Abstract
Besides the torsion stress which can be calculated from twisting moment and cross section, other, secondary, stresses appear in volute springs; these are caused chiefly by the variation of twist from section to section or by bending of the spring. They may reach high values in the small-diameter coils. An approximation theory is given for the calculation of secondary stresses; strain-gage measurements and distortions of springs are shown. It is proposed to reduce the stresses on the smallest coils by three means, all of which would facilitate manufacture: (a) By increasing the inner diameter of the spring; (b) by supporting the ends more firmly with full-thickness stub tails; (c) by winding the straight blade on a slightly conical mandrel to produce a variable helix angle and more desirable stress distribution.
