content_image/579901.jpg content_image/579902.jpg content_image/579903.jpg content_image/579904.jpg content_image/579906.jpg content_image/579907.jpg content_image/579909.jpg content_image/579910.jpg content_image/579900.jpg content_image/579905.jpg
## Open End Bend (Less Than 90°) 

Figure 4-147  shows an example for a 45° bend. 

1. Look up K-factor in K chart. K-factor for 45° is 0.41421-inch. 

2. Calculate setback. 

<img src='content_image/579901.jpg'>

3. Calculate bend allowance for 45°. Look up bend allowance for 1° of bend in the bend allowance chart and multiply this by 45. 

<img src='content_image/579902.jpg'>

4. Calculate flats. 

<img src='content_image/579903.jpg'>

5. Calculate TDW 

<img src='content_image/579904.jpg'>

Observe that the brake reference line is still located one radius from the bend tangent line. 

## Closed End Bend (More Than 90°) 

Figure 4-148 shows an example of a 135° bend. 

1. Look up K-factor in K chart. K-factor for 135° is 2.4142-inch. 

2. Calculate SB. 

<img src='content_image/579906.jpg'>

3. Calculate bend allowance for 135°. Look up bend allowance for 1° of bend in the bend allowance chart and multiply this by 135. 

<img src='content_image/579907.jpg'>

<img src='content_image/579909.jpg'>

<img src='content_image/579910.jpg'>

4. Calculate flats. 

<img src='content_image/579900.jpg'>

5. Calculate TDW. 

<img src='content_image/579905.jpg'>

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. 

## Hand Forming 

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. 

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. 

## Straight Line Bends 

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. 

After a blank has been laid out and cut to size, clamp it along the bend line between two wooden forming blocks held in 

