Materials; Sheet-Metal Allowance: Determining How Much Sheet Metal Is Needed to Make Curved Parts. When engineers need to make curved or bent pieces of sheet metal, they use company-written tables ...

BENDING SHEET METAL Straight-line bends and folds in sheet metal are ordinarily made on the cornice brake and bar folder; however, a considerable amount of bending is also completed by hand-forming methods. Hand forming may be accomplished by using stakes, blocks of wood, angle iron, a vise, or the edge of a bench. Understanding the Bend Allowance and consequently, the Bend Deduction of a part is a crucial first step to understanding how sheet metal parts are fabricated. When the sheet metal is put through the process of bending the metal around the bend is deformed and stretched. As this happens you gain a small amount of total length in your part.