base aluminum before the weld is attempted. A nice brass brush comes with the kit and is really all you need to clean most jobs. If the aluminum has a lot of oil on it I would recommend cleaning it with alcohol first, even though the 732 degrees will burn off most oils. If anyone is interested in these rods give me a call for the phone number.