Q Ron, I am having trouble with turning a flange on the curved edge of a panel. I've been using a set of tipping dies in a bead roller, and that works well enough on gentle curve, but tighter curves prove difficult to shrink or stretch (after the flange is turned to nearly 90 degrees) with hand-operated shrinkers or stretchers, since the curved flange will not fit between the jaws of the machine. How do you go about this process?
Andy Perazzo - Via the Internet
A There are several variables here, such as the type of metal, the metal thickness, the width of the flange, and the radius of the curved edge of the panel. Let's take a look at a real world example, where I need to form a 5/16-inch flange on the edge of a 19-gauge steel door skin that has a straight front, back, and bottom, but has a 2-inch radius curve on the lower rear corner.
In this case, I would start tipping the flange with either a bead roller, or with piece of scrap metal with a notch cut in it the depth I want the flange to be, or even with a pair of pliers or Vise-Grips. As you know, the straight sections aren't very difficult, but the metal will start to wrinkle on a radiused corner. After tipping the edge to about 10 or 20 degrees, I'd start working with a hammer and dolly. I'd back the flange up with a heel dolly, holding it so the flat face of the dolly was touching the door skin, but the curved edge of the dolly was positioned right at the base of the tipped flange. Now, I'd slowly start hammering on the flange, slowly increasing its angle, working back and forth around the radiused edge. The metal in the flange will tend to form more ruffles, but by carefully hammering off-dolly, they can probably be worked out completely.
There are limitations on what you can do with this process-for example, it won't work with a flange 1-inch wide on a 2-inch radius corner, or with a 5/16-inch flange on a corner with only a 1/4-inch radius. In these situations you will probably need to use heat to help shrink the ruffles out, or you may need to trim the flange width down smaller in these areas to make it possible. If you look at the door skins of production trucks, the width of the hemmed edge is often decreased in the difficult areas for this very reason.
Let me know if you need more pointers on this process-I've just hit the high points, assuming that you'll probably figure out the rest with a little practice!
A Call To Readers For Clever Tools And Fixtures:Classic truck builders often design and make some very imaginative tools and fixture to help build their projects. If you have built or modified a tool or fixture that you think might be helpful to other builders, send a photo and description to Ron Covell (contact information to the left). This could be for bodywork, chassis work, engine work, or any other aspect of truck building. I'll be eager to see your ideas, and we may run some of the best ideas in future "Professor Hammer" columns, so our readers can benefit from your creativity!