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Two ways"

Jim Markle's bending Pietenpol horn bends

and

My Method

Like many builders, I really had no clue how I was going to make the formed control horns. Fortunately over the years I had gleaned enough information from other builders to be ready to give them a try.

My first attempt was to simply make two bends. In the following pictures you can see the bends making facets not a smooth curve.  

Though it wasn't exactly like the plans I thought it turned out ok  

However, someone said they though I could do better.  Well, who could turn down such a challenge.

My next attempts match the plans much better and wasn't that difficult.  Like every thing on this plane it just takes time. Here is how I do it.

These are the tools I used they consist of two bending blocks, a 1/2-inch round bar, pen, bronze bar and hammer (not pictured) to form the metal.  I use the bronze bar to form the metal because wood splinters to easy and bronze is softer then steel so it doesn't leave a mark when you pound on it.

After cutting out the horn I first drill the holes on the ends and make the cuts for the flanges that need to bend out.  As you can see I didn't do so well at following my line on one corner.  I fixed it by drilling the hole a little larger.

   I then mark the location of the bends. I added a little bit of extra material in the leading edge to help get the curved shape.  Maybe 1/16^th of an inch.

    I then bend the two flanges out.

Next I  bend the leading edge.  It needs to be bent around a large radius so I made  a 1/4-inch radius on my bending block (ground on a grinder then smoothed with sandpaper).

Line up the bend line on the horn with the start of the radius on the block. In the picture you can see that I am above the line on the one end to help taper at the end. I use a brass bar to form my bends because it will last longer than hardwood and is softer then the steel so it will not leave marks.   Try not to hit it with just the hammer

You can see in this picture I have formed both leading edge bends. Do this on another piece making sure to make a left and right side.

To hold the two pieces together you can pit some bolts in the end holes.  Check to see ho the leading edges line up and that they are symetrical.

you will notice the trailing edge and  end do not line up yet.

Time to form the end radius

I ground a 1/4-inch radius on the end of a 1/2-inch steel rod.  Mounted this in my vice and gently tapped on the end of the control horn piece.

  You will notice that the trailing edges will now line up better.

On the plans you will see there is a brace that extends off the back of the horn. The only way I could figure out how to get the metal strip into the horn was to form a jog. I formed this jog over a piece of steel 1/2 the thickness of the brace.

Time to weld

I used a lot of clamps to hold the two halves together. Because the metal is so thin I used a 1/16-inch welding rod sparingly. On the trailing edge I simply fusion welded, no added filler rod, because the two halves are almost parallel to each other.