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Actual Bend Tests
This is the most accurate way of determining a bend deduction. For example bend allowance formulas are not very accurate if using them on thicker materials with extremely small bend radii. Remember you have to stay in the air bending range for these formulas. Because bend allowance formulas are only theoretical they may be slightly different from actual results. With today's tolerances slightly may be too much. When in doubt or if tolerances are very critical (i.e. ±.005) it is best to pre- bend a piece of material with the exact brake tooling you expect to use to find out what the bend deduction will be. For Example: Take a piece of material that is exactly 2 inches wide. Place your tooling in the brake and bend some samples until you get the exact angle and radius you need. Now bend your 2 inch piece and then measure the two flanges, outside to outside, and add them together then subtract your 2 inches. This is your Bend Deduction. To be on the safe side if bending thick materials with very small or very large radii, exotic materials, very soft (malleable or ductile), very hard (brittle) materials or extremely close tolerances then you should probably use the actual bend/test method . After you have done this for a particular material and radius keep a log of these bend deduction values for your shop so you don't have to go through this again. This value will pretty much remain constant. The log can look something like this: COLD ROLL STEEL 90 Degree Bends