TECHNICAL FEATURE

COMPOUND FORMING

ALUMINUM

You Don't Have To Be Houdini BYBUDDDAVISSON

A

truly amazing thing happens when someone takes the time to show you the basic concepts behind some of the more baffling secrets of aviation. Suddenly the entire concept makes sense and it no longer looks like something only attainable by supermen.

That is exactly the way it is in forming aluminum into compound curves. From the outside it looks as if only Houdini could do it, but stand backstage and watch Houdini prepare his tricks and suddenly it's no longer magic. It is the simple application of understandable basic concepts. Suddenly you find yourself saying, "Hey, I could do that." That is what happens when you spend a few hours following Jim Younkin (the Houdini of aluminum) around at his Historic Aviation in Springdale, Arkansas. Spend just a little time listening to him explain as he's hammering on

All of these pieces can be formed using the same techniques and tools shown. The black lines indicate where stretching would be so great it was easier to weld in a separate, pre-formed piece or join two pieces together to form the final part.

This is the entire tool kit needed to make the part. The shot bag could be square, but the cut-out is almost mandatory for many curves. Your local shoe shop can make this for you and the shot is available at your local gun store. 88 NOVEMBER 1995

The universal dolly made by Younkin is actually a bunch of steel pipe fittings welded together and ground smooth to give as many different shapes as possible. It isn't necessary for this part but made it much easier. A 2-1/2" elbow welded to a T fitting would give everything needed for this part.

a piece of aluminum, transforming it

into a seemingly impossible shape, and

suddenly you wonder why you've been wasting so much time using fiberglass. Of course, in watching Jim, you are

taking advantage of a 20 year learning

curve. He's paid his dues and we're getting in for free. If in reading this article you learn nothing else, it should be that a vast portion of the aluminum fairings needed for an airplane can be made by the average craftsman and in a fraction of the time it takes to do the same part in fiberglass. And, on top of that, the parts are much, much lighter. Besides, it's great to be able to say, "No, it's all aluminum." It is going to be impossible to cover all the different aspects of compound forming aluminum in anything shorter than a complete book or a two hour video, so in the interest of brevity, we're going to speak specifically about free forming aluminum using nothing but basic hand tools. Also, there are a lot of different ways to form the same part, like beating it down into a form or rolling it, and we'll get into those in a later article. However, this one is focusing on the easiest, quickest way of forming aluminum and the way which is most useful to the most people.

Like we said, it doesn't take sophisticated tooling. This is what is used for the initial

stretching operation for the inside of the strut fairing.

FIRST THE TOOLS Buy at least three different sizes of shot-filled plastic mallets, a smallish ball peen hammer, and one or two of those plastic tipped mini-mallets. You can grind those into specific shapes needed. Then you'll need a shot bag. These can be bought from mail order automotive houses or they can easily be made at your local shoe shop out of mediumheavy leather. Just buy a bag of number 7 shotgun pellets at your local gun store and have a leather bag stitched up for it. Then you'll need a box full of different sizes of steel pipe, pipe fittings, bent heavy tubing and just about anything made of steel you can use to hammer aluminum around. You could even sand a shape out of maple, if necessary. See the photos for the initial bend form Jim used for the inside of the strut fairing he was making. You'll also need at least three different pairs of aviation snips, for straight, right and left hand cuts. :. ••>.:. ;