What Is Spring Pitch & How to Calculate It
Spring pitch is an overlooked yet important property directly influencing a helical compression spring’s stiffness and load-bearing capacity. The spring pitch quantifies the axial distance between the centerlines of the helical coil compression spring coils, which are separated when the spring is unloaded. Compression springs store energy by resisting the compressive forces that push the springs together during spring loading.
A few principles will help you understand spring pitch and the related property spring pitch angle and how both impact key spring performance parameters, and we will show you how to calculate both using geometric spring properties. We will highlight how both properties are overlooked yet critical to grasp in spring design and manufacturing disciplines.
What Is Spring Pitch?
Spring pitch is commonly confused with simply the distance between the spring coils; however, this definition is technically incorrect. Spring pitch measures the distance from the center of one helical coil to the center of an adjacent coil along the spring’s axis.
You are likely familiar with the generic term “pitch,” which is commonly used to describe the distance between threads on a machine screw, and the general concept is the same for spring pitch, except the latter represents the spacing between the spring’s helical coils.
What Is Spring Pitch Angle?
The spring pitch angle of a helical coil spring is the angle between the coils and the central horizontal axis of the spring, as visualized when the spring is placed horizontally on a flat surface. As such, the spring pitch angle measures the degree of horizontal tilt in the wire coils as wound into a helical coil.
The spring pitch angle, like spring pitch, is a fundamental geometric property of helical coil compression springs that defines the shape and appearance of spring coils. Additionally, for springs with all other geometric properties in common, the spring pitch angle determines the compressed height of the spring.
One excellent real-world example of observable spring pitch and pitch angles is the large helical coil compression springs within performance automotive suspension systems.
How to Calculate Spring Pitch
The spring pitch is easy to calculate if you know a few basic properties.
For example, one key property in the calculation is the number of inactive coils/wires in your spring. This parameter depends on the spring end type. For example, the helical coils at the end can be either Open or Closed, with additional variations on these two properties as follows:
Closed and Squared
Closed and Ground
Double Closed End
Open Ends
The end type defines one important equation parameter for calculating the spring pitch (p), as shown in the formula below used to calculate the pitch as follows:
Where:
L is the free length of the spring, with is the length of the spring with no load applied
d is the wire diameter
N_a is the number of active spring coils
n is the number of inactive coils and/or wires, which is a function of the spring’s end type with specific examples given as follows:
Closed and Squared Ends: 3 (two inactive coils plus one total inactive wire)
Closed and Ground: 2 (two inactive coils)
Double Closed Ends: 5 (four inactive coils plus one total inactive wire)
Open Ends: 1 (one total inactive wire)
For example, if you want to calculate the spring pitch (p) of a spring with Closed and Ground ends and a free length (L) of 3.15” that has 6 active coils and a wire diameter of 0.12”, the calculation is shown below as follows:
How to Calculate Spring Pitch Angle
After you have calculated the spring pitch (p), you can use this value along with the mean diameter of the spring (D_m) with some basic trigonometry to calculate the spring pitch angle (θ) by using the following relationship.
Example Calculation:
Let’s say we have a helical coil compression spring with the following properties:
Spring Pitch (p): 0.485” (as calculated in the previous example)
Mean diameter (D_m) : 1.242”
D_m can be calculated as follows by using the spring’s Outside Diameter (OD) e spring and wire diameter (d):
D_m= OD - d
For Example: Our spring in this example has an OD of 1.242” and a wire diameter (d) of 0.12”
For Example: Our spring in this example has an OD of 1.242” and a wire diameter (d) of 0.12”
Therefore: D_m = 1.242”- 0.12” = 1.122”
It follows that:
The Impact of Spring Pitch and Pitch Angle on Spring Design and Performance
Spring Pitch and Pitch Angle in Compression Springs
Spring pitch and spring pitch angle impact the following compression spring performance properties as follows:
Spring Rate: The pitch impacts the spring rate (spring stiffness). In general, a larger spring pitch means a reduced spring stiffness.
Compressed Length: The spring pitch and pitch angle determine the compression spring's precise compressed length under load.
Load Capacity: The spring pitch plays a part in the maximum load capacity of the spring because a larger spring pitch means a longer free length of the spring. Thus, a longer fee length decreases the spring rate and, subsequently, the maximum force that can be applied to a spring.
In summary, if all other geometric properties of a compression spring are held constant, the distance between the compression spring coils (spring pitch) and orientation (spring pitch angle) influences the load/deflection profile of the springs.
Spring Pitch and Pitch Angle in Coil/Helical Springs
Spring pitch and spring pitch angle impact the following helical coil spring-specific performance properties as follows:
Stability under Load: The spring pitch angle also impacts the stability of the spring when it is loaded and fully compressed. A smaller pitch generally means a more stable spring under loads; however, a larger pitch angle can stabilize springs with larger pitches.
Dynamic Loads: The spring pitch angle influences the deflection response of the helical coil spring under high cycles of dynamic loading. A larger spring pitch and pitch angle can effectively decrease the total spring compression under dynamic loading conditions.
Performance Optimization: A custom spring pitch and pitch angle are commonly specified to finely tune the spring performance under shock loading conditions or to ensure that a constant spring force is maintained under small changes in loading conditions, such as in an automatic suspension system. As such, the spring pitch and angle adjustments ensure that the spring fits within a small operating envelope and maintains the desired load and deflection characteristics.
In summary, if all other geometric properties of a helical coil spring are held constant, the distance between the coils (spring pitch) and orientation (spring pitch angle) impacts the response of the helical coils under high-frequency cyclic loading conditions. The pitch and pitch angle can be refined to achieve the desired load response profile of the helical coil spring under such conditions.
Why Spring Pitch and Pitch Angle Matter in Spring Manufacturing
As evidenced above, spring pitch and pitch angle must be carefully controlled in manufacturing to mass-produce compression springs that fit their intended application reliably. Furthermore, some helical coil springs have variable spring pitch, increasing the need for manufacturing precision.
Helical coil compression springs are fabricated using either a mechanical coiling machine or an automated CNC coiling machine. Either fabrication method allows for reliable spring pitch and angle control for most spring geometries. However, a good rule of thumb for compression spring manufacturing is that a spring's Outer Diameter (OD) represents the limit of the maximum spring pitch that can be manufactured. Limiting a spring pitch to no larger than 70% of the spring’s Inner Diameter (ID) is recommended.
Furthermore, Century Spring’s state-of-the-art manufacturing technologies feature CAD and CAM tools, allowing us to quickly create digital CAD designs and transfer them to our CNC spring coiling and forming machines for production runs. Our automated production machines can quickly perform complex multi-axis spring coiling and forming operations. These capabilities allow us to reliably produce spring geometry, such as spring pitch and pitch angle, with high precision. These capabilities allow us to serve industries that need large volumes of custom spring designs in accelerated development programs.
Choosing the Right Spring Pitch and Pitch Angle for Your Application
Factors to Consider in Spring Pitch and Pitch Angle Selection
If your application deals with the following factors, calculating the spring pitch and pitch angles and using them to shop may be extremely beneficial as you evaluate helical coil compression springs.
Load Requirements and Performance Optimization
A smaller pitch and pitch angle can increase stiffness and load-bearing capacity for applications requiring the spring to support high loads. Additionally, increasing the spring pitch and pitch angles for springs used in applications that require large shock absorption, such as in heavy machinery, can increase the spring’s ability to absorb repeated, large loads and impacts. An engineered pitch and pitch angle can achieve this performance for springs, even those that must provide a constant force over a tight range of deflections.
Space Constraints
In applications with limited space to fit a spring, tweaking a spring’s pitch and spring pitch angle may enable you to design a spring that fits within a tight design envelope while still meeting your design load and deflection requirements.
Dynamic Loading
For springs used in dynamic applications, such as automotive suspensions, customizing the pitch angle can help optimize the spring’s ability to absorb and dissipate energy from dynamic loads. If the spring needs to handle varying loads, customizing the pitch and pitch angle distributes stress evenly, improving the spring’s durability. Additionally, fine-tuning the pitch and pitch angle is sometimes required to prevent resonance when the spring’s natural frequency matches the frequency of the dynamic load, causing excessive deformations.
Material and Manufacturing Considerations
Furthermore, various materials may inherently necessitate different pitch or pitch angles depending on the mechanical deformation properties of the material. For example, a stainless steel spring may need a pitch or pitch angle different from a comparable phosphor bronze spring with the same OD and wire diameter (d). Custom pitch and pitch angles may also be necessary to accommodate specific manufacturing processes or techniques.
One example of a spring that you may need to optimize is spring pitch and pitch angle. A spring used in a medical device must fit within a compact housing while providing precise force. In such a design case, it’s recommended to minimize the spring pitch and maximize the spring pitch angle within the limits of manufacturability to ensure that the spring is within the intended application and delivers reliable performance without compromising functionality.
Expert Guidance for Optimal Spring Pitch and Pitch Angle Selection
Century Spring brings extensive design for manufacturability (DFM) expertise to your project. We are standing by to answer any questions you may have about spring pitch or spring pitch angles and how they impact your spring design and selection process. We proudly boast an in-house team of spring design experts ready to partner with you today to help you during the earliest parts of your design process to help you choose the best spring with an optimized pitch and pitch angle that will suit your application under static and dynamic load profiles. We are ready to show you how optimizing these spring design details can greatly impact and improve your spring’s performance.
We also have dedicated, high-speed machines that can quickly scale high-quality spring production processes to large part volumes. We also have cutting-edge computational equipment simulation and testing techniques, such as CNC compression self-monitoring and coiling machinery. These capabilities enable us to deliver durable, reliable products across many custom sizes and styles. Our manufacturing services also include complete prototyping and tooling assistance.
Century Spring: Your Partner in Precision Spring Solutions
Century Spring is a quality-first manufacturer with years of experience and innovation in manufacturing stock and custom springs for the most challenging static and dynamic load environments.
We are an ISO 9001-certified spring manufacturer, proudly producing the highest-quality springs that deliver unrivaled system performance even in the most demanding applications and environments. Our state-of-the-art manufacturing capabilities have positioned us to offer unmatched service to industries that need large volumes of customized spring designs in accelerated development programs.
We are committed to minimizing total development time and passing the time savings to you as reduced procurement lead times.
We offer rapid turnaround, shipping, and delivery on over 40,000+ in-stock designs available to ship today, and all of our springs are always made in the USA.