John Evans’ Sons is an international leader in constant force spring design and manufacturing. Long deflection, without significant change of force is a key characteristic of constant force springs. As a balancing mechanism, the constant force spring is more compact and lighter than most other methods and can eliminate deadweights, linkages, cylinders and other systems. As a return or retracting mechanism, the constant force spring will provide a smooth, even, uniform load through its entire length of travel (deflection). Constant tensioning or pressure is also a constant force spring attribute. John Evans’ Sons constant force springs are in countless applications including surgical robots and surgical staple devices and the Mars Rovers, Curiosity and Perseverance to name a few.
Custom design, in-house tooling and precision manufacturing as well as a wide and varied stock spring selection, combined with our commitment to quality and on-time delivery, are our strongest selling points.
Consult our Technical Team on constant force springs.
Benefits of Our Springs:
Our constant force springs and assemblies can eliminate costly and complicated motors, decreasing your device size and cost. These types of springs provide:
- Smooth, even, uniform load through entire length or travel (deflection)
- Strong force yield within small spaces
- Extensive linear range
- Small package size
- Ability to easily mount to existing hardware
Product Resources
Design Considerations for Constant Force Springs
There are many design factors that will affect the time and cost needed to manufacture your spring. Therefore, it’s important to work with a manufacturer like John Evans’ Sons that has the knowledge needed in the design phase.
- Mounting Methods: There are several mounting methods. Your application will determine which mounting method is best for your spring’s design.
- Material: The material selection is an important component of the design and project cost. The optimal spring material is often different in high temperature and corrosive environments. Material will certainly affect the design and project cost. High temperatures or corrosive environments will also affect the life of a spring and the required material.
- Diameter and Load: Length, material width, thickness, and coil diameter affect the spring’s load. Increased loads can be obtained by using two or more constant force springs interwound, in tandem, or in other configurations.
All of these, plus other technical considerations, need to be discussed and specified prior to creating prototypes. Our design engineering team can help ensure calculations and configurations are exact in the design phase.
Our springs are most often used in the following industries and applications:
Not sure if constant force springs can provide the right action for your product? Contact John Evans’ Sons for more information.
Spring Comparison Chart
for design parameter comparison (matl. thickness vs. cycle life vs. coiled dia.)
(material: T301 SS, Calculations shown are at 1.0” width, interpolate for other spring material widths)
| Material Thickness | 2,500 cycles | 10,000 cycles | 20,000 cycles | 75,000 cycles | 150,000 cycles | |||||
|---|---|---|---|---|---|---|---|---|---|---|
| Coiled Dia. | Load (lbs.) | Coiled Dia. | Load (lbs.) | Coiled Dia. | Load (lbs.) | Coiled Dia. | Load (lbs.) | Coiled Dia. | Load (lbs.) | |
| 0.002 | 0.15 | 1.3 | 0.17 | 1 | 0.22 | 0.65 | 0.33 | 0.32 | 0.44 | 0.17 |
| 0.003 | 0.22 | 2 | 0.25 | 1.5 | 0.32 | 1 | 0.48 | 0.5 | 0.66 | 0.26 |
| 0.004 | 0.3 | 2.6 | 0.34 | 2 | 0.44 | 1.3 | 0.65 | 0.65 | 0.89 | 0.35 |
| 0.005 | 0.36 | 3.3 | 0.43 | 2.5 | 0.55 | 1.6 | 0.81 | 0.8 | 1.11 | 0.44 |
| 0.006 | 0.44 | 4 | 0.51 | 3 | 0.65 | 2 | 0.95 | 1 | 1.33 | 0.52 |
| 0.008 | 0.59 | 5.2 | 0.69 | 4 | 0.87 | 2.6 | 1.28 | 1.3 | 1.78 | 0.7 |
| 0.01 | 0.73 | 6.6 | 0.86 | 5 | 1.08 | 3.3 | 1.59 | 1.6 | 2.22 | 0.87 |
| 0.012 | 0.87 | 8 | 1.03 | 6 | 1.3 | 4 | 1.91 | 2 | 2.67 | 1.04 |
| 0.014 | 1.02 | 9.3 | 1.2 | 7 | 1.52 | 4.6 | 2.22 | 2.3 | 3.07 | 1.2 |
| 0.016 | 1.16 | 10.6 | 1.37 | 8 | 1.73 | 5.3 | 2.53 | 2.7 | 3.6 | 1.4 |
| 0.018 | 1.31 | 11.9 | 1.54 | 9 | 1.96 | 5.9 | 2.85 | 3 | 4 | 1.56 |
| 0.02 | 1.46 | 13.2 | 1.71 | 10 | 2.18 | 6.6 | 3.2 | 3.3 | 4.44 | 1.74 |
| 0.022 | 1.61 | 14.5 | 1.89 | 11 | 2.37 | 7.2 | 3.48 | 3.6 | 4.89 | 1.91 |
| 0.025 | 1.81 | 16.5 | 2.14 | 12.5 | 2.72 | 8.2 | 4 | 4.1 | 5.55 | 2.18 |
| 0.028 | 2.04 | 18.5 | 2.4 | 14 | 3.04 | 9.5 | 4.48 | 4.6 | 6.23 | 2.44 |
| 0.032 | 2.26 | 20.5 | 2.65 | 15.5 | 3.36 | 10.2 | 4.94 | 5.1 | 6.9 | 2.7 |
CLICK for a larger selection chart, LIVE data & ordering links!
STOCK Constant Force Spring Selection Chart
Order small quantities (click chart shown above).
Large Multi-Leaf (interwound), Highly Specialized End Detail & Sub-Miniature Constant Force Spring Examples
Need Assistance? Consult our Technical Team.
Our Technical Team offer a depth of expertise to assist you with all parts of the process. We are ready to answer your questions in a timely manner and will help you define what you need. We produce custom springs for all purposes, and we are here to work with you on any of your customization needs.
