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allowance for a particular application. By experimentation with actual bends in metals, aircraft engineers have found that accurate bending results could be obtained by using the following formula for any degree of bend from 1° to 180°. 

Bend allowance = (0.01743R + 0.0078T)N where: 

R = the desired bend radius T = the thickness of the metal N = number of degrees of bend 

To use this formula for a 90° bend having a radius of .16- inch for material 0.040-inch thick, substitute in the formula as follows: 

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## Use of Bend Allowance Chart for a 90° Bend 

In Figure 4-128,  the radius of bend is shown on the top line, and the metal thickness is shown on the left hand column. The upper number in each cell is the bend allowance for a 90° bend. The lower number in the cell is the bend allowance per 1° of bend. To determine the bend allowance for a 90° bend, simply use the top number in the chart. 

Example: The material thickness of the U-channel is 0.040- inch and the bend radius is 0.16-inch. 

Reading across the top of the bend allowance chart, find the column for a radius of bend of .156-inch. Now, find the block in this column that is opposite the material thickness (gauge) of 0.040 in the column at the left. The upper number in the cell is (0.273), the correct bend allowance in inches for a 90° bends. 

Several bend allowance calculation programs are available online. Just enter the material thickness, radius, and degree of bend and the computer program calculates the bend allowance. 

## Use of Chart for Other Than a 90° Bend 

If the bend is to be other than 90°, use the lower number in the block (the bend allowance for 1°) and compute the bend allowance. 

## Example: 

The L-bracket shown in Figure 4-129  is made from 2024-T3 aluminum alloy and the bend is 60° from flat. Note that the bend angle in the figure indicates 120°, but that is the number of degrees between the two flanges and not the bend angle from flat. To find the correct bend angle, use the following formula: 

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The actual bend is 60°. To find the correct bend radius for a 60° bend of material 0.040-inches thick, use the following procedure. 

1. Go to the left side of the table and find 0.040-inch. 

2. Go to the right and locate the bend radius of 0.16-inch (0.156-inch). 

3. Note the bottom number in the block (0.003034). 

4. Multiply this number by the bend angle: 0.003034 × 60 = 0.18204 

