2. Computer-Aided Drafting and Design
CHAPTER 7

3. Objectives
Explain how computer technology is revolutionizing drafting, design, and engineering.
Describe the basic features and operation of a computer-aided drafting program.
Explain the various commands used to create objects in CAD.

4. Objectives Describe the tools used to modify CAD drawings.
Identify the various display functions used in CAD programs.
Describe the typical components in a CAD program help system.

5. Objectives
Explain the importance of CAD file management and identify common storage techniques.
List different types of CAD software and their applications.
Describe the common tools and processes used in parametric modeling.

6. Benefits of CAD Simplifies traditional drafting tasks
Drawing basic shapes
Lettering
Creating views
Maximizes accuracy and proficiency
Setup tools
Drawing and editing commands
Customization methods

7. Computer Graphics and CAD
First used for aerospace design in 1950s
Prior to CAD, design work consisted of 2D drawing production and modelmaking
CAD introduces many benefits:
Eliminates repetitive tasks
Allows more time for creative work
Simplifies process of making 2D and 3D designs

8. Traditional Drafting and CAD
Principles of drafting are fundamental to both methods
Knowledge of standards, techniques, and procedures is essential to using CAD effectively
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9. Computer Graphics Programs
Classified according to types of images created
Vector objects
Raster objects
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10. Vector Objects Created in CAD drawings Made up of lines and arcs
Defined with point coordinates in space
Hard copy images may be converted to raster format with a scanner

11. Raster Objects Number of pixels defines resolution
Modified using an image editing program
Also called bitmap graphics

12. How CAD Works Create CAD model in 2D or 3D form
Use commands to give program instructions
Modify objects with editing and modifying commands
Add dimensions and text
Output drawing to plotter or printer

13. CAD Drawing Display
Autodesk, Inc.

14. File Management Commands
New
Open
Close
Save
Save as
Export
Page setup
Plot
Publish
Hewlett-Packard Company

15. Exporting Files Typically done with the Export command
Used to create files in a different format
Windows Metafile (WMF)
Bitmap (BMP)
Stereolithography (STL)
Portable Document Format (PDF)

16. Plotting and Distribution Commands
Page setup
Used to specify plot device and layout settings
Plot
Used to configure plot device and select type of media
Publish
Used to “publish” multiple-sheet drawing sets
Design Web Format (DWF)

17. Coordinate Systems Used to define coordinates
World coordinate system is most basic system
Based on Cartesian coordinate system
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18. 2D Cartesian Coordinates
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19. Absolute Coordinates
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20. Relative Coordinates
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21. Polar Coordinates
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22. User Coordinate System
Useful for creating drawings in 3D
Orients drawing plane to specific surface
Coordinates are located on drawing plane relative to fixed origin (point on object)
Simplifies 3D drawing process
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23. Drawing Aids Grid Snap Object snap Orthogonal mode
Direct distance entry

24. Layers Used to organize drawing content Named to reflect content
Layer naming conventions observe company or school standards
Similar to overlays used in manual drafting
Assigned colors
Assigned linetypes
Specified in a drawing template

25. Blocks Typically created for commonly used symbols
Windows and doors on architectural plans
Used to save drafting time
Inserted into drawings as needed
Typically stored in a symbol library
May be saved with attributes for use in creating a schedule

26. Drawing Setup Functions
Specify drawing unit format
Determine drawing scale and sheet size
Create layers
Save common user settings in a template

27. Drawing Lines Line command typically used Requires two coordinates
More coordinates may be added within single command sequence
Use proper linetype
Set appropriate layer current before drawing
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28. Drawing Circles Circle command typically used Use appropriate method
Specify center point and radius or diameter
Specify points along perimeter of circle
Enter radius and select two lines or two circles to which circle should be tangent
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29. Drawing Arcs Arc command typically used Use appropriate method
Specify center point, radius, and endpoint
Specify three points along arc
Specify start point, center point, and chord length
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30. Drawing Ellipses Ellipse command typically used
Specify center point, major axis, and minor axis
Elliptical arcs drawn in similar fashion
Specify axis endpoints and start and end angles
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31. Drawing Polygons Polygon command typically used Enter number of sides
Specify center point
Inscribe or circumscribe the polygon
Enter radius
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32. Drawing Hatch Patterns
Hatch patterns fill closed areas with predefined pattern
Patterns represent materials in section view
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33. Moving Objects Move command used to reposition objects
Select object or objects to move
Specify base point for selection set
Specify displacement point

34. Copying Objects Copy command used to reproduce objects
Select object or objects to copy
Select base point
Specify displacement point
Multiple option copies same selection to more than one location

35. Rotating Objects
Rotate command used to change angular position of object
Select object or objects to rotate
Specify base point
Specify angle (clockwise or counterclockwise)

36. Scaling Objects
Scale command used to reduce or enlarge objects by specified scale factor
Select object to scale
Select base point
Specify scale factor

37. Undoing and Redoing Operations
Undo command used to “undo” previous action
Allows for undoing multiple actions in reverse sequence
Redo command used to reverse an action that was undone with the Undo command

38. Erasing Objects Erase command used to remove unwanted objects quickly
Select objects to erase
Use Undo command to restore erased object

39. Arraying Objects
Array command used to copy and orient multiple objects in a pattern
Rectangular array
Base point, number of rows, number of columns, and spacing
Polar array
Center point, number of objects, and angular value
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40. Mirroring Objects
Mirror command creates symmetrical objects by creating a mirrored copy of object
Select object to mirror
Specify mirror axis
Keep or delete original object
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41. Creating Rounded Corners
Round is an arc representing an outside corner
Fillet is an arc representing an inside corner
Fillet command used to create round or fillet
Set radius
Select entities forming intersection
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42. Creating Angled Corners
Chamfer is an angled corner
Chamfer command used to create chamfer
Set chamfer distance
Select two lines

43. Trimming and Extending Lines
Trim command used to clean up line overlaps
Specify cutting edge
Select object to trim
Extend command used to lengthen object to meet edge
Specify boundary
Select object to extend

44. Display Commands Zoom command Pan command
Used to zoom in (to view drawing details) or zoom out (to reduce the view)
Pan command
Used to adjust view in real time without changing magnification
More advanced commands available in 3D drawing programs

45. Making Measurements
Measure Geometry command used to calculate common measurements
Linear distances
Select two points
Area and perimeter calculations
Select object or pick points defining the area

46. Object Property and Drawing Status Commands
Properties command
Used to identify object coordinates and settings assigned to object
List command
Used to list information from drawing database
Status command
Used to identify drawing statistics
Time command
Used to identify current time and drawing time in current session

47. Help System Provides user help Accessed with Help command
Organized into documents and references
Includes search functions and question-and-answer tools

48. File Management and Storage
Establish a logical system of folders to organize files in a project
Use established file naming conventions
Use prefixes to identify project and drawing information
Follow school or company practice

49. Backing Up and Archiving Files
Save and back up work at regular intervals
Follow established protocol
Save work every 15 minutes
Save to a network server
Back up files on a weekly basis
Create file archive during project wrap-up
Ensure that files can be accessed in future
Use standard naming, organization, and backup practices

50. CAD Software Type used depends on specific application 2D drawing
3D modeling
Solid modeling
Surface modeling
Parametric modeling
Provide rendering capability
Model courtesy of SolidWorks Corp.

51. Parametric Modeling Advanced form of modeling
Parameters defined and modified throughout the modeling process
Referred to as “intelligent” models
3D models called parts start as 2D sketches
Basic shape called the base feature
Referred to as feature-based modeling

52. Parametric Modeling (Cont.)
Assemblies are made of multiple parts
Part files linked to assembly file
Changes automatically update
Can be simulated
Working drawings generated from part or assembly files
Model courtesy of SolidWorks Corp.

53. Parametric Modeling Steps
Create 2D sketch to define base feature
Add geometric constraints and dimensions
Create base feature
Create additional features
Repeat steps to create additional parts
Construct assembly model and mate parts
Generate working drawings of assembly

54. Geometric Constraints
Geometric constraints control the geometric relationship between features and objects
Constraints added automatically or manually
Fully defined means all objects constrained
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55. Creating Features
The Extrude tool converts 2D sketches to 3D solids by extending the shape along the Z axis
The Revolve tool creates 3D solids by revolving a 2D sketch around an axis
Child features added to parent base feature
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56. Assembly Modeling
Subassemblies assembled together into larger assembly
Bottom-up modeling
Each part created individually then inserted into assembly
Top-down modeling
Each part modeled within the assembly
Combination of bottom-up and top-down

57. Adding Assembly Constraints
Degrees of freedom (DOF)
Linear movement: X, Y, and Z
Rotary motion: pitch, yaw, and roll
Assembly constraints known as “mates” limit degrees of freedom
Face-to-face
Along the center axis
At an angle
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58. Drawing Documentation
Drawings created from models
Views generated by the CAD software
Base view chosen first, other views projected from base view
Section, auxiliary, detail, isometric, and exploded views
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59. Drawing Documentation (Cont.)
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60. Drawing Documentation (Cont.)
Model dimensions generated by the CAD software
Also called driving dimensions because they “drive” the model geometry
Reference dimensions or drawing dimensions added manually
Bill of materials can be generated automatically based on assembly model

61. Computer-Aided Design/Computer-Aided Manufacturing (CAD/CAM)
Computer numerical control (CNC) machines
CAD-generated drawings supply tool data
Courtesy of Mastercam/CNC Software, Inc.

62. Rendering Programs
Rendering is a highly realistic display of a model with special effects
More computing power needed
Christian Nitz/Shutterstock.com

63. Animation Programs
Used to assign movement parameters for frame-by-frame animations
Used for higher-end applications
Architectural building tours
Film special effects
Medical imaging