How to Draw a Spiral Curve in AutoCADby Darrin Koltow ; Updated February 10, 2017
You can use AutoCad's "Geometry Editor" tool to create a curve between two existing entities. The program enables you enter the specific length and radius of the spiral, so that your draft is as accurate as possible. You can create a spiral curve between any two points, such as the ends of a line or even two other curves.
Click the "Alignment" tab and choose "Modify." Click "Geometry Editor."
Locate the "Alignment Layout Tools" toolbar, and choose "Free Spiral-Curve-Spiral (Between Two Entities)."
Click on the entity where you want the spiral curve to originate, and then click the entity where you want the curve to end.
Set the spiral-out length. Click two points on the drawing to set the length, or manually enter a value. Choose whether you want the curve solution angle to be obtuse or acute.
Set the curve radius. Click two points on the drawing, or press the "D" key and enter a specific radius value.
These steps apply to the AutoDesk AutoCad Civil 3D 2015 version. They may vary for other versions of the software.