A helico-volute spring uses a tapered or nested coil form that can provide compact travel and progressive contact behavior. This calculator is a simplified identical-coil active-count illustration, not a force, stress or design model for a real helico-volute spring.
Tension Helico-volute Spring Interactive Calculator
Enter an ideal total coil count, inactive coils for state A and state B, and an entered equal clearance per contacted coil. State B is constrained to have at least as many inactive coils as state A.
Equation Used
- Every ideal active coil has identical compliance and the baseline k0 uses all N coils active.
- Inactive-coil counts are user-entered states, not predicted contact events.
- The clearance input is an equal entered gap used only for the arithmetic sum n_B c.
- Wire or strip geometry, taper, material, stress, friction, hysteresis, contact deformation, end conditions, fatigue and safety are omitted.
Helico-volute Form and Simplified Coil Count
A helico-volute spring uses nested or tapered turns rather than a uniform cylindrical helix. As turns contact or become constrained, the set of freely deforming portions can change.
The animation shows user-entered inactive coils only. It does not calculate the contact sequence of a particular spring or reproduce a dimensioned historical design.
What This Explanatory Calculator Does
NASA spring-design notes give the familiar linear helical-spring relation in which spring constant is inversely proportional to the number of active coils when material and coil geometry are otherwise fixed.
This calculator uses only that inverse-count relation as an ideal illustration. It does not establish the behavior of non-identical helico-volute turns.
Identical-coil Series Idealization
N is the ideal total count, n is the entered inactive count and c is an entered equal clearance. State B is clamped so nB is not less than nA, and at least one ideal coil remains active.
Worked Ideal Count
For N = 5, nA = 2, nB = 3 and c = 2 mm, state A has 3 ideal active coils and rate multiplier 5/3 = 1.67. State B has 2 active coils and multiplier 5/2 = 2.50. The entered closure sum is 3 × 2 = 6 mm.
These are count ratios and an arithmetic gap sum, not a predicted load-deflection curve or safe travel.
Model Boundary
- Calculated: clamped integer active counts, ideal inverse-count multipliers and an entered equal-clearance sum.
- Supporting relation: a uniform linear helical spring's rate varies inversely with active-coil count when all other terms remain fixed.
- Not calculated: tapered geometry, varying mean diameter, rectangular or round section, pitch, nesting, actual contact order, force, deflection, stress, Wahl factor, friction, hysteresis, buckling, set, fatigue, temperature, tolerances, end conditions, capacity, life or safety.
Frequently Asked Questions
Are real helico-volute coils identical?
Usually not. The identical-coil assumption is only an explanatory simplification.
Does the calculator predict when coils contact?
No. Inactive counts are entered directly.
Is the closure sum usable travel?
No. It is only n times the entered equal clearance.
Does the rate multiplier give force?
No. No baseline rate, material or geometry is entered.
Can it calculate spring stress or fatigue life?
No. Those require complete geometry, material, loading and design criteria.
Can it size a railway buffer or coupler spring?
No. It is not a component-selection or safety tool.
References
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