Spring Index: Why it Matters
Torsion Springs
Input results shown will be +/- 10% from middle value
Hint: The closer your min and max inputs are, the more accurate your results will be!
Many times you hear the term spring index being used and it is a common starting point when trying to design a spring or to figure out whether the spring you want to buy is manufacturable, but why? Well, spring Index is basically the relation between the mean diameter and the wire diameter of a spring. It defines the tightness or looseness of the coils. It is one of the factors that determines the strength of a spring, how stressed it can be, and how manufacturable it is.
You can calculate spring index manually or get it from our Spring Creator Calculator that automatically calculates it for you based on a few dimensions. First, you must calculate mean diameter. The formulas are provided below.
Mean Diameter Formula
D = Douter - d
D = Dinner + d
Spring Index Formula
I = D ÷ d
KEY:
- I = Spring Index
- D = Mean Diameter
- d = Wire Diameter
- Douter = Outer Diameter
- Dinner = Inner Diameter
To properly determine what the spring index is, make sure you have the correct measurements and calculations. You can also go into our Spring Creator Calculator, input your spring’s physical dimensions, then click CALCULATE. You will obtain a full analysis of your spring. In it will be your spring index. All you need to do is scroll down to the Physical Dimensions section of your spring analysis.
Spring Index is important because it allows you to:
- Determine how loose or tight your spring is. The spring index is a ratio that tells you how tight a coil is or how loose. The higher the ratio, the looser the coils. The lower the ratio, the tighter the coils. For example: a slinky toy would have a very high spring index.
- Determine the stress of your spring. A low index number means that the spring has a tight index. If the spring has a tight index, it might be under a lot of stress which would make the spring stiffer (stronger) . This can cause the spring to lose elasticity because the coils are so tight.
- How manufacturable your spring is. A very low or very high spring index can be hard to manufacture. More manageable and manufacturable springs fall in the range of 6-12 in spring index. Springs with spring index of around 4-5 or 15-25 may still be manufacturable by Acxess Spring, but at a higher cost.
Buy the Perfect Spring at Acxess Spring
At Acxess Spring we make it easy for you to obtain the custom springs you want. In most cases we can instantly provide pricing and all the specs and information you need, including the spring index. Use our Instant Spring Quote (ISQ) Tool to automatically receive pricing on the spring you want, or use our Online Spring Creator to create the spring design you want and get a full spring analysis. Contact us at: (951) 276-2777 and place your order today.
Invest in precision and quality
Spring Creator 5.0 offers you the possibility to design springs that perfectly fit your needs. Our platform not only allows you to design various types of springs but also provides advanced tools like the Online Spring Force Tester to simulate and evaluate spring performance. Visualize your design in 3D, download detailed blueprints, and get instant quotes. Try it for free and discover why we are the preferred choice of engineers and makers!
Created by Alfonso Jaramillo Jr
President Acxess Spring
Over 40 Years of Experience in Spring Engineering and Manufacturing