A spring can fit in the available space while leaving an unresolved working-travel question.
Name the three lengths
Lee Spring distinguishes free length and solid height. Solid height describes the coil-contact geometry, not a universal recommended operating position. Primary reference: Lee Spring compression-spring geometry.
Record free length, the intended minimum working length and the applicable solid-height basis. Keep tolerances and any supplier-defined working restrictions with those values. A free-length match alone does not show that the proposed motion has sufficient defined space throughout its travel.
A hypothetical space budget
Assume a fictional free length of 50 mm, solid height of 20 mm and minimum working length of 28 mm. Nominal compression at that position is 22 mm, while the nominal distance above solid is 8 mm. Those are geometry calculations, not evidence that 8 mm is an acceptable reserve or that all 30 mm of theoretical compression is usable.
Put the values and their definitions in separate worksheet columns. Add actual dimensional ranges and the documented working requirement when available. No example dimension belongs to HM, and no operating stroke is prescribed from the arithmetic.
Review the assembled range
The assembly should define its spring positions through all intended modes and relevant variations. Ask how those positions relate to the selected spring's actual operating basis, not merely to a nominal catalog free length.
If a replacement changes end form, wire geometry or the stated solid height, retain that difference in the review. A part that looks the same at rest may not preserve the original travel condition. The useful purchase output is a named length-and-position budget, with the component's working restrictions visible rather than treating maximum coil closure as a target.
Customer Questions
Does fitting the free length prove adequate travel?
No. Working positions and solid-height context also matter.
Is solid height a universal recommended working length?
No. Use the actual spring's documented operating basis.
What can change even if free length matches?
Rate, end form, solid height and other properties can differ.
Primary References
These references support the technical principles discussed in this guide. The worked examples and review questions are educational.
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