Today’s modern bending techniques allow almost any tube or pipe to be formed to almost any desired bending radius. However, designing bends to some radii will cost more than others. Some radii require custom built dies or expensive machinery and labor to achieve the bend. Many bending applications have some flexibility in the radius they can use.
When possible, use a common bending radius and adjust the tangents on each end of the bend to yield the overall required dimensions. Small, tight radius bends should use the largest radius possible. Typically, the bigger the radius, the easier the bend is to make without serious deformation, such as ovality or wrinkles in the material.
If the radius can be big enough, design it in increments of feet, i.e., 12-inch radius, 24-inch radius, 36-inch radius. If your project does not allow such a big radius, design the radius as a multiple of the nominal outside diameter of your material, such as 3R, 5R, or 10R, where R stands for the radius factor.
In other words, if you are designing bends in 2-inch pipe (2.375-inch OD), a 3R bend would be 2-inch (pipe) x 3 (radius factor) = 6-inch radius; a 5R would produce a 10-inch radius; and a 10R would produce a 20-inch radius.
Designing bend radii around the common dies available through most bending operations will also reduce the cost of your bending project.