Spring Clarification: What Pitch?

There have been many conversations regarding the proper call out for pitch in a coil spring. It can be tricky, so we want to dive deeper into the topic of spring pitch and provide some reference.

Let’s consider compression springs. The calculations of the parameters for a compression spring require an understanding of its components, which include the type of wire and the wire’s diameter, the space, and of course, the pitch. Each of these factors determine the quality of a compression spring and its performance. Of the various factors, pitch and spacing are two terms that necessitate clarification to provide a better understanding of the structure of a compression spring. Although the terms are related, they define different aspects of a compression spring’s structure.

What is a Pitch Measurement?

The term pitch was derived from screw manufacturing which is the tip of the peak of a screw thread to the next peak of the screw thread. Since round wire does not have a peak or sharp edge, the pitch is measured to the center of the wire. Any time you try to measure pitch on a spring you’re going to end up with different interpretations of where the actual center of the wire is located.

 

 

In screw manufacturing, the pitch determines the effectiveness of a fastener and its strength. It influences the depth and profile of the threads and how well a fastener resists axial and shear loads.

This is especially true on a compression spring. Since there are a variety of interpretations, this can result in an inaccurate measurement error that causes quality rejects for no reason. In order to find the proper and accurate call out for a pitch, there needs to be a measurement taken in the space between the coils.

The Importance of Pitch Measurement

Pitch has a significant impact and effect on the performance of compression springs. The function of compression springs is to absorb force along their central axis. As energy is applied to the spring, the coils move closer together and deform in resistance to the force. Proper measurement of the pitch ensures that there will be no compression spring rubbing, coil to coil.

The rubbing of compression springs can cause extra wear and shorten their longevity. Certain measures can be taken during manufacturing to address the issue of rubbing, each of which protects the integrity and strength of compression springs. One protective method is plating, which coats the wire between the coils. In addition, a reference dimension can be placed on the pitch or space between the coils and add control to the length of the spring. Other possibilities include the use of pre-coated wire or stainless steel wire.

The problem of measuring the pitch of a compression spring is in regard to determining where the center of the wire is located. In certain instances, it can be estimated by measuring the gap or space between the coils and adding one times the wire thickness. Although this is a possible method for determining pitch with compression springs, there are a variety of interpretations as to where the center of the wire of a spring is. Inaccurate measurements and errors that cause unnecessary quality rejects.

More About Compression Spring Design

Compression springs are designed to endure compressive force that reduces their length, a process that is known as deformation or deflection. A well designed and crafted compression spring returns to its original length when the compressive force is removed. This aspect of compression is a critical part of their use. The force that is applied to a compression spring is referred to as stress, which is measured in Pascals (Pa) or pounds per square inch while strain is the change in the length of a compression spring.

Aside from the pitch, several factors are used by engineers when designing compression springs, which include spring rate and load capacity. Spring rate is the load variation per deformation unit while load capacity is the amount of force a compression spring can endure before it buckles or is permanently damaged. Compression springs with a higher spring rate can handle higher loads with less deflection.

As the applied force on a compression spring increases, the amount of displacement increases. This particular factor explains how compression springs store and release energy. The equilibrium position of a compression spring is when it is in its normal length, which is used to determine a spring’s deformation and helps engineers determine how a compression spring reacts when exposed to compression forces.

Although the design and engineering of a compression spring may seem to be a simple process, there are multiple factors that have to be considered. Each element has to be carefully considered to ensure the successful performance of a compression spring. Of the various factors, pitch is carefully examined especially during the manufacturing phase since the coiling of the wire can create variations in the pitch.

One Final Thought On Spring Pitch

Coiling of wire to have super accurate pitch has never been a consistent venture in making springs. Focus on the most important part of springs which is loads. A reference dimension on the pitch/spacing between coils is the best way to call out pitch on drawings.

How Can We Help!

Still struggling with pitch or other design factors? That’s okay! Apex is here to help, and we know springs! Our experienced and highly skilled engineering team is ready to help design the perfect spring for your application.

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