# Thread: Length of a 3D arc on a 2D surface which has been extruded from another arc?

1. ## Length of a 3D arc on a 2D surface which has been extruded from another arc?

Hello,

I'm really stuck on this problem which I need for a project, I do feel like I'm missing something obvious...

Say I have an arc on a plane in 3D Cartesian space, with a radius of $r_{1}$ and an angle of $\alpha_{1}$ (in radians). Say I extruded a surface out of that arc perpendicular to the arcs plane, and then drew another arc on the surface with a radius of $r_{2}$ and angle of $\alpha_{2}$. Both arcs would share an endpoint in the Cartesian space. What is the formula for the length of the second arc in the Cartesian space?

Forgive me if my terminology is a little off, I'm using CAD terminology.