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Example 1 

Bend radius = 0.22-inch 

Material thickness = 0.063-inch 

Bend angle = 90º 

ML 1 = 2.00/ML 2 = 2.00 

Use a straightedge to connect the bend radius (0.22-inch) at the top of the graph with the material thickness at the bottom (0.063-inch). Locate the 90° angle on the right hand scale and follow this line horizontally until it meets the straightedge. Follow the curved line to the left and find 0.17 at the left side. The X factor in the drawing is 0.17-inch. [Figure 4-133] 

Total developed width = (2 + 2) – .17 = 3.83-inches 

Example 2 

Bend radius = 0.25-inch 

Material thickness = 0.050-inch 

Bend angle = 45º 

ML 1 = 2.00/ML 2 = 2.00 

Figure 4-134  illustrates a 135° angle, but this is the angle between the two legs. The actual bend from flat position is 45° (180 – 135 = 45). Use a straightedge to connect the bend radius (0.25-inch) at the top of the graph with the material thickness at the bottom (.050-inch). Locate the 45° angle on the right hand scale and follow this line horizontally until it meets the straight edge. Follow the curved line to the left and find 0.035 at the left side. The X factor in the drawing is 0.035 inch. 

Total developed width = (2 + 2) – .035 = 3.965-inch 

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Total developed width = (Mold line 1 + Mold line 2) – X factor 

Total developed width = (Mold line 1 + Mold line 2) – X factor 

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## Using a Sheet Metal Brake to Fold Metal 

The brake set up for box and pan brakes and cornice brakes is identical. [Figure 4-135]  A proper set up of the sheet metal brake is necessary because accurate bending of sheet metal depends on the thickness and temper of the material to be formed and the required radius of the part. Any time a different thickness of sheet metal needs to be formed or when a different radius is required to form the part, the operator needs to adjust the sheet metal brake before the brake is used to form the part. For this example, an L-channel made from 2024 –T3 aluminum alloy that is 0.032-inch thick will be bent. 

## Step 1: Adjustment of Bend Radius 

The bend radius necessary to bend a part can be found in the part drawings, but if it is not mentioned in the drawing, consult the SRM for a minimum bend radius chart. This chart lists the smallest radius allowable for each thickness and temper of metal that is normally used. To bend tighter than this radius would jeopardize the integrity of the part. Stresses left in the area of the bend may cause it to fail while in service, even if it does not crack while bending it. 

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