Copyright Goodheart-Willcox Co., Inc. Chapter 6 Model Extrusions and Revolutions 133 Extrusions along a Path A profi le shape can be extruded along a path to create a 3D solid or surface. The path can be a line, circle, arc, ellipse, elliptical arc, 2D or 3D polyline, helix, 3D solid edge, surface edge, or 2D or 3D spline. Multiple line segments and other objects can be fi rst joined to form a polyline path. The corners of angled segments on the extruded object are mitered, while curved segments are smooth. See Figure 6-3. When open objects, such as lines, arcs, polylines, elliptical arcs, and splines, are used as the profi le, they are converted to a swept surface when extruded along a path. A sweep is a solid or surface that is created when an open or closed curve is pulled, or swept, along a 2D or 3D path. An extrusion is really a form of a sweep. Sweeps are discussed in detail in Chapter 7. To extrude along a path, enter the EXTRUDE command and select the objects to extrude. When prompted for the height of the extrusion, select the Path option. If needed, fi rst enter a taper angle. Then, pick the object to be used as the extrusion path. Objects can also be extruded along a line at an angle to the base object, Figure 6-4. Notice that the plane at the end of the extruded object is parallel to the original object. Also notice that the length of the extrusion is the same as that of the path. The path does not need to be perpendicular to the object. If the path begins perpendicular to the profi le, the cross section of the resulting extrusion is perpendicular to the path, regardless if the path is a straight line, curve, or spline. See Figure 6-5. If the path is a spline or curve that does not begin perpendicular to the profi le, the profi le may not remain perpendicular to the path as it is extruded. If one of the endpoints of the path is not on the plane of the object to be extruded, the path is temporarily moved to the center of the profi le. The extrusion is then created as if the path were connected to the original object, as shown in Figure 6-4. Path A B Figure 6-3. A—Angled segments are mitered when an object is extruded. B—Curved segments are smoothed when an object is extruded. Path A B Figure 6-4. A—An object extruded along a path. B—The end of an object extruded along an angled path is parallel to the original object.