In our example below a part with flange lengths of 2” and 3” with an inside radius of. The flange lengths are always measured to the apex of the bend. The Bend Deduction is defined as the material you will have to remove from the total length of your flanges in order to arrive at the flat pattern. Likewise when you are trying to develop a flat pattern you will have to make a deduction from your desired part size to get the correct flat size. As this happens you gain a small amount of total length in your part.
When the sheet metal is put through the process of bending the metal around the bend is deformed and stretched. Understanding the Bend Deduction and consequently the Bend Allowance of a part is a crucial first step to understanding how sheet metal parts are fabricated.
