Compression Spring Free Length

Free length is an important spring dimension in compression springs, but it is sometimes overlooked. It is important that we consider this part of the spring because it plays a role in the spring rate, spring slenderness ratio, spring compression and max compression spring travel. We will address some of these in this article and point out the role of free length in them.

Definition of FREE LENGTH: The actual length of a compression spring without any sort of load or force being placed on it.

Free Length in Relation to Load or Forced

When a load or force is placed on a compression spring, itslength deflects. Even if the load or force is very small, the length of the spring may travel a few thousandths of an inch. The amount of travel it will deflect depends on the spring’s strength/stiffness and the amount of load being placed on it. The free length of your spring is the length it has as soon as it comes off the machine. It is the length without those loads or forces.

Free Length in Relation to Slenderness Ratio

If a compression spring’s free length is too long in proportion to its diameter, it will be likely to bend or buckle. This is referred to as the Slenderness Ratio . In order to calculate your spring’s slenderness ratio, you must calculate the mean diameter first by subtracting the wire diameter from the outer diameter. The mean diameter is the diameter right in between the outer diameter and the inner diameter; measured from center wire to center wire. Then, you must divide the free length of spring by the mean diameter. The result of this equation will be written as x:1 (x to 1) describing the proportion being made to 1 mean diameter as shown in the example to the right.

Free Length When It Comes to Travel & Force

The free length of your spring, along with other dimensions, can be adjusted to provide more travel and requiring more force. This method is suggested when you need a stronger spring but are under very tight tolerances thus making it difficult to change any other dimension. To know if you’re able to do this with the free length of your spring, visit our online spring calculator and run a design. Look for the values such as True Maximum Travel and Maximum Travel Considering Solid Height in the results of your spring design.

Maximum Travel and Free Length

The maximum travel considering solid height is the amount of travel you’re able to achieve out of your current design with the current free length of spring. The True Maximum Travel, on the other hand, is the travel you would be able to get out of your spring if you made the free length a bit longer. If these two values are the same, you will not be able to make your spring’s free length any longer, but if the True Maximum Travel is greater than the Maximum Travel Considering Solid height, you are able to extend it.

To calculate how much you are able to extend your compression spring’s free length, you must subtract the Maximum Travel Considering Solid Height from the True Max Travel. Once you’ve done this, you’re able to add a value less than or equal to (≤) the result you got from the previous calculation.