Compression Springs
Cylindrical coil springs that work under axial compressive load. We manufacture them to original dimensions across the 0.20–40 mm wire range, with closed and ground end options and galvanised finish.
How compression springs work
A compression spring is coiled with a gap between its turns and produces a counter force when compressed along its axis. Despite appearances the wire does not bend, it twists — the whole load turns into shear stress in the cross-section. This is why the shear modulus is used and the spring rate is found from k = G·d⁴ / (8·Dm³·n).
The fourth power in that relation is the detail that misleads most often in the field: enlarging the wire diameter by only ten per cent stiffens the spring by roughly forty-six per cent. Changes made on the idea of "the same spring, slightly thicker wire" therefore give a far stiffer spring than expected and strain the mechanism.
Five dimensions define a compression spring: wire diameter, outside diameter, free length, number of active coils and end form. The first four set the force; the fifth sets how the spring seats. A closed and ground end seats the spring square to the surface and centres the load, while an unground end lets it lean under load. Solid length — the length the spring takes when fully compressed — is about (n+2)·d on a closed-end spring, and if the installation gap falls below that value the spring is permanently crushed.
The best indicator of manufacturability is the spring index: the ratio of mean diameter to wire diameter, C = Dm/d. Below four the wire is overstrained during coiling; above twelve coiling becomes unstable and the spring tends to buckle. The calculator on our home page warns you when your figures fall outside this band, so you can correct the dimensions on screen without waiting for a quotation.
Failure in a compression spring usually begins not with breakage but with a loss of free length. A spring working above the permissible shear stress settles a little on every cycle; its force drops and the mechanism loses its setting. The safety factor therefore answers not only "will it break" but also "for how many seasons will it give the same force". If tempering after coiling is skipped, that same settling happens on the very first load.
Dimensions we need for a quotation
If you have the values below, no sample is required. Anything missing can be filled in with a photograph of the old spring taken next to a ruler.
| Dimension | What it means |
|---|---|
| Wire diameter · d | The diameter of the wire the spring is coiled from. The most influential dimension; it enters the relation to the fourth power. |
| Outside diameter · Dd | The outer measurement of the coil, chosen to suit the bore. Mean diameter Dm = Dd − d. |
| Free length · L₀ | End-to-end length of the spring with no load applied. |
| Active coils · n | The number of load-carrying coils. On a closed-end spring this is the total coil count minus two. |
| End form | Closed and ground, closed unground, or open end. This determines how the spring seats. |
| Coil direction | Right or left hand. Nested spring pairs are wound in opposite directions. |
Compression Springs calculator
Enter your dimensions and we will return the spring rate, solid length and spring index instantly — with a warning if the index leaves the healthy band.
Photographs from production
Which machine groups use it
Springs of this type appear in the following groups in our catalogue, each listed in detail on its own page.
How it is made
Every step after coiling happens in our own plant; nothing is outsourced. This shortens lead times and keeps quality responsibility in one pair of hands.
CNC coiling
Formed across the 0.20–40 mm wire range.
Tempering
Stress is relieved; elasticity becomes permanent.
End grinding
Seating faces are flattened on compression springs.
Galvanising
Surface protection against corrosion.
Packing
Domestic and export logistics included.
Frequently asked questions
What is the difference between a compression and an extension spring?
A compression spring works by being pushed together, an extension spring by being pulled apart. A compression spring has a gap between its coils and its ends are usually ground; an extension spring has closed coils and a hook at each end. The spring rate relation is the same for both.
How is solid length calculated?
On a closed-end compression spring it is about (n+2)·d: the end coils are added to the active coils and the total is multiplied by the wire diameter. If the installation gap falls below this figure the spring closes solid and is permanently crushed.
How much stiffer does the spring get if I increase the wire diameter?
The spring rate varies with the fourth power of wire diameter. A ten per cent larger wire makes the spring roughly forty-six per cent stiffer. Wire diameter is therefore the last adjustment to reach for; coil count and diameter are considered first.
Why does the spring index matter?
The spring index C = Dm/d indicates manufacturability. Below four the wire is overstrained during coiling; above twelve coiling becomes unstable. The healthy band is 4–12, and the calculator warns you when you leave it.
Is end grinding necessary?
If the spring must seat square on a flat surface and centre the load, yes. An unground end lets the spring lean under load. End grinding is carried out in our own plant.
I have no sample — can you produce from dimensions alone?
Yes. Given wire diameter, outside diameter, free length, active coil count and end form, no sample is needed. Sending these values through the quote form is enough.
Other spring types
Cannot find the spring you need?
We produce to your dimensions in the 0.20–40 mm wire range, with no tooling dependency. A sample, a technical drawing, or simply a photograph of the old spring is enough.
Fill in the quote formOr call us directly: 0850 840 54 17