By experimentation with actual bends in metals, aircraft engineers have found that accurate bending results could be obtained by using the following formula for any degree of bend from 1 to 180:

Refer to the NA 01-1A-1 for the appropriate bend allowance tables.

Once a project has been laid out on the metal, the next step is to cut it to shape. The type of cutting equipment to be used depends primarily upon the type and thickness of the material. Another consideration is the size and number of pieces to be cut. A few relatively thin pieces of comparatively soft metal may be cut faster with hand-trimming methods. But for harder metals, faster output, and more professional results, machines designed for metal-cutting purposes are used.

Machines used to cut sheet metal may be divided into two groupsmanually operated and power operated. Each cutting machine has a definite cutting capacity that should never be exceeded. A few of the more common types that may be available to you have been described in the previous sections.