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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
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