Double Helico-volute Spring Mechanism: How It Works, Parts, Formula and Uses Explained

Compression of a double-tapered spring

The lower platen stays fixed while the upper platen moves down. The spring shortens along its axis; the drawing retains the characteristic narrow middle and broad ends. Front and rear portions of the winding are shaded differently so the continuous helix is visible.

The historical illustration identifies a double-tapered compression spring. The calculator treats its axial response as a single spring with an entered overall rate.

The visible cycle is prescribed loading and unloading. It is not a calculation of free oscillation, resonance or damping.

What this calculator estimates

Use a measured or supplier-specified overall spring rate to estimate axial force and stored energy within a range where that rate can reasonably be treated as constant. Enter free height and the intended compression to obtain loaded height.

The calculator does not derive the rate from the illustrated turns. Wire dimensions, material properties and contact between coils are not inputs. The drawing is a form and motion explanation rather than a manufacturing specification.

Constant-rate approximation

With overall rate k in N/mm and compression x in mm, load magnitude is F=kx. Stored energy is U=kx²/2000 joules. Loaded height is H=H0−x, and relative compression is 100x/H0 percent.

These equations assume zero preload and a linear reversible response over the selected range. Actual contact, friction or changing active turns can produce a different load curve. Use an appropriate measured curve when a constant rate does not describe the spring.

Example at 30 mm compression

For an unloaded height of 160 mm and an entered rate of 100 N/mm, compressing the spring 30 mm gives a modeled force of 3,000 N and leaves 130 mm axial height. Stored energy is 45 J; the compression is 18.75% of free height.

Doubling compression doubles force and quadruples energy in this linear model. Changing free height changes loaded height and percentage compression, while force at the same compression remains determined by the entered rate.

Limits of the displayed spring

Hiscox gives a schematic form, not dimensions or a rated load. The animation uses illustrative coil diameter, eight turns and a schematic wire section. Only axial free height and compression are connected to entered dimensions.

This calculation does not establish solid height, coil-contact clearance, buckling resistance, fatigue life or allowable stress. A positive displayed height is not a claim that the actual spring can safely reach that position.

The energy calculation is elastic storage under the linear assumption. It is not energy dissipated per cycle.

Questions about the double helico-volute spring

Does “double” mean an inner spring engages later?

Not in the cited drawing. It shows a double-tapered compression form; no separate delayed engagement is specified.

Where does the spring rate come from?

Enter an overall measured or specified rate for the actual spring and range of interest. The picture does not calculate it.

Why does changing free height leave force unchanged?

At a fixed entered compression and fixed entered rate, F=kx is unchanged. Height controls the geometric height results.

Is the animation a vibration simulation?

No. It demonstrates prescribed compression and return.

What happens at zero compression?

Force and stored energy are zero and the spring stays at its free height.