Products > Springs
Hourglass (Concave) Springs: Overview, Design & Applications
Hourglass or Concave springs are a type of helical coil compression spring with helical coils that decrease in diameter from the ends to the middle of the spring. In this way, the diameter of the hourglass spring is large at the ends and small in the middle, giving the spring an hourglass shape. The broad base at the ends of the spring provides stability at each end of the spring during applied compression loads. Hourglass springs are similar to Concial Springs, except hourglass springs have wide bases at both ends of the spring.
The hourglass shape allows the coils to telescope down into each other, providing a low compressed height. Hourglass springs have non-linear spring rates that increase as the spring is displaced nearer to the larger helical coils. This is desirable for dynamic applications because the spring provides additional damping resistance as it compresses, which is an ideal property for a spring used in large dynamic loading environments. Hourglass springs are self-centering under compression loads, as the hourglass shape guides compression of the coils about the central axis of the coils, even under offset loads.
Hourglass springs are found in compact applications that require stability control. These applications include medical devices, battery contacts, and electric motors. They are also used as vibration isolation equipment for industrial machinery and equipment, or similar applications.
Century Spring can design custom hourglass compression springs to fit your application’s requirements. All hourglass springs are manufactured to precise dimensional tolerances and small wire diameters to function reliably within compact assemblies.
Custom Hourglass Springs
We bring our decades of design and manufacturing expertise to your unique spring application through custom hourglass springs designed specifically for you. We offer numerous custom hourglass compression spring design options, including custom end sizes, high-strength materials, and wire diameters. We can also show you how to design a custom hourglass spring to self-center your design loads and achieve reliable high-cycle performance of your custom hourglass spring.
We offer additional engineering and design services, such as prototyping. We are eager to partner with you at any stage of development, from the initial design concept to final product procurement.
Custom Hourglass Spring Manufacturing Capabilities
We proudly offer state-of-the-art manufacturing equipment to deliver high volumes of custom hourglass springs. For example, our cutting-edge CNC compression self-monitoring and coiling machinery can manufacture large hourglass springs to fit any design envelope. At the same time, our precision equipment and expert manufacturing team can deliver custom high-quality small hourglass springs with tight dimensional tolerances to suit the most compact applications.
Common hourglass customization options include wire diameter, large outer diameter, small outer diameter, free length, and material. Custom hourglass springs can be designed with variable coil spacing to reduce the compressed spring height and produce nonlinear load deflection characteristics.
Contact our experts to partner with us in developing custom hourglass springs engineered for high-performance applications and environments.
What Our Customers Are Saying
“Terrific customer service agents who are willing to research and find the answer if they don't know. Nice email updates and quick product delivery.”
“I am surprised that a big company like yours would work with us little guys. And Thank You because we don't have another source for springs.”
“The website works really well, that is very important to me to find what I need quickly and accurately.”
Hourglass Spring Information & Resources
Hourglass Spring Applications
Hourglass coil springs are used in many aerospace assemblies, including safety-critical electronic buttons and switch relays. Large hourglass compression springs are also used in high-performance automotive suspension systems because the variable spring rate provides excellent vehicle handling capabilities over large wheel displacements. They used to isolate vibrations in large industrial equipment. Finally, small stainless steel hourglass springs are integrated into medical devices such as surgical instruments or syringe injectors.
Century Spring delivers high-quality, reliable stock and custom hourglass springs for applications in the following industries, making us your trusted partner for any application.
How to Select an Hourglass Spring
Generally, key geometric properties such as the Large Outer Diameter (Large OD) and Small Outer Diameter (Small OD), the largest and smallest circumferences of the helical coil at the ends and middle of the spring, respectively, define the shape of hourglass springs. Choose an hourglass spring with a Large OD that is sufficient to provide the stability you need for your application.
Similar to standard helical coil compression springs, the Spring Rate is the property of a spring that measures the resistance of the spring to compression forces. However, unlike the standard helical coil compression spring, hourglass spring rates are non-linear, increasing as the spring is compressed. The spring rate specification is an average value across the full spring compression for hourglass springs.
You should begin by selecting an hourglass spring that meets your required spring rate and geometry to allow you to calculate the deflection under your application’s design loading conditions. You should then consider the environment in which your spring will operate and your spring’s operational design life requirements to determine if you need a special material or surface treatment to protect against corrosion or fatigue, respectively.
The spring rate your hourglass spring needs will determine the spring’s Wire Diameter, which is the thickness of the metal used to form the helical coils. The thicker the wire diameter, the stiffer the spring, and the higher the loads it can accommodate.
Finally, the Free Length dimension is the vertical height of the hourglass spring measured from the top and bottom surfaces of the spring when it is uncompressed. Your spring’s free length should fit the space envelope of your application.
Typical Tolerances
Century Spring produces all our stock springs to commercial tolerances defined by the Spring Manufacturers Institute (SMI). All listed specification values use the calculated loads and spring rates and the SMI listed geometric tolerance values, which are approximately +/- 10%. However, spring indices values on both the low and high ends will have a larger tolerance range value.
In general, all dimensional tolerance values for hourglass compression springs apply only to the top and bottom of the coils, making this an important consideration if your hourglass spring is to be placed over a mandrel or rod. Additionally, the angular tolerance of the wire at the end of the spring is +/-5 degrees, representing the deviation from the last coil to the perpendicular body axis of the hourglass spring.
Finally, you should note that springs with a coil count less than four are manufactured to the physical dimensions only, meaning the spring rate and maximum rated loads provided for reference purposes only and are not fully certified due to an insufficient number of active spring coils.
If you require additional information, we have conducted extensive empirical studies that have informed the development of tolerance equations for various manufacturing techniques. We have combined these with the best industry standards to create general tolerance ranges for hourglass compression springs.
However, if you contact our design team today, we will be happy to walk you through these calculations to provide general tolerance values for your spring.
FAQs About Hourglass Springs
What makes a compression spring an "hourglass" spring?
You can immediately distinguish between typical straight helical coil compression springs and hourglass or concave springs by their shape. Hourglass springs have a smaller midsection diameter than the top and bottom diameters of the spring, giving the spring its hourglass shape.
How do hourglass springs improve the stability and alignment of my mechanism?
Hourglass springs are inherently stable because of their wide base and narrow midsection. You can think of the stability of hourglass springs in terms of the stability of the pyramid. The wide base allows for a large area to distribute applied loads on the top, narrow portion of the spring. The pyramid shape also gives them a self-centering capability, meaning that offset loads applied at the ends of the spring naturally become aligned to the centerline of the helical coils.
What material should I choose for my hourglass springs?
Considering the corrosion resistance in conjunction with your application's temperature and loading requirements, this is a great place to start when selecting the material. Common hourglass spring materials include music wire, stainless steel, and other metallic alloys.
Do I need a custom design?
We can quickly manufacture standard hourglass springs in many wire diameters and free lengths. However, if you need a custom size that deviates from standard helical coil wire sizes or diameters, you likely need a custom hourglass spring solution.
You can call us today at 800-237-5225 or fill out our Custom Quotation Form to get started on your custom project.
Browse More Compression Springs
You can browse our full selection of compression springs by spring type, filtering by wire diameter, outer diameter, free length, spring rate, and material to get an idea of the options available for your hourglass compression spring.
Why Choose Century Spring
Our Commitment to Quality and Service
Century Spring is a quality-first, ISO 9001 and AS9100D certified, industry-leading spring supplier specializing in stock and custom springs. We are the most trusted name in spring manufacturing, offering products and expertise tailored to all industries.
Our dedicated custom spring development and customer support teams help you navigate critical design criteria such as size, material, surface finish, and end type to find your application's optimal spring solution.
Our experienced product engineers, knowledgeable product quality team, and skilled manufacturing personnel are committed to delivering the highest quality products. Our springs are always made in the USA.
We offer rapid delivery on over 40,000+ in-stock designs available to ship today. You can download CAD models of all our stock springs and wire form products to see how your spring will fit your application before purchasing. Place your order today to take advantage of same-day shipping on stock springs.
Whether you need a stock spring or a custom solution, we are committed to delivering products to you faster than our domestic and international competitors because we understand your design scheduling constraints.
Discover how our commitment to quality and customer satisfaction vastly improves your development process!
Innovation and Customization in Spring Manufacturing
We bring extensive design for manufacturability (DFM) expertise to your project. We also have dedicated, high-speed machines that can quickly scale high-quality production processes to accommodate large volume orders.
Our Manufacturing Services include prototyping and tooling assistance. 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, precision products across many sizes and styles.
Our team will work directly with you to create, refine, and optimize spring designs to fit specific tolerance, performance, and use case conditions. We partner with you to solve your most pressing design challenges.
Get In Touch
Contact Information
Contact us directly today, and let our experts resolve all your technical and sales questions. We can guide you through our stock spring options for each spring type and material.
If you need immediate assistance, you can always reach us at our dedicated phone line to speak directly with our team: 800-237-5225.
Request a Quote and Consultation
If you can’t find the hourglass spring you’re looking for in our catalog, you can always Request a Custom Quotation to partner with us in designing a custom spring specifically for your unique application.
We will follow up with a customized quotation, recommendations, and address any additional questions you may have.