Compression Coil Spring Design

P       = axial load, N Do = outer diameter of coil, mm Di = inner diameter of coil, mm d        = diameter of wire, mm           = (Do – Di) / 2 D       = mean diameter of coil, mm           = (Do + Di) / 2 = (Do - d) = (Di + d) p        = pitch of coils, mm δ        = deflection of spring, mm n        = number of active coils C       = spring index = D/d = (4 : 12);               less than 4; it is difficult to manufacture, more than 12; it is likely to buckle. G       = shear modulus of elasticity, N/mm^2 Kw = Wahl factor τs = direct shear stress, N/mm^2 τmax = total shear stress, N/mm^2

Where:

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