Q. I'm trying to roll an indentation into the center of a piece of 18-gauge cold-rolled steel. Well, after running it through the rollers, the panel is warped pretty much like a potato chip, and I'm having a hard time understanding what's going on. If I press it flat, the sides roll into waves, which I think indicates it needs shrinking, but where? One person told me that I need to shrink the corners, but another says I need to shrink the sides and stretch the corners. I've always enjoyed your articles and watching your DVDs, so if you have something that addresses this subject, please let me know.

How do you suggest getting this metal flat, and why did it buckle in the first place? Does it need stretching, shrinking, or both? Would pre-stretching the metal with a planishing hammer have helped? Is there a different shape die that would work better? My bead roller is an inexpensive import, but I beefed up the frame, softened the edges of the step dies, and offset them to make a wider detail.

Mat McClary
Via the Internet

A. Beading machines are notorious for putting stresses in metal that result in twisting or warping. This seldom happens if the detail is a straight line that goes across the panel all the way from one edge to another. Unfortunately, if the detail (whether a bead or a step) stops short of the edge, or worse, changes direction abruptly, distortion is very likely to happen. The larger the feature, the greater the depth, and the thicker the metal, the more distortion you're likely to get.

The basic problem is that the dies of the machine are attempting to stretch the metal, and the metal has a powerful resistance to stretching. This resistance is so great it pulls on the metal next to where the dies contact the metal. It is this imbalance of forces that causes the tension in the panel.

The detail in your picture is a step, or "joggle," but I'm going to talk about beads here, because they are a more extreme example of the same problem. Sometimes if you pre-stretch the metal where a bead will go, that can help reduce the warping and twisting especially where the beads are straight, and stop short of the edge(s) of the panel. My "Planishing Hammer Basics" DVD has a good example of how this is done.

Unfortunately, this doesn't work nearly as well when the bead changes directions, and a 90-degree change, like your part has four of, is especially difficult to pre-stretch just the right amount. In theory, the metal could be pre-stretched exactly the right amount, so that when the bead is formed, the panel lays flat, but all of the stretching has to happen exactly where the bead will go, and in your example, that appears to be a zone only about ¼-inch wide. With hand-operated tools, it's just not feasible to stretch the metal uniformly in such a tiny area.

I think the best way to fix your panel is to cut out the corners, where most of the stress is, allowing the metal to relax. I've drawn some red lines on one corner that show where the cut would be made. You should definitely clamp the metal flat against a heavy plate as the new filler piece is tacked and welded. If you clamp it to aluminum or copper, the weld won't stick to it, but with a steel backing, you could have a big problem! Clamping the metal will hold everything flat, diminishing the distortion in the panel, and the clamping plate will act as a heat-sink, so the weld heat will not propagate as deeply into the panel, which will also be beneficial.

I don't think changing or re-making your dies would help at all. Even with new dies, you would have similar problems if they displace the metal the same amount as the old ones.

You can email your questions to Professor Hammer at covell@cruzio.com, or mail to Professor Hammer, c/o CLASSIC TRUCKS Magazine, 1733 Alton Pkwy., Irvine, CA 92606. You'll receive a personal reply! We'll print your name and city unless you request otherwise. Ron Covell has made many DVDs on metalworking processes, and he offers an ongoing series of workshops across the nation covering all aspects of metalworking. Check them out online at www.covell.biz, or call for a current schedule of workshops and their free catalog of DVDs. Phone 800-747-4631, or 831-768-0705. You can send a request by mail to: Covell Creative Metalworking, 106 Airport Blvd. #105, Freedom, CA 95019. You'll also enjoy Ron's YouTube channel: youtube.com/user/covellron.