What this calculator does
A spiral spring, also called a power spring or clock spring, stores energy in a flat strip wound around a shaft. It is used where many revolutions of torque are needed in a small space. The calculator computes torque, available turns, strip bending stress and the relationship between drum diameter and strip thickness.
Inputs and outputs
Inputs
- Strip thickness and width
- Inside (drum) diameter
- Outside diameter
- Active turns
- Material
- Working torque
Results
- Torque and stored energy
- Turns available
- Bending stress
- Strip length
- Fatigue check
Typical applications
- Clock movements
- Retractable cords
- Cable reels
- Spring motors
- Window and door balances
Design notes
The strip must not exceed the allowable bending stress at the fully wound condition. Keep strip thickness below about one-eighth of the drum diameter to avoid excessive stress and the risk of permanent set.
The interactive calculator interface is currently in Chinese. Enter your values there, or send us the load, travel and space constraints and our engineers will return a checked calculation sheet in English.
Frequently asked questions
Torque or constant force — which spring do I need?
A spiral spring delivers rising torque as it winds. A constant-force spring delivers nearly constant force over its travel. Choose spiral for torque-driven mechanisms and constant force for counterbalance or reel applications.
What limits the number of turns?
Available turns depend on strip length, drum diameter and strip thickness. Thicker strip stores more energy but reduces the turns before the stress limit is reached.
Can the spring be pre-stressed?
Yes. Pre-stressing and heat treatment are controlled in production; specify the working torque range and the number of turns so the strip is set correctly.
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Need this spring manufactured?
Send a drawing, a sample or the parameters from this calculator. We will review manufacturability and reply with a quote and a sample lead time.