Why is my sheet metal flat pattern length incorrect? This is a common question I hear from SOLIDWORKS users. The answer, however, is surprisingly simple. Almost certainly the calculation method you are using differs from the calculation method used by SOLIDWORKS Although the answer is simple, that probably doesn't help solve the problem. So let me elaborate. SolidWorks uses one of three methods to calculate develop length, bend allowance, bend deduction or k factor when calculating to developed length manually typically bend allowance or bend deduction are used. However, the default method for SolidWorks is k factor. This is often the root cause of any incorrect developments. Also, the default K factor value is 0.5, which is often unsuitable. A bend allowance calculation uses the sum of the straight lens and B excluding the bend region. Then as the bend allowance values specified by the user in a similar way to bend allowance, a bend deduction calculation uses the sum of the straight lens A and B this time including the bend region and subtracts the bend deduction value in K factor calculations. Use the sum of the straight lengths and B excluding the bend region. Then and on the length. The Arc length is derived from a neutral access position by a specified value. This is a unitless value between zero and one. zero positions The arc on the internal surface of the bend and one positions the arc on the external surface of The bend k factor is a user friendly method of calculating the develop length. This is due to the fact a single use defined value can cover all situations. However, in situations where accuracy is paramount, bend, allowance or deduction tables are usually employed.