Calculates Ratio spring diameter to wire diameter
Spring index (C)= Ratio of mean coil diameter to wire diameter (D/d).
Notes
Spring Index in Coil Springs
The spring index is the relationship between the mean diameter and wire diameter. The equation is shown below. This is a very important relationship to consider for manufacturing ease and cost control. As a general rule the index should be above 3 and less than 20. Springs designed outside these limits increase cost and require more tolerance.
Springs with small indexes increase tooling wear and are more likely to require additional processing steps to ensure adequate life. Large index springs often require additional tolerance on both diameter and length.
I =D /d
where I= index, D= Mean Coil Diameter, d=Wire Diameter