• The formulas below give good results for moderately stressed springs.

  • A constant factor of 26.4 is used to compensate for cross curvature occurring in the extension form.

  • The spring obeys Hooke's Law as an increment is deflected from curved to straight.

  • The spring is usually not attached to storage drum and at least 1.5 turns should remain on storage drum at full deflection.

  • Caution must be used while using a highly stressed spring like constant force spring as it has an inherently limited fatigue life and its failure can result in harm to equipment or personnel.

Constant Force Spring Nomenclature:

P = Load, lbs

E = Modulus of elasticity, psi

S = Stress, psi

b = Material width, in.

t = Material thickness, in.

Rn= Natural radius, in (Rn= Natural Inside Diameter 2)

R2 = Storage drum radius, in.

Sf= Stress factor


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