Conical springs don't have a rate: they have a curve

Ask for the rate of a conical spring and the honest answer is: it depends where you are in the stroke. Unlike a cylindrical spring, whose spring rate is one number, a conical spring stiffens continuously as it compresses. Designing with a single rate value means using an average that only holds at the very start of travel.

The reason is geometric. Each coil's stiffness depends on the cube of its diameter: a coil with twice the diameter is eight times softer. In a conical spring the large coils do almost all the work at first, which is why they are the first to bottom out. Every coil that lands leaves the game, and the survivors are the smaller, stiffer ones: the rate climbs.

The load-deflection curve

The real behavior is a curve: a nearly linear initial segment followed by progressive stiffening up to solid height. Our calc engine models it by discretizing the spring body along the diameter profile: each element has its own stiffness and its own gap, and the model tracks who has landed at every load level.

The result shows up in the studio as a true curve on the load-deflection chart, with the point where the first coil bottoms reported in the engineering results. Working positions, simulation and export all ride the same curve: there are no two versions of the physics.

The side effect that works in your favor: stress shielding

A counterintuitive detail: when a coil bottoms, its stress freezes. It no longer deflects, so it no longer accumulates stress, however high the load goes. That means the large coil, which looked like the limiting element, often lands before reaching the allowable stress and drops out of the equation.

In practice, the safe load of a conical spring can be much higher than a naive largest-coil calculation suggests. The progressive model captures that shielding: the limit becomes the first coil that reaches allowable while still active, or the solid stack itself.

Why choose conical, barrel or hourglass

• Natural progressive rate: soft early in the stroke, firm at the end, with no special pitch zone.
• Lateral stability: the variable profile braces the spring against buckling far better than a slender cylindrical.
• Reduced solid height: conical springs with nesting coils can pack down to a few wire heights.
• Variable natural frequency: a rate that changes along the stroke spreads resonance, useful in dynamic applications.

Designing with the whole curve

With the full curve available, the right questions become easy: what is the load at 70% of travel? Where does the first coil land? How much margin sits between the working point and the stiffening? The studio answers with numbers and shows it in 3D, including deflected-geometry export with the large coils packing first, exactly as the physical spring does.