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• 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.
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• 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.
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© Goodheart-Willcox Co., Inc.
• Explain the importance of CAD file management and identify common storage techniques.
• List different types of CAD software and their applications.
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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
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Computer Graphics and CAD
• First used for aerospace design in 1950s• Prior to emergence of 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
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© Goodheart-Willcox Co., Inc.
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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Computer Graphics Programs
• Classified according to types of images created– Vector objects– Raster objects
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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
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Raster Objects
• Also called bitmap graphics• Number of pixels defines resolution• Modified using an image editing program
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Vector and Raster Images
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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
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CAD Drawing Display
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File Management Commands
• New• Open• Close• Save• Save as
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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)
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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
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Basic CAD System Functions
• Coordinate systems• Drawing aids• Layers and linetypes• Blocks
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Coordinate Systems
• Used to define coordinates
• World coordinate system is most basic system– Based on Cartesian
coordinate system
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2D Cartesian Coordinates
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Coordinate Entry Methods
• Absolute coordinates• Relative coordinates• Polar coordinates
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Absolute Coordinates
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Relative Coordinates
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Polar Coordinates
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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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Drawing Aids
• Grid• Snap• Object snap• Orthogonal mode
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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
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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
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Drawing Setup Functions
• Specify drawing unit format• Determine drawing scale and sheet size• Create layers• Save common user settings in a template
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Object Drawing Commands
• Line• Circle• Arc• Ellipse• Polygon
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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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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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© Goodheart-Willcox Co., Inc.
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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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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Drawing Polygons
• Polygon command typically used– Enter number of sides– Specify center point– Inscribe or circumscribe the polygon– Enter radius
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Editing and Modifying Commands
• Move• Copy• Rotate• Scale• Undo• Erase
• Array• Mirror • Fillet• Trim• Extend
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Moving Objects
• Move command typically used– Select object or objects to move– Specify base point for selection set– Specify displacement point
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Copying Objects
• Copy command typically used– Select object or objects to copy– Select base point– Specify displacement point– Multiple option copies same selection to more than
one location
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Rotating Objects
• Rotate command typically used– Used to change angular position of object– Select object or objects to rotate– Specify base point– Specify angle (clockwise or counterclockwise)
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Scaling Objects
• Scale command typically used– Used to reduce or enlarge objects by specified scale
factor– Select object to scale– Select base point– Specify scale factor
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Undoing Operations
• Undo command typically used– Used to “undo” previous action– Allows for undoing multiple actions in reverse
sequence
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Erasing Objects
• Erase command typically used– Used to remove unwanted objects quickly– Select objects to erase– Use Undo command to restore erased object
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© Goodheart-Willcox Co., Inc.
Arraying Objects
• Array command typically used– Used to copy and orient multiple objects in a pattern
• Use rectangular array for rectangular orientation– Enter base point, number of rows, number of
columns, and spacing
• Use polar array for polar orientation– Specify center point, number of objects, and angular
value determining amount of rotation
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Mirroring Objects
• Mirror command typically used– Used to create symmetrical objects by creating
mirrored copy of object– Select object to mirror– Specify mirror axis– Keep or delete original object
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Creating Rounded Corners
• Fillet command typically used– Used to create round or fillet– Set radius– Select entities forming intersection
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Creating Angled Corners
• Chamfer command typically used– Used to create chamfer– Set chamfer distance– Select two lines
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Trimming Lines
• Trim command typically used– Used to clean up line overlaps– Specify cutting edge– Select object to trim
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Extending Lines
• Extend command typically used– Used to lengthen object to meet edge– Specify boundary– Select object to extend
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Display Commands
• Zoom 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
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Making Measurements
• Measure Geometry command typically used to calculate common measurements– Linear distances
• Select two points
– Area and perimeter calculations• Select object or pick points defining the area
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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
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Help System
• Provides user help• Accessed with Help command • Organized into documents and references• Includes search functions and question-and-
answer tools
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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
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© Goodheart-Willcox Co., Inc.
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 wrapup– Ensure that files can be accessed in future– Use standard naming, organization, and backup
practices
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CAD System Components
• Computer• Monitor• Keyboard• Pointing device• Output device• Software
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CAD Software
• Type used depends on specific application– 2D drawing– 3D modeling– Mechanical drafting and manufacturing– Advanced rendering and animation
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CAD Modeling Programs
• Used to construct 3D models• Classified by modeling method
– Solid modeling– Surface modeling– Parametric modeling
• Often provide rendering capability
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Solid Modeling
(Designed with Solid Edge from Siemens PLM Software)
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Surface Modeling
(Discreet, a division of Autodesk)
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Parametric Modeling
• Allows modification of parameters during construction
• Used for assembly modeling in mechanical drafting and engineering applications (Designed with Solid Edge from Siemens PLM Software)
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Computer-Aided Design/Computer-Aided
Manufacturing (CAD/CAM)• Computer numerical control (CNC) machines
control manufacturing processes• Computer data input to machine controls
movement of machine tools• CAD-generated drawings supply tool data
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© Goodheart-Willcox Co., Inc.
Rendering Program
• Used to create realistic displays of models with special effects– Lighting– Materials– Environmental settings
• Requires greater computing power to perform necessary calculations
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Animation Program
• Used to assign movement parameters for frame-by-frame animations
• Used for higher-end applications– Architectural building tours– Film special effects– Medical imaging
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What are coordinates?
Points representing units of real measurement from a fixed point.
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When using relative coordinates, objects are drawn using coordinates in relation to the _____.
last coordinate specified
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How does orthogonal mode simplify the task of drawing horizontal and vertical lines?
The movement of the cursor is confined to horizontal and vertical movement in relation to the drawing plane.
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What are layers?
Layers are user-defined object settings that can be displayed or “turned off” to distinguish the different types of content in a drawing.
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An ellipse has a center point, a(n) _____ axis, and a(n) _____ axis.
major, minor
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What two types of arrays can be created with the Array command?
Rectangular and polar arrays
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The Mirror command is useful when drawing _____ objects.
symmetrical
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The _____ command can be used to restore an object that has been erased unintentionally.
Undo
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Which of the following is not an object drawing command?
A. Line
B. Properties
C. Circle
D. Arc
B. Properties
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Name the three most common types of CAD modeling.
Solid modeling, surface modeling, and parametric modeling
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What is parametric modeling?
An advanced form of modeling that allows object dimensions, or parameters, to be modified during the construction of a model.
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How does CAD/CAM combine CAD with automated manufacturing operations?
After a part is drawn in a CAD program, the design data is calculated by the program. The computer data is input to the CNC machine to control the movement of machine tools.
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© Goodheart-Willcox Co., Inc.
• Absolute coordinates– Coordinates located in relation to the coordinate
system origin (0,0,0).
• Array– An orientation of copied objects in a rectangular or
polar pattern.
• Assembly– A functional mechanism made up of multiple
components, referred to as parts.
• Attributes– Text strings of information about related block symbols,
such as product numbers, sizes, or materials.
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• Blocks– Predrawn objects designed for multiple use in drawing
projects.
• Cartesian coordinate system– A system in which coordinate points are located using
the X, Y, and Z axes.
• Chamfer– An angled cut made to remove the “corner” of two
perpendicular surfaces.
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• Computer-aided design/computer-aided manufacturing (CAD/CAM)– A type of manufacturing in which machining data is
generated from CAD drawings and used by computer numerical control (CNC) machines.
• Coordinates– The positions or locations of points along the X, Y, and
Z axes. In a CAD system, the points represent units of real measurement from a fixed point.
• Fillet– An arc representing an inside rounded corner.
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• Grid– A network of uniformly spaced points used to
determine distances.
• Layers– User-defined object settings that can be displayed or
“turned off” to distinguish the different types of content in a drawing.
• Linetype– A user-defined object setting used to describe a line
definition in the Alphabet of Lines.
• Object snap– A function that allows the cursor to be “snapped” to
specific locations on an object.
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• Orthogonal mode– A drawing mode used to draw horizontal and vertical
lines by confining the cursor to horizontal and vertical movement.
• Parametric modeling– A type of 3D-based drawing in which changes to object
parameters during the modeling process affect the entire model.
• Pixels– Tiny shapes of data making up a raster image. Also
called picture elements.
• Polar coordinates– Coordinates located at a given distance and angle.
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• Raster objects– Objects made up of pixels. Also known as bitmap
graphics.
• Relative coordinates– Coordinates located in relation to the last point
specified (or the origin, if a previous point has not been specified).
• Rendering– A highly realistic representation of a model with
lighting, shadows, and other visual effects applied.
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• Resolution– A term used to describe the visual quality of a raster
image, determined by the number of pixels making up the image.
• Round– An arc representing an outside rounded corner. See
also Fillet.
• Scanner– A computer hardware device used to convert a hard
copy image into digital form.
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• Schedule– A chart or table used to list manufacturing and
purchasing information about parts and products on a drawing.
• Snap– A function that allows the user to align or “snap” the
cursor to specific increments in an invisible grid.
• Solid modeling– A type of 3D-based drawing used to create solids
(objects that represent the entire mass of an object).
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• Surface modeling– A type of 3D-based drawing used to create surface
models (objects that have an outer “skin” to represent exterior surfaces).
• Symbol library– A collection of related drawing symbols.
• Template– A saved set of configurations used to start a drawing
file.
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• User coordinate system– A relative drawing configuration enabling the user to
orient a drawing plane to a specific surface, typically used in 3D drawing.
• Vector objects– Objects made up of lines and arcs, defined with point
coordinates in space.
• World coordinate system– A system for locating points using Cartesian
coordinates on the XYZ axes in relation to the 0,0,0 origin.