AutoCAD Inventor :: Variable Pitch Helix By Equation Curve

You can create a variable pitch helix by using the Equation Curve feature introduced in Inventor 2013.

Create a new 3D Sketch. Start the Equation Curve command.

Here are equations that I use to create helical curves. Many other variations exist.

Cartesian coordinates:

x(t) = radius * sin(360 * num_turns * t) 
y(t) = radius * cos(360 * num_turns * t)
z(t) = height * t

[Code]....

When you sweep a profile along a helical path, use the plane normal sweep (instead of perpendicular sweep) to orient profiles suitable for coil or spring.  In the example below, the sweep path is a constant radius, variable pitch helix.