Custom Helical Compression Spring Design

Need Help Designing Your Helical Compression Springs?

At Master Spring, we’ve been manufacturing custom compression springs and helical springs for OEMs for more than 70 years. Learn more about how we can design and manufacture the compression springs for your next application by visiting our Compression Springs page or call us at 708-453-2570 today.

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Common Compression Spring Design Terms

Per Spring Manufacturers Institute Handbook of Spring Design, commonly used compression spring terminology includes:

• d wire diameter
• I.D. Inside Diameter
• O.D. Outside Diameter
• D. Mean coil diameter = (O.D. + I.D.)/2 or O.D. – d
• L_f Free Length = The overall length of a compression spring in the unloaded position.
• P Pitch = The distance from center to center of the wire in adjacent active coils.  Recommended practice is to specify the number of active coils rather than pitch.
• C Spring Index = D/d = ratio of mean coil diameter (D) to wire diameter (d).  The preferred index range is 4 to 12.  Helical springs with high indexes tangle and may require special packaging.  Springs with indexes lower than 4 are difficult to form.
• e_s Squareness = Angular deviation between the axis of a compression spring and a normal to the plane of the ends.  Squareness can be measured by standing a sample spring on end on a horizontal flat plate and bringing the spring against a straightedge at right angles to the plate.  The helical compression spring is rotated to produce a maximum out-of-square dimension es.  Normally squared and ground springs are square within 3º when measured in the free position.
• e_p Parallelism refers to the relationship of the ground ends, and is determined by placing a spring on a flat plate and measuring the maximum difference in free length around the spring circumference.
• Bearing Surface: To improve squareness and reduce buckling during operation, a bearing surface of at least 270º is required.  Squared and ground compression springs are normally supplied with a bearing surface of 270º to 330º.  Additional grinding results in thin sections.

Body Shapes of Compression Springs

Master Spring manufactures four different shapes of compression springs. The parameter that differs from one shape to the next is the spring’s outside diameter.

• Straight Cylindrical Compression Springs (constant outside diameter)
• Conical or Tapered Compression Springs
• Barrel Compression Springs
• Hourglass Compression Springs

3 Compression Spring Design Considerations

Within each of these compression spring shapes outlined above, three additional parameters will determine the shape and, more importantly, the function of the compression spring:

• Ends Closed or Open: The ends can either be closed or open. The most common end types are closed. Closed coil springs have the last 2 coils on each end touching each other so that the spring stands up straight. The last closed coil on each end is called a dead coil because it is not free to deflect under load.
• Ends Ground or Not Ground: For closed coil springs, the ends can be ground or not ground. Ends may be ground to decrease the solid height of the spring and/or to help the spring stand up straight.
• Constant or Variable Pitch: The pitch can be constant or variable. The pitch is the distance from center to center of the wire in adjacent active coils. Recommended practice is to specify the number of active coils rather than pitch. Active coils are the coils which are free to deflect under load. The number of active coils determines the spring’s rate and loads.

Download the Compression Spring Checklist (PDF)