Allowances for Bending Sheet Metal

(From Oberg Jones Machinery's Handbook 27 edition: 2004, pages 1335 to 1338)

In bending steel, brass, bronze, or other metals, the problem is to find the length of straight stock required for each bend; these lengths are added to the lengths of the straight sections to obtain the total length of the material before bending.

If L = length in inches, of straight stock required before bending; T = thickness in inches;

and R = inside radius of bend in inches:

Angle of Bend Other Than 90 Degrees

For angles other than 90 degrees, find length L, using tables or formulas, and multiply L by angle of bend, in degrees, divided by 90 to find length of stock before bending. In using this rule, note that angle of bend is the angle through which the material has actually been bent; hence, it is not always the angle as given on a drawing. To illustrate, in Fig. 1, the angle on the drawing is 60 degrees, but the angle of bend A is 120 degrees (180 ? 60 = 120); in Fig. 2, the angle of bend A is 60 degrees; in Fig. 3, angle A is 90 ? 30 = 60 degrees. Formulas (1), (2), and (3) are based on extensive experiments of the Westinghouse Electric Co. They apply to parts bent with simple tools or on the bench, where limits of ± 1?64 inch are specified. If a part has two or more bends of the same radius, it is, of course, only necessary to obtain the length required for one of the bends and then multiply by the number of bends, to obtain the total allowance for the bent sections.

Example, Showing Application of Formulas

Find the length before bending of the part illustrated by Fig. 4. Soft steel is to be used.

For bend at left-hand end (180-degree bend):

For bend at right-hand end (60-degree bend):

Total length before bending = 3.5 + 1.338 + 0.707 = 5.545 inches

Note: it's not necessary correcting factors for dimensions in milimiters (mm)

REFERENCE

27th Edition Machinery’s Handbook BY ERIK OBERG, FRANKLIN D. JONES,

HOLBROOK L. HORTON, AND HENRY H. RYFFEL, CHRISTOPHER J. MCCAULEY, EDITOR RICCARDO M. HEALD, ASSOCIATE EDITOR MUHAMMED IQBAL HUSSAIN, ASSOCIATE EDITOR

2004

INDUSTRIAL PRESS INC.

NEW YORK