Sheet Metal Bending Brake for Dorsal and Ventral Fins

I made a little progress on my Bede BD-4C airplane this week, though it is not photogenic enough to show here. I made two small steel plates which will attach the tail skid to the fuselage. They are drilled and clecoed in place, waiting for the welder to bend the ½ inch 4130 steel tube into the proper shape. I’ve tried bending this stuff cold and there is no way I can do it so every time I need some of the 4130 steel tube bent, it goes to the welder where he fills it with sand and heats it with a torch.

I then turned my attention to the dorsal fin and the ventral fin. I get to fabricate these out of sheets of .025 and .020 inch aluminum, respectively. The trick is that the dorsal fin needs a .25 inch bend radius and the ventral fin needs a .5 inch bend radius… and they each need to be bent to about 160 degrees, which is way more than the 100 degrees or so that my bending brake will do.

Using a few scraps of 2×4 and some spare hinges that I had sitting around, I created a crude brake that will bend all the way to 180 degrees. I put it together with a .25 inch gap between the jaws so it will work for the dorsal fin. To bend the dorsal fin, I will take the brake apart and reassemble it with .5 inches between the jaws. Here are the photos (click on them to see larger versions).

To make the actual bend in a test piece of aluminum, I taped a piece of .25 inch dowel along the bend line. Then I used my real bending brake to start things off. That worked well because it actually clamps the metal and holds it tight. Once I had the metal bent to about 90 degrees, I held it in place in my handmade brake while my son, Kevin, operated the jaws. The result looks pretty good, IMHO.

Much as I wanted to keep going and make the actual dorsal fin, it was way too hot in the garage so I quit for the day. Sometimes, it’s hard to tell whether I live in St. Louis or in a sauna. :-/