KEVOS® MAKEOS · Springs
Compression Spring Designer (Two Working Points)
What wire size, coils and free length make a compression spring that gives these two loads at these two lengths?
Synthesis of a round-wire helical compression spring from two working points: the rate and free length they require, the wire diameter that keeps the Wahl-corrected stress at the highest load within your allowable for the chosen mean diameter, active and total coils for the end type, solid length, clash allowance, stress at solid and buckling ratio, as a ready specification.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Working points | ||
| Load at the first point | N | Load at the first (installed) length. |
| Length at the first point | mm | Length at the first point. |
| Load at the second (maximum) point | N | Load at the maximum operating point. |
| Length at the second point | mm | Length at the maximum operating point. |
| Design choices | ||
| Mean coil diameter | mm | Mean coil diameter you can fit (outside diameter = D + d). |
| Allowable shear stress at the maximum load | MPa | Allowable corrected shear stress for the wire material and size at the maximum load. |
| Shear modulus | GPa | Shear modulus of the wire material (79.3 GPa for spring steel). |
| Ends | choice | End type, for total coils and solid length. |
| Clash allowance (share of the deflection) | % | Margin between the maximum operating length and solid, as a share of the deflection from free length. |
Method and formulas
- Rate k = (F₂ − F₁) ÷ (L₁ − L₂); free length L₀ = L₁ + F₁ ÷ k.
- Wire diameter d from τ = K_W 8 F₂ D ÷ π d³, with K_W = (4C − 1) ÷ (4C − 4) + 0.615 ÷ C and C = D ÷ d (solved iteratively).
- Active coils N_a = G d⁴ ÷ 8 D³ k; total coils and solid length from the end type.
- Clash = (L₂ − solid length) ÷ (L₀ − L₂); buckling ratio L₀ ÷ D.
- Example: 100 N at 60 mm and 250 N at 45 mm on a 20 mm mean diameter needs 3.0528 mm wire and 10.762 active coils.
Limitations
- Static or low-cycle duty; fatigue needs a stress range check.
- Round the wire to an available size and re-check with the compression spring calculator.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Design a spring for a valve, clamp or return mechanism
- Turn two load-length points into a spring specification
- Check whether a spring fits the space available
Who it is for
- Design engineers
- Spring buyers
- Product engineers
What you get
- Rate and free length
- Wire diameter and coils
- Solid length, clash, stress at solid and buckling
Interpreting the result
- If the clash allowance is too small, use a larger mean diameter (fewer coils) or a higher-strength wire.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 304–324. Topic reference; no source tables or recommended settings are reproduced.
WORKOS tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
Open the Compression Spring Designer (Two Working Points) calculator
