Custom constant force Springs

What Is a Constant Force Spring?

Understanding the engineering behind stable, consistent force delivery across extended displacement ranges

Pre-stressed flat spiral spring delivering nearly constant output force

A constant force spring is a pre-stressed flat metal strip wound into a tight coil. When extended, it unwinds and produces a nearly uniform pulling force throughout its entire stroke. Unlike conventional springs where force increases with displacement, constant force springs maintain stable tension regardless of extension length.

Long stroke capability: Maintains consistent force over distances 10-50x greater than conventional extension springs
Stable force output: Force variation typically under 10% across full working range
Compact packaging: Large force stored in small coil diameter when retracted

Need constant force over long travel? Let's discuss your specific displacement and force requirements.

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Constant Force Spring vs Power Spring

Many engineers confuse these two flat spiral springs. Here's how to choose the right one for your application.

Constant Force Spring

Output TypeLinear Force

Stroke LengthVery Long (meters)

Force Consistency±5-10% variation

Typical UseRetraction, counterbalance

For applications requiring stable pulling force during linear displacement — cable retraction, sliding counterbalance, or continuous tension maintenance.

Power Spring

Output TypeRotational Torque

Stroke LengthLimited rotations

Force ConsistencyTorque decreases

Typical UseEnergy storage, motors

For energy storage and torque output applications — winding mechanisms, motor drives, or rotational energy release requiring stored power.

Not sure which spring type fits your mechanism? Send us your requirements for technical guidance.

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Typical Applications of Constant Force Springs

Where consistent pulling force over long distances solves critical engineering challenges

Cable & Wire Management

Maintain controlled tension on retractable cables, preventing tangling while ensuring smooth extension and retraction without sudden jerking motions.

Prevents cable slack and tangling during operation
Smooth retraction without shock loads
Extends cable service life through consistent tension

Retractable Mechanisms

Power self-retracting systems with predictable force, ensuring components return to home position reliably across thousands of cycles.

Reliable return-to-home positioning every cycle
Eliminates need for motors or complex mechanisms
Predictable force simplifies user operation

Display & Monitor Arms

Provide smooth, effortless positioning of screens and displays across their full range of motion without user fatigue or sudden drops.

Weightless feel across entire adjustment range
Maintains position without drift or sagging
No calibration needed over product life

Don't see your application listed? We've engineered constant force solutions for hundreds of unique mechanisms.

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Constant Force Spring FAQ

Engineering answers to the most common questions about constant force spring design and selection

Constant force springs typically maintain force within ±5-10% across their working stroke. The force is "nearly constant" rather than perfectly constant. Initial extension force may be slightly higher, then stabilizes across the middle 80% of travel. Force consistency depends on maintaining adequate wraps on the arbor — extending until only 1-2 wraps remain causes force drop. Proper design keeps 3-5 wraps minimum at full extension for best force stability.

Extension springs generate force that increases linearly with displacement (F = kx) — pull twice as far, get twice the force. Constant force springs deliver nearly the same pulling force regardless of extension distance. Extension springs are coil helical form, constant force springs are pre-stressed flat strip wound into spiral. Use extension springs when you need variable resistance. Use constant force springs when you need consistent pulling force over long distances, like cable retraction or counterbalancing applications where force must not change with position.

Yes, force output is fully customizable by adjusting strip width, thickness, material, and coil diameter. We can manufacture springs from under 1N to over 500N pulling force. Specify your target force and we'll calculate the optimal spring parameters. For applications requiring very precise force values (±2% or better), we can select-test springs during production. Keep in mind that tighter force tolerances increase cost. Most applications work fine with standard ±5% force tolerance, which provides excellent consistency at lower cost.

Prototype samples: 7-10 business days after design finalization. Production orders: 3-4 weeks for quantities under 1,000 pieces, 4-6 weeks for larger volumes. Rush service available for urgent projects (48-hour tooling, 1-week production) with premium pricing. Lead time starts after design approval and receipt of P.O. Complex configurations requiring special tooling or materials may add 1-2 weeks. We provide realistic delivery commitments upfront so you can plan your production schedule.

Prototype/sampling MOQ: 5-10 pieces for evaluation. Production MOQ: 100 pieces for standard configurations, 500 pieces for highly custom designs requiring dedicated tooling. We're flexible for startups and new product development — contact us to discuss your specific situation. NDA: Yes, we sign NDAs as standard practice before receiving proprietary designs or application details. Your designs and specifications are confidential and never shared with other customers. We can also provide non-compete agreements if your application requires it.

Don't see your question answered? Our engineering team is here to help with technical guidance.

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Send us your constant force spring drawing or performance requirement

Our engineers review every design before production to ensure proper force characteristics, adequate fatigue life, and reliable performance in your application.

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Types of Constant Force Springs We Manufacture

Engineered configurations to match your specific force, stroke, and mounting requirements

By Configuration

①

Single Constant Force Spring

Standard single-layer design for straightforward linear force applications where space allows moderate coil diameter.

Simplest design for reliable force delivery
Cost-effective for medium force requirements

②

Nested Constant Force Springs

Multiple springs concentrically wound to multiply force output within limited space envelope.

High force in compact package
Space-efficient high-capacity solution

③

Opposed Force Springs

Two springs working in opposition for balanced bidirectional force or position holding without drift.

Eliminates position drift or settling
Perfect for counterbalance applications

Need help selecting the right spring configuration? Our engineers can recommend the optimal type for your requirements.

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Key Design Parameters for Constant Force Springs

Critical specifications that determine spring performance and ensure proper fit in your mechanism

Strip Width & Thickness

Defines force capacity and flexibility — wider and thicker strips generate higher pulling force but require larger coil diameter when retracted.

Output Force Range

Target pulling force measured in Newtons or pounds — must account for friction, acceleration loads, and safety factors in your application.

Stroke Length

Maximum extension distance required — determines total spring material length and retracted coil dimensions for packaging.

Cycle Life Requirement

Expected extension/retraction cycles over product life — influences material selection, stress levels, and safety factors in spring design.

Provide your target force, stroke, and space constraints — we'll engineer the optimal spring specification.

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Material Options for Constant Force Springs

Material selection directly impacts force stability, fatigue life, and environmental performance

①

High Carbon Spring Steel

Excellent force stability over life
Superior fatigue resistance
Cost-effective for volume production
Best for indoor, dry environments

②

Stainless Steel 301

Corrosion-resistant for harsh environments
Medical and food-grade approved
Maintains force in wet/humid conditions
Sterilization and cleaning compatible

③

Pre-Tempered Alloy Steel

Optimized hardness and ductility
Minimal force drift under stress
Extended cycle life capability
Consistent batch-to-batch properties

④

Special Coated Strip

PTFE or polymer coatings available
Reduces friction and wear
Quieter operation in mechanisms
Custom coating on request

Specify your operating environment and cycle life needs — we'll recommend the ideal material.

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Manufacturing Process (Constant Force Focused)

Controlled production steps ensuring consistent force characteristics and reliable performance

1

Strip Preparation

Precision-slitting raw material to exact width tolerances, surface inspection for defects that could cause fatigue failure

2

Pre-Stressing & Forming

Cold-winding strip onto mandrel beyond yield point, creating permanent set that generates constant force characteristic

3

Heat Treatment

Controlled thermal cycle stabilizes material structure, relieves forming stresses, locks in force characteristics for long-term stability

4

Force Calibration

Extension testing at multiple points along stroke to verify force consistency meets specification across full travel range

5

Final Inspection

Dimensional verification, visual inspection for surface defects, documentation of test results for traceability and quality records

Every constant force spring undergoes our complete manufacturing and testing process for consistent performance.

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Common Constant Force Spring Design Mistakes We Help Avoid

Engineering pitfalls that lead to premature failure or unsatisfactory performance in the field

!

Force Drop at End of Stroke

Extending spring until only 1-2 wraps remain on arbor causes significant force reduction as curvature changes.

Solution: Maintain 3-5 wraps minimum on arbor at full extension to preserve force consistency

!

Over-Stressing During Assembly

Installing spring with excessive pre-load or insufficient clearance stresses material beyond design limits, reducing fatigue life.

Solution: Design installation with neutral position, allow spring to work within its specified force range

!

Incorrect Mounting Geometry

Sharp bend radii at attachment points or misaligned pull direction creates stress concentrations leading to cracking.

Solution: Provide smooth radii at all bends, ensure spring extends tangent to coil at attachment

!

Ignoring Fatigue Limits

Specifying force too close to material's stress limit sacrifices cycle life — spring may work initially but fails prematurely.

Solution: Design with adequate safety factor based on required cycle life and loading conditions

Our engineers review your design to identify potential issues before production — avoiding costly failures in the field.

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How to Get a Quote

Provide these specifications for accurate pricing and lead time — our engineers review every design before production

Required Information

1

Drawing or Sketch: Layout showing spring installation, mounting method, and available space envelope

2

Required Force & Stroke: Target pulling force (N or lbs) and total extension distance needed in your application

3

Installation Method: Reel mounted, free end pull, or dual attachment — affects spring configuration and mounting hardware

4

Target Life Cycles: Expected extension/retraction cycles over product life — determines material and stress level selection

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