 In a typical press break bending operation, a piece of metal is placed between the upper and lower dies and formed by means of the force and pressure exerted by lowering the ram. On some press breaks, the ram and upper dies remain stationary, while the bed holding the lower dies provides the force that bends the part. Three contact points are involved in a bend, the tip of the punch and two points on the female die. The material is bent to the desired angle as the punch enters the die. The larger the die opening, the smaller the force required to form a given angle. The principal terms used to describe bending on press breaks are bend allowance, bend angle, bend radius, and spring back. Bend allowance is the pre-bent length of material that must be included in a blank to allow for any deformation that occurs due to the bending operation. The bend angle is usually the included angle of the bent work piece. It can also refer to the supplementary angle formed by the two bent tangent lines. The bend radius is a tangent line where the flat, straight section of the part stops and the radius of the bend begins. Spring back is the tendency of the material to return to its original form. Spring back typically ranges from two to four degrees.