Compression Spring Design Guide

1.) Dimensions and Material Type

The first thing you must do, as shown on our spring calculator, Spring Creator, is set your compression spring’s physical dimensions and specifications. These don’t only include your compression spring’s measurements but also the end types and material type. First, measure your compression spring’s surroundings to make sure that the dimensions you decide upon will not affect the spring when actually being installed. If it is going over a shaft or hole, you must be vigilant on the inner and outer diameters. Make sure you have some clearance between your spring’s coil diameters and the walls of the hole/shaft or other mounting pieces that may intervene with the spring’s deflection in order to avoid damage caused by friction or impact on the coils. It is best for the spring to be pre-loaded so make sure that the free length of your spring is a bit longer than the distance from the base where the spring will be standing to the object that’ll be applying force. The compression spring design formulas to calculate its physical dimensions are provided below as well as how to choose a material type.

End Types

There are several types of compression spring ends types. The most popular ends are closed and squared ends. The other end types provided on our compression spring calculator are closed and grounds ends, double closed ends, and open ends. Changing the end types will affect your spring in stability and even force. This is because changing the end type and keeping the active coils the same will affect the total coil count or solid height. Affecting the coil count could result in force changes as well as specified on the later provided force chart.

Material Types

Choosing the material type of your compression spring is a very important compression spring design process because choosing the wrong material for your spring can either cause your spring not to work in the required environment or unnecessary costs. Unnecessary costs are bound to happen when selecting a material type if you picked an exotic material type while you could’ve used a more common wire type such as Music Wire ASTM A228 or Stainless Steel 302 A313. Your spring not working can be caused by not taking your spring’s environment into consideration when it comes to corrosion, high temperatures, or magnetic fields.

Compression Spring Design Guide Formulas

Outer Diameter: The outer diameter of your compression spring is calculated by adding two wire diameters to the inner diameter.

Inner Diameter + 2 Wire Diameters = Outer Diameter

ID + 2 WD = OD

Inner Diameter: The compression spring’s inner diameter is calculated doing the opposite; subtracting two wire diameters from the outer diameter.

Outer Diameter – 2 Wire Diameters = Inner Diameter

OD – 2 WD = ID

2.) Force and Elasticity

Your compression spring’s force is defined by its spring rate, also known as spring constant. This specification is expressed in load per distance traveled (lb/in or N/mm) which means that your compression spring’s distance traveled will depend on the load you apply and vice versa. The amount of load at a specific distance traveled are your spring’s working loads. Knowing these values will help you determine the spring rate you’re required to have in order for your spring to function as planned. The formula we’ve used on our calculator to calculate compression spring rate is the one provided to the right. As you can see, the spring’s physical dimensions and material type have a lot to do with how strong your spring will be.

Knowing your load and travel doesn’t necessarily mean you’re gonna be able to achieve it, though. Springs have an elastic limit which only allows you to travel a certain distance thus limiting your load as well. There are two different values for travel and load limitations. There is True Maximum Travel and Maximum Travel Considering Solid Height as well as there is True Maximum Load and True Maximum Load Considering Solid Height. These are both related to each other since the distance your spring travels is proportional to its load. True Maximum Travel is a possible amount of travel. This means that you’re able to get that much travel if you were to make your compression spring’s free length longer. The Maximum Travel Considering Solid Height, on the other hand, is the amount of travel you’re gonna get out of the spring design you have now. If the True Max Travel is higher than the Maximum Travel Considering Solid Height, you’ll be able to extend the free length and your compression spring will also be able to travel down to solid height. If they are the same, it means your spring has reached its limit and its free length cannot be extended because you’re already getting all of the travel the spring can achieve with its current dimensions. That would be your compression spring’s maximum compression. The same goes for the True Maximum Load and Maximum Load Considering Solid Height. The formulas to calculate your required rate and working loads are provided below.

Compression Spring Formula Guides

To calculate the amount of rate on a compression spring design based on physical dimensions including material type use the formula provided below:

k = Gd^4 / 8D^3N

Explanation of Symbols:

• d = Wire Diameter
• D = Mean Diameter
• N = Active Coils
• G = Shear Modulus of Material
• K = Spring Constant

G-Value for Common Spring Materials

• Music Wire = 11.5 x 10^6
• Stainless Steel = 11.2 x 10^6
• Phosphor Bronze = 5.9 x 10^6
• Monel = 9.6 x 10^6
• Inconel = 11.5 x 10^6
• Copper = 6.5 x 10^6
• Beryllium Copper = 6.9 x 10^6

Calculate Required Spring Rate

To calculate your compression spring’s rate (k) you must divide your spring’s load (L) by the distance traveled (T).

Rate = Load ÷ Travel

k = L ÷ T

Calculate Working Loads

To calculate your compression spring’s load (L) at a certain distance traveled you must multiply the spring rate (k) by that distance traveled (T).

Load = Rate x Travel

L = kT

Calculate Distance Traveled

To calculate the distance traveled (T) under a certain load, you must divide the compression spring’s load (L) by the spring rate (k).

Travel = Load ÷ Rate

T = L ÷ k