How to find the right Mechanical Constant Force Springs AI guide
Written by an AI model from its trained knowledge.
What the AI looks for in Mechanical Constant Force Springs
- Rated force
- Choose the force the spring delivers at working extension. Do not size it from the force at the very start of the pull, which is lower. Force builds over the first part of the extension and then stays roughly flat. A spring sized from early readings will be too strong in use.
- Usable extension
- Treat full force as starting after roughly 1.25 coil diameters of extension. Leave at least a turn or so still wrapped on the drum at full travel. Pulling the spring off its last wraps loses the constant-force behavior and puts stress on the anchor point.
- Drum or mandrel diameter
- Use a drum about 10–20% larger than the spring's free inner diameter, as manufacturer catalogs recommend. A drum that is too small lets the coil slip or bind. One that is too large lowers the force and raises stress.
- Cycle life rating
- Match the catalog cycle-life class to your duty. Standard designs suit occasional motion. For counterbalances that move constantly, specify a high-cycle design. Fatigue life varies widely with stress level. A spring that is fine in a drawer can fail quickly in a moving machine axis.
- Material
- Use 301 stainless for most uses. Choose a specialty alloy only for high heat, magnetic sensitivity or corrosive environments. 301 stainless is the standard strip for constant force springs and resists corrosion well.
- End attachment
- Confirm the outer-end feature (hole, slot or tab) matches your fastener size and load path. Most field failures start at the anchor, not in the body of the coil.
Brands that matter
- Vulcan Spring: A constant force and power spring specialist that publishes detailed sizing and cycle-life data.
- John Evans' Sons: A long-running maker of constant force, power and flat strip springs, including custom work.
- Lee Spring: Stocks constant force springs alongside its broad catalog of standard springs.
- Associated Spring Raymond: An industrial supplier of stock and engineered springs.
What to avoid
- Unbranded springs with no published force, extension or cycle-life data.
- Mounting the coil on a fixed pin with no drum or bushing, which causes wear and erratic force.
- Using one spring at its maximum rated force in a safety-critical counterbalance. Consider two springs in tandem for redundancy.
- Bending or kinking the strip during installation, which leaves a permanent weak point.
Questions
Why is the force lower at the start of the pull?
The spring needs some extension before its curvature reaches steady state. Full rated force starts after about 1.25 coil diameters of travel.
Can I stack springs for more force?
Yes. Laminated (nested) springs or springs mounted side by side add force roughly in proportion. Follow the maker's guidance on drum width and alignment.