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 🤓 This causes a slight increase in the length of your piece 🙌 If you want to create a flat-pattern, then you must subtract your desired part size from it. In order to create a flat-pattern, you need to add the Bend Allowance to the length of your part. The length of the leg is the portion of the flange that lies outside the bend radius. In our example below a part with flange lengths of 2” and 3” with an inside radius of .250” at 90° will have leg lengths of 1.625” and 2.625” respectively. When we calculate the Bend Allowance we find that it equals .457”. In order to develop the flat pattern we add .457” to 1.625” and 2.625” to arrive at 4.707”. The Bend Allowance as well as Bend Deduction are very closely related, as you will see. 
Metals tend to be extremely stiff. A material that doesn’t bend will most likely break at the point it had is bent. At 411 GPa, tungsten ranks as the hardest of the alloys. Even when tungsten appears thin, it is extremely difficult to bend. Therefore, tungsten will break like glass. At 304 GPa, beryllium-copper is the second stiffest metal. With 279 GPa, chromium (a metal found in diamonds or other gemstones) is third. Both wrought iron as well as cobalt are at 211 GPa. At 210GPA, there are many common metals used in sheet metal such as nickel, steel, stainless, cobalt and steel. Most metals can be considered extremely stiff. However, as you will see, there are some metals that are more stiff than others. This page was last modified 43 days back by Satyra Kang from Jubayl in Saudi Arabia. 
Two basic methods can be used to create a flat blank. The information you have will determine which method to choose. You can use the second method. Need to know The leg dimensions. Any flat area in a part is called a leg. It can be between bend radii, or between edge radius and an edge. The second method requires you to measure the distance from the edge, (formed or cut), to the apex, or intersection between the planes running parallel to each other. Jessica Walker, Beijing, China (September 3, 2021 modification) 
Let’s start with a simple L bracket. The picture shows that the legs of the bracket are 2” and 3”. The material thickness is 0.125”, the inside radius is 0.250”, and the angle of bend is 90 degrees. Flat length equals the combined flat area of both flanges, plus the length through the bend region. Do you compute it on the outside of the material? Neither! The K-factor is here. K-factor refers to the percent of material thickness that is not subjected to stretching or compression, such as the neutral axis. A K-factor 0.42 will be used for this L bracket. Aleshia Boykin, December 24, 2021. 
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