Modelling a Complex Extension Spring in Spring Calculator Professional

This spring serves as a good example of how Spring Calculator Professional can be used to model more “unusual” springs. It has unusual end fittings, dead coils where these ends are screwed in, and also open coils within the main body.



The requirements given to us by our customer are as follows:

  • Wire details: 5 mm 17/7 precipitation hardened stainless steel to EN 10270-3 1.4568
  • Outside diameter: 40 mm
  • Free length: 250 mm (reference)
  • Working load 1: 220 N at 280 mm
  • Working load 2: 900 N at 370 mm
  • 3 coils each end used to screw in the eyes
  • Body length of 210 mm

Firstly, we need to understand how to deal with the ends. Because they are not a standard hook shape, we will simply model the body of the spring itself by setting the end loop to “No loop”. The free length will be entered as specified; unusually, it is measured relative to the centres of the mounting eyes, but this doesn’t matter as long as we are consistent.

After setting the end loop, we define the dead coils as a total of 6. This same input window allows us to define the body length.


Now we can use the dimensions and loads given to design the spring. We use the “Set Initial Tension, 2 Parameters + 2 Loads/Lengths” input method, because we have everything we need to fully define the spring.


The drawing below confirms the shape of the spring matches the drawing given. The eyes are not present, but the free length shows where their centres would be.


Animating the extension of the spring shows how the dead coils remain inactive as the spring is deflected.


For more information about Spring Calculator Professional head over to our software page or email

Special thanks to G&O Springs for supporting us with the spring information, please take a moment to visit their website