Civil technician R.T. Rinehart sends us a tip describing the Sweep command.
"Many people overlook Sweep, a command for creating complex 3D objects. Sweep allows you to sweep a 2D object along a path and create a 3D solid from it. I use this command frequently when modeling underground pipes and utilities. Once I have a pipe drawn in plan view with a polyline, I simply create a circle that is my pipe diameter and sweep it along the polyline to create the solid.
"To use the command, enter sweep at the command line, select the object you want to sweep, and note the options available at the command prompt. Alignment controls whether the object will be aligned perpendicular to the path before the sweep. Base Point controls the point at which the object will be swept along the line. Scale allows you to enter a dynamic scale that the object will be adjusted to along the course of the sweep (the object will start at the scale you drew it at and end at the scale you specify). Twist works in the same way as Scale, and specifies a twist angle that will be applied to the object during the sweep (the object will start at your current view rotation and end up at the specified angle at the end of the path; excellent for modeling banked roadways or NASCAR tracks). Once you have set your options, simply select a polyline for the path to create the solid. To add further dynamics to the Sweep command, you can use 3D polylines for the path and specify elevation changes along the polyline to allow the object to scale and twist while dynamically changing elevation."
Notes from Cadalyst Tip Patrol: The Sweep command is a powerful 3D object creation tool; with it, you can create very complex and flowing objects. To use Sweep, you need two objects. One is a profile shape — often a closed polyline — and the other is a pathway. The pathway can be many things: a polyline, a line, an arc, a spline, or even a helix. Sweep will create a solid object shaped like your closed profile shape along the pathway. You can sweep multiple objects along a pathway, but they must be coplanar. Also note that when you pick your profile shape to sweep, it is automatically aligned to the object that will be your pathway.