Bend allowance comes from the fact that when sheet metal is bent, the inside surface of the bend is compressed and the outer surface of the bend is STRETCHED (ELONGATED).

So, when we want a 90 degree bend in which one panel side has a length of A, and the other panel side has a length of B, the total length of the FLAT piece will NOT be A+B, but rather equals A+B plus a bend allowance or A+B MINUS a bend deduction(depending on how we measure A and B).

So bend allowance is a term which describes how much material is needed between two panels to accommodate a given bend. Determining bend allowance is commonly referred to as “bend DEVELOPMENT” or simply “development”.

Bend allowance comes from the fact that when sheet metal is bent, the inside surface of the bend is compressed and the outer surface of the bend is stretched (elongated).

So, when we want a 90 degree bend in which one panel side has a length of A, and the other panel side has a length of B, the total length of the flat piece will NOT be A+B, but rather equals A+B plus a bend allowance or A+B minus a bend deduction(depending on how we measure A and B).

So bend allowance is a term which describes how much material is needed between two panels to accommodate a given bend. Determining bend allowance is commonly referred to as “bend development” or simply “development”.