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90 Degree Bends

When developing flat length for 90 degree  bends always make sure the dimensions are outside  to outside. Using the example to the right let us  say the material thickness is .050 and the bend  radius is .032. Our bend allowance would be:    (.0078 x .050 + .01743 x .032) x 90 = .085  Now we can calculate the bend deduction:           2 x (.050 + .032) = .164            .164 - .085 = .079 B.D. Look at the two pictures closely and notice  the different way each is dimensioned. They are  both identical parts. The first picture is shown  dimensioned like a typical blueprint. The second  is the dimensions we need for our flat pattern  development. We got the bottom dimensions from  the information on the first drawing.  Note that the .370 dimension is located from  outside of a bend to the inside of a bend. We  will have to add a material thickness to the .370  dim. making it .420. The 1.050 dim. on the bottom  picture came from subtracting .740 from 1.740  which would give us a distance of 1.000 from  outside to inside. Now we have to add a material  thickness to the 1.000 dim. making it 1.050 which  now gives us all of our outside dimensions. We  can do our development next.  Below is an easy way of keeping track of our  bends and bend deductions. You can count the  B.D.'s and see that we are figuring for 3 bends.  .740 -.079 B.D. .661 +.420 1.081 -.079 B.D. 1.002 +1.050 2.052 -.079 B.D. 1.973 +1.000 2.973 = Flat stretch out