Just bought an inexpensive baking pan hoping it would fit an old toaster oven. Only $1, and it seemed decently made so took the chance.
I found it would fit by bending the flanges down along the short edges. To my surprise, the pan, which had been quite flat on the bottom, developed a sharp bistable twist. The bending was done freehand, using fingers alone.
Would holding the pan flat during the bend have avoided the twist, or is the twisting intrinsic to deforming a drawn shape of this sort? Can a twist be "tuned out" of a drawn shape? More pans are available if it's necessary to start over. It's very easy to make the twist worse, but making it better requires visualization skills I lack.
The pan is about 11 by 7 by 1 inch deep, the flanges I bent down were along the 7 inch edges. The twist that resulted is close to half an inch.
Thanks for reading, and any ideas.
It's really hard to tell without handling the pan, but perhaps the edges of the bottom have been stretched larger than the center. Making many narrow bends sequentially can do that, since the metal stretches to accommodate being bowed out. If the center was larger the edges would be stable and the bottom would bulge and be in/out bistable. Hammering around the center against a solid steel block might stretch it enough to remove the twist, though judging where and how much to hit is tricky, an acquired skill. An auto-body planishing hammer with a smooth face is neater than a ball pein.
Vise-Grip or other flat jaw sheet metal pliers are very handy, I used them to fine-tune the shape of the air cleaner latch I made. When you need a bend longer than your tooling allows, change the angle gradually and uniformly up and down the length to avoid stretching. Clamping the metal between two wood blocks below the bend line and pounding on a third block pressed down against the bend line is simple, neat and effective.
I added 10 years to the life of my car by making and welding in fender-shaped metal rust patches, some of which are barely visible. The lowest body shop quote to fix one quarter-sized hole was $800 and the dealer's body shop wanted $3000, an incentive for me to learn to make the compound curved wheel well lip detail. The first patch paid for the whole (used) MIG setup plus night school cost.