KEVOS® MAKEOS · Springs
Nested Compression Spring Check (Load Share, Stresses, Solid Length, Clearance)
If I nest an inner spring inside an outer one, what load does the pair give at the working length, how is it shared, are both springs within stress, and do they fit together?
Check of two helical compression springs nested one inside the other and compressed together: each spring’s rate, load and corrected shear stress at the working length, solid length and stress at solid (as the compression spring tool), the combined rate and load share in parallel (as the springs in series or parallel tool), the radial clearance between the inner spring’s outside and the outer spring’s inside, and the total load against what you need.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Outer spring | ||
| Wire diameter | mm | Wire diameter of the outer spring. |
| Mean coil diameter | mm | Mean coil diameter of the outer spring. |
| Active coils | coils | Active coils of the outer spring. |
| Inner spring | ||
| Wire diameter | mm | Wire diameter of the inner spring. |
| Mean coil diameter | mm | Mean coil diameter of the inner spring. |
| Active coils | coils | Active coils of the inner spring. |
| Common | ||
| End type (both) | choice | End type of both springs. |
| Shear modulus | GPa | Shear modulus of the spring wire. |
| Unloaded length (both) | mm | Unloaded length of both springs (equal unloaded lengths share the deflection). |
| Working length | mm | Length both springs are compressed to. |
| Allowable shear stress | MPa | Allowable corrected shear stress of the wire. |
| Load needed at the working length | N | Total load the pair must give at the working length. |
| Least radial clearance between springs | mm | Least radial gap between the inner spring’s outside and the outer spring’s inside. |
Method and formulas
- k = G d⁴ ÷ 8 D³ N_a; F = k (L₀ − L_w); τ = K 8 F D ÷ π d³ with the Wahl factor K (as the compression spring tool).
- Parallel rate = k_outer + k_inner; each spring carries its own k × deflection (as the springs in series or parallel tool).
- Radial clearance = [(D_o − d_o) − (D_i + d_i)] ÷ 2; solid length from total coils × wire diameter.
- Example: the pair gives 274.27 N (outer 193.6 N, inner 80.668 N); stresses 291.86 and 311.32 MPa; radial clearance 2.75 mm.
Limitations
- Equal unloaded lengths; unequal lengths make one spring act first.
- Static load; fatigue and buckling of the inner spring need separate checks.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Increase spring force in a fixed space
- Check a nested valve or die spring pair
- Balance stresses between inner and outer springs
Who it is for
- Design engineers
- Toolmakers
- Spring designers
What you get
- Rate, load and stress of each spring
- Combined rate, total load and share
- Solid length and radial clearance
Interpreting the result
- Wind the inner and outer springs in opposite hands so the coils cannot tangle.
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 Nested Compression Spring Check (Load Share, Stresses, Solid Length, Clearance) calculator
