Computer-Aided Drafting and Design CHAPTER 7

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.

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.

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.

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

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

Traditional Drafting and CAD Principles of drafting are fundamental to both methods Knowledge of standards, techniques, and procedures is essential to using CAD effectively Inga Ivanova/Shutterstock.com

Computer Graphics Programs Classified according to types of images created Vector objects Raster objects Goodheart-Willcox Publisher

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

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

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

CAD Drawing Display Autodesk, Inc.

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

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)

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)

Coordinate Systems Used to define coordinates World coordinate system is most basic system Based on Cartesian coordinate system Goodheart-Willcox Publisher

2D Cartesian Coordinates Goodheart-Willcox Publisher

Absolute Coordinates Goodheart-Willcox Publisher

Relative Coordinates Goodheart-Willcox Publisher

Polar Coordinates Goodheart-Willcox Publisher

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 Goodheart-Willcox Publisher

Drawing Aids Grid Snap Object snap Orthogonal mode Direct distance entry

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

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

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

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 Goodheart-Willcox Publisher

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 Goodheart-Willcox Publisher

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 Goodheart-Willcox Publisher

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 Goodheart-Willcox Publisher

Drawing Polygons Polygon command typically used Enter number of sides Specify center point Inscribe or circumscribe the polygon Enter radius Goodheart-Willcox Publisher

Drawing Hatch Patterns Hatch patterns fill closed areas with predefined pattern Patterns represent materials in section view Goodheart-Willcox Publisher

Moving Objects Move command used to reposition objects Select object or objects to move Specify base point for selection set Specify displacement point

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

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)

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

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

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

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 Goodheart-Willcox Publisher

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 Goodheart-Willcox Publisher

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 Goodheart-Willcox Publisher

Creating Angled Corners Chamfer is an angled corner Chamfer command used to create chamfer Set chamfer distance Select two lines

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

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

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

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

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

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

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

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.

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

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.

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

Geometric Constraints Geometric constraints control the geometric relationship between features and objects Constraints added automatically or manually Fully defined means all objects constrained Goodheart-Willcox Publisher

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 Goodheart-Willcox Publisher

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

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 Goodheart-Willcox Publisher

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 Iaroslav Neliubov/Shutterstock.com

Drawing Documentation (Cont.) Goodheart-Willcox Publisher

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

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.

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

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