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Could the Slenderness Ratio Be Causing Your Spring to Buckle?

How does the slenderness ratio play a factor in causing springs to buckle? It’s all explained here.

Slenderness Ratio Be Causing Your Spring to Buckle? - KB Delta

Compression springs can come under more stress than they are primarily designed to handle. When this happens, it increases the spring’s risk of buckling via lack of proper performance and instability.

Therefore, you need to ensure that buckling doesn’t occur in the compression springs you use in order to prevent an application or product failure.


What is Buckling?

Buckling is a phenomenon that occurs when a spring deforms in a non-axial direction under severe compression. It is often attributed to the substantial free length as the end conditions are not adequate for efficient and even distribution of load along the coil’s circumference.

Compression spring buckling can also occur during deflection, especially for given free lengths, which eventually become too large. This is due to the instability of the spring, often caused by a high slenderness ratio.

During compression, the spring’s instability leads to the trembling of the coils and soon shifts into a non-axial direction. The load that the spring bears can also generate pressure within the shifted coils. This ends up plastering the coils so much that it damages them.

Damaged springs never return to their original states and can no longer provide the pre-designed force they should.


What You Need to Know About the Slenderness Ratio of a Spring

The slenderness ratio is an attribute used to determine a spring’s potential to bend or buckle. In other words, the spring’s slenderness ratio refers to the proportion of the mean diameter to its length.

For instance, a spring’s diameter is more than 3 times its length, causing it to give way and then buckle. However, a spring can have an outer diameter of up to 3 times less than its free length, which provides more than a few ways to curb or limit buckling in springs.

A spring’s free length refers to the length of the compression spring when a load or force is not directly applied to it. Contrary to expectations, a deflection can occur when a load or force has been applied to the spring.

A spring tenderness ratio that is more than 4 indicates the likelihood that the spring will eventually buckle.

This is why it is highly imperative that when choosing or designing a spring, you need to consider spring stability as well as the space or position the spring will occupy.

Therefore, the spring slenderness ratio is a crucial determinant when it comes to defining whether or not the spring will buckle or bend.


How to Know the Slenderness Ratio of Your Spring

You can find out the slenderness ratio of your spring by using 2 simple formulas. But first of all, you need to find out the mean diameter of the spring, i.e., the diameter in the middle of the inner and outer diameters.

Next, divide the free length of the spring by the mean diameter. Any number you get that is greater than 4 indicates that your spring will buckle or bend. For more clarification,

Free length/mean diameter = spring slenderness ratio


  • Spring slenderness greater than or equal to 4 = your spring will, in all likelihood, bend or buckle.
  • Spring slenderness less than or equal to 4 = your spring is not likely to buckle or bend.


Tips to Significantly Boost Slenderness Ratio

Adjusting the spring design can help prevent buckling and bending of your spring. In other words, increasing the slenderness ratio of your spring is possible.

You can do this by adding more coils, decreasing the free length, or increasing the outer diameter. More coils will increase the stability of the spring.

Adjusting the free length and outer diameter will change the overall proportion of the spring’s dimensions, thereby lowering its slenderness ratio.

You can also purchase a compression spring with a more adaptive shape. Barrel springs, hourglass springs, and conical springs can easily help you avoid the buckling of your spring.

The shape of these springs will prevent them from wobbling or bending when severely compressed. This makes such springs the perfect choice for different types of applications.

Another way to improve the slenderness ratio is to place the spring in a hole or insert it into a rod. This helps keep the spring in place and prevents it from getting out of your device.


How to Prevent Your Spring from Buckling

You can prevent your spring from buckling. One of the first ways to do this is by avoiding the use of stock springs.

Stock springs are those springs that you see on the shelf, already designed by a particular manufacturer. You are not responsible for determining the design of stock springs. They are usually stored in an organization’s inventory, ready for use at a moment’s notice.

However, buckling is always an issue with stock springs since they come with longer free lengths.

You can take the following measures if you have no choice but to use stock springs:


  • Place your springs in a tube to prevent them from bending or buckling
  • Add a strong rod right in the middle of the compression spring


You can also opt for custom springs if you want to prevent buckling. Custom springs are those metal elastic devices whose specifications – i.e., length, diameter, rate, etc. – have been maintained based on the needs or wants of a client as well as its application.

In other words, you can determine a custom spring’s parameters. Custom springs also come with special features, often based on the customer’s orders.

The primary goal behind creating custom springs is to ensure compatibility with the mating parts and boost the spring’s properties.

However, when designing a spring, you can easily and directly change its slenderness ratio by taking these measures:


  • Add coils
  • Reduce the free length
  • Increase the outer diameter of the spring


When you put the measures above in place, your spring will never come off its installed location. The only challenge – which is highly negligible or easily dealt with – is that there will be slight friction with the walls of the hole or shaft.



Ensuring that your springs do not buckle or bend under their required loads is highly essential. This is why you should always work with reliable companies with exceptional expertise in spring design.

You should also ensure you avoid making use of stock springs. Stocks springs have an incredibly high rate of application failure. So, avoid them at all costs.

Stick to using custom springs since you can determine their parameters – i.e., diameter, length, etc. – as well as their properties and mating parts with other applications.

Since you know the free length as well as the mean diameter of the spring, you can determine its slenderness ratio.



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