- 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

## Review Questions

What tools are useful for drawing straight lines?

What tools are used for drawing arcs and circles?

How many ways can an arc be tangent to one line? To two lines? To a line and an arc? To two arcs? Draw examples of each.

Draw an approximate ellipse with a major diameter of 6″ and a minor diameter of 3″ . Draw a second approximate ellipse with a major diameter of 200 mm and a minor diameter of 100 mm.

Give one example of a construction technique for CAD that requires a good understanding of drawing geometry.

What is typical accuracy for manually created drawings?

What accuracies may be possible using a CAD system?

Sketch some objects that you use or would design that have right-hand and left-hand parts, such as a pair of in-line skates or side-mounted stereo computer speakers.

In solid modeling, simple 3D shapes are often used to create more complex objects. These are called primitives. Using an isometric grid, draw seven primitives.

What is a Boolean operation? Define two Boolean operations by sketching an example of each in isometric view.

Consider primitives and Boolean operations that could be used to create a “rough” model of each of the items shown below. Using the photos as underlays, sketch primitives that could be used to create items a–d.

a. Handlebar-mount gun rack

b. ACME Corporation reduction gear

c. Ashcroft Model 1305D deadweight pressure tester

d. Davis Instruments solar-powered digital thermometer

Use nothing but solid primitives to create a model of a steam locomotive. Sketch the shapes and note the Boolean operations that would be used to union, difference, or intersect them, or create the model using Boolean operations with your modeling software. Use at least one box, sphere, cylinder, cone, torus, wedge, and pyramid in your design.