BEND ALLOWANCE-

The design approach and the progression would be somewhat different if the example shape were to be made from a lighter gauge material, say .0359 (20 ga.) cold rolled steel, as in Fig 5.1:

Fig. 5.1

The commercial tolerance for the strip material would be .002 for the thickness, and would be .005 for the strip width. Using the bend allowance formula as before:

The bend allowance for the .125 radii will be:

The bend allowance for the .250 radii will be:

DEVELOPED WIDTH-

The lengths of the straight elements are defined in Fig. 5.2:

Fig. 5.2

Developed Width=2.(637+.175+1.200+.339)+.810=5.512

Though the product shape has the same nominal width and height as the first example except for the material thickness, the resulting developed width of the strip material is .126 wider. The commercial tolerance for the thickness of 20 ga. cold rolled strip is .002, so variation in the material thickness being processed will result in much smaller change in the end product than the previous example. When the upper roll is adjusted downward to the .034 material gap, the resulting product shape would have the dimensional changes shown in Fig. 5.3:

Fig. 5.3

At the minimum material thickness, the bend allowance for the .125 radii will be:

The bend allowance at the nominal material thickness of .036 was .1754, so the change at the minimum material thickness of .034 is .1754 ?.17475=.00065.

Similarly, the bend allowance for the .250 radii at minimum material thickness will be:

The...