Making a reverse shape in sheet metal
I've been working on a method for making mild reverse shapes that is a little easier than stretching the edge of a panel. A reverse is where instead of a crown or bulge in the body, you have a concave area. An example of this would be the cowl area on some early cars....or where a fender flare blends in with the body on a later car. In this case, you would have a normal outward curve up and down and a reverse curve front to back. Usually you stretch the edge of the panel that you want the reverse shape in to make it grow and create a valley just inboard of the edge. You stretch a lot on the edge and less as you blend the reverse into the panel. This can be very tricky, and your panel can get away from you.
Using a crowned shrinking disc, I made about 12 passes in a sample piece. The sample was rolled over my leg first to make a curve similar to what I would do for a fender flare where it meets the door gap. Instead of stretching the edge, I shrunk the valley. The panel is a little easier to control this way.
I've attached three pictures. The first one is an example of a typical reverse. The reverse is where my hand is pressing on the flow strip. The fender flare was stretched making a valley (reverse) in the transition area between the flare and body.
The second and third pictures are of the test panel I shrunk a reverse in. I will be playing with this method some more to see how far I can take it. I think a combination of shrinking the valley and a mild stretching of the edge will come in handy at some point.