Patent ID: 8601854

Claim:
A method of determining the starting dimensions of a sheet metal work piece prior to bending into a sheet metal construction using a test work piece formed with an obtuse interior angle, comprising the steps of: providing said test work piece, said test work piece being formed of a same material and having plus or minus 25% of a same thickness, T, as said sheet metal work piece; measuring and recording a length, L and said thickness, T, of said test work piece; bending said test work piece into an angled form, said angled form having an interior angle, Ø; identifying first and second legs of said angled form; measuring and recording a length for said first leg, H 1 , and a length for said second leg, H 2 , each of said lengths including a total distance from an outer edge of one of said legs to an outer surface of an adjacent other leg; measuring and recording a length of a first line, H 3 , descending from said interior angle, Ø, said first line, H 3 , extending from an apex of said angled form to a second line, c, said second line, c, connecting inner edges of said angled form; determining and recording said interior angle, Ø; calculating, a first inside flange length, a=(H 1 −T)/cos(Ø−90); calculating a second inside flange length, b=(H 2 −T)/cos(Ø−90); calculating a first outside flange length, A=(H 1 −T*sin(Ø−90))/cos(Ø−90); calculating a second outside flange length, B=(H 2 −T*sin(Ø−90))/cos(Ø−90); calculating a Bend Deduction, BD=A+B−L; calculating an inside radius, r, comprising the steps of: calculating a length of said line, c=√a 2 +b 2 −2ab*cos Ø, calculating an angle, α, opposite said first inside flange length, a, α=sin −1 ((a*sin Ø)/c); calculating an angle, β, opposite said second inside flange length, b, β=sin −1 ((b*sin Ø)/c); calculating a height of triangle abc, H ! =a*sin β=(a*b/c)*sin Ø; calculating an offset angle, δ=90−(β+Ø/2); calculating a length of a hypotenuse, x=r/sin(Ø/2) in terms of r; calculating inside radius, r, where cos δ=(r+H!−(H 3 −T))/x and r=((H ! −(H 3 −T))*sin(Ø/2))/(cos δ−sin(Ø/2)) calculating a distance of a neutral line from an inside surface of said test work piece, t=((2*tan((90−Ø)/2)*(T+r)−BD)/((π/180)*(180−Ø)))−r; calculating a Bend Deduction for an actual work piece having a finished interior angle, Ø F , BD F =2*tan((90−Ø F )/2)(T+r)−(t+r)(π/180)*(180−Ø F ); calculating a starting length, L F for a work piece having desired outside flange lengths A F and B F , L F =A F +B F −BD F ; and applying said starting length, L F to said sheet metal work piece prior to bending into a sheet metal construction having said obtuse interior angle, Ø F .