Open End Bend (Less Than 90°) Closed End Bend (More Than 90°) Hand Forming Straight Line Bends 4-74 Figure 4-147.  Open bend.  Figure 4-148.  Closed bend. 3.  Calculate bend allowance for 135°. Look up bend  allowance for 1° of bend in the bend allowance chart  and multiply this by 135.  2.  Calculate SB. 1.  Look up K-factor in K chart. K-factor for 135° is  2.4142-inch. 5.  Calculate TDW 4.  Calculate flats.  3.  Calculate bend allowance for 45°. Look up bend  allowance for 1° of bend in the bend allowance chart  and multiply this by 45. 2.  Calculate setback. 1.  Look up K-factor in K chart. K-factor for 45° is  0.41421-inch. 4.  Calculate flats.  5.  Calculate TDW. After a blank has been laid out and cut to size, clamp it along  the bend line between two wooden forming blocks held in  The cornice brake and bar folder are ordinarily used to make  straight bends. Whenever such machines are not available,  comparatively short sections can be bent by hand with the  aid of wooden or metal bending blocks. For example, if a formed or extruded angle is to be curved,  either stretch one leg or shrink the other, whichever makes  the part fit. In bumping, the material is stretched in the bulge  to make it balloon, and in joggling, the material is stretched  between the joggles. Material in the edge of lightning holes  is often stretched to form a beveled reinforcing ridge around  them. The following paragraphs discuss some of these  techniques. All hand forming revolves around the processes of stretching  and shrinking metal. As discussed earlier, stretching means to  lengthen or increase a particular area of metal while shrinking  means to reduce an area. Several methods of stretching and  shrinking may be used, depending on the size, shape, and  contour of the part being formed. It is obvious from both examples that a closed bend has a  smaller TDW than an open-end bend and the material length  needs to be adjusted accordingly. Observe that the brake reference line is still located one radius  from the bend tangent line.  Figure 4-147  shows an example for a 45° bend. Flat = Mold line dimension – SB Flat 1 = 0.77-inch – 0.57-inch = 0.20-inch  Flat 2 = 1.52-inch – 0.57-inch = 0.95-inch SB = K(R + T) SB = 0.41421-inch(0.1875-inch + 0.050-inch) =  0.098-inch 0.003675-inch × 45 = 0.165-inch Flat = Mold line dimension – SB Flat 1 = .77-inch – 0.098-inch = 0.672-inch Flat 2 = 1.52-inch – 0.098-inch = 1.422-inch TDW = Flats + Bend allowance TDW = 0.672-inch + 1.422-inch + 0.165-inch = 2.259-inch. TDW = Flats + Bend allowance TDW = 0.20-inch + 0.95-inch + 0.496-inch = 1.65- inch SB = K(R + T) SB = 2.4142-inch(0.1875-inch + 0.050-inch) = 0.57- inch 0.003675-inch ×  135 = 0.496-inch Figure 4-148  shows an example of a 135° bend. 135° 1.52 R .19 0.77 1.52 R .19 45° 135° 0.77 0.05