- Coordinates for 3D CAD Modeling
- Geometric Entities
- 4.1 Manually Bisecting a Line or Circular Arc
- 4.2 Drawing Tangents to Two Circles
- 4.3 Drawing an Arc Tangent to a Line or Arc and Through a Point
- 4.4 Bisecting an Angle
- 4.5 Drawing a Line through a Point and Parallel to a Line
- 4.6 Drawing a Triangle with Sides Given
- 4.7 Drawing a Right Triangle with Hypotenuse and One Side Given
- 4.8 Laying Out an Angle
- 4.9 Drawing an Equilateral Triangle
- 4.10 Polygons
- 4.11 Drawing a Regular Pentagon
- 4.12 Drawing a Hexagon
- 4.13 Ellipses
- 4.14 Spline Curves
- 4.15 Geometric Relationships
- 4.16 Solid Primitives
- 4.17 Recognizing Symmetry
- 4.18 Extruded Forms
- 4.19 Revolved Forms
- 4.20 Irregular Surfaces
- 4.21 User Coordinate Systems
- 4.22 Transformations
- Key Words
- Chapter Summary
- Skills Summary
- Review Questions
- Chapter Exercises

## 4.18 Extruded Forms

** Extrusion** is the manufacturing process of forcing material through a shaped opening (Figure 4.69). Extrusion in CAD modeling creates a 3D shape in a way similar to the extrusion manufacturing process. This modeling method is common even when the part will not be manufactured as an extrusion.

**4.69** Extruded Shape. *Symmetry and several common geometric shapes were used to create this linear guide system. The rail in (a) was created by forcing aluminum through an opening with the shape of its cross section. The extruded length was then cut to the required length. The solid model in (c) was created by defining the 2D cross-sectional shape (b) and specifying a length for the extrusion. (Integrated configuration of Integral V™ linear guides courtesy of PBCLinear.)*

To create as shape by extrusion, sketch the 2D outline of the basic shape of the object (usually called a profile), and then specify the length for the extrusion. Most 3D CAD systems provide an Extrude command. Some CAD systems allow a taper (or draft) angle to be specified to narrow the shape over its length (Figure 4.70).

**4.70** *These CAD models were formed by extruding a 2D outline. Two of the models were extruded with a taper.*

### Swept Shapes

A swept form is a special case of an extruded form. Sweeping describes extruding a shape along a curved path. To sweep a shape in CAD, create the 2D profile and a 2D or 3D curve to serve as the path. Some swept shapes are shown in Figure 4.71.

**4.71** Swept Shapes. *These shapes started as an octagon, a circle, and an ellipse, then were swept along a curved path.*