Computer-Aided Drafting and Design

7Computer-Aided Drafting

and Design

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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.

• 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.

• Explain the importance of CAD file management and identify common storage techniques.

• List different types of CAD software and their applications.

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 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

Traditional Drafting and CAD

• Principles of drafting are fundamental to both methods

• Knowledge of standards, techniques, and procedures is essential to using CAD effectively

Computer Graphics Programs

• Classified according to types of images created– Vector objects– Raster objects

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

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

Vector and Raster Images

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

File Management Commands

• New• Open• Close• Save• Save as

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

• Publish– Used to “publish” multiple-sheet drawing sets

Basic CAD System Functions

• Coordinate systems• Drawing aids• Layers and linetypes• Blocks

Coordinate Systems

• Used to define coordinates

• World coordinate system is most basic system– Based on Cartesian

coordinate system

2D Cartesian Coordinates

Coordinate Entry Methods

• Absolute coordinates• Relative coordinates• Polar coordinates

Absolute Coordinates

Relative Coordinates

Polar Coordinates

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

Drawing Aids

• Grid• Snap• Object snap• Orthogonal mode

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

Object Drawing Commands

• Line• Circle• Arc• Ellipse• Polygon

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

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

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

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

Drawing Polygons

• Polygon command typically used– Enter number of sides– Specify center point– Inscribe or circumscribe the polygon– Enter radius

Editing and Modifying Commands

• Move• Copy• Rotate• Scale• Undo• Erase

• Array• Mirror • Fillet• Trim• Extend

Moving Objects

• Move command typically used– Select object or objects to move– Specify base point for selection set– Specify displacement point

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

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)

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

Undoing Operations

• Undo command typically used– Used to “undo” previous action– Allows for undoing multiple actions in reverse

sequence

Erasing Objects

• Erase command typically used– Used to remove unwanted objects quickly– Select objects to erase– Use Undo command to restore erased object

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

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

Creating Rounded Corners

• Fillet command typically used– Used to create round or fillet– Set radius– Select entities forming intersection

Creating Angled Corners

• Chamfer command typically used– Used to create chamfer– Set chamfer distance– Select two lines

Trimming Lines

• Trim command typically used– Used to clean up line overlaps– Specify cutting edge– Select object to trim

Extending Lines

• Extend command typically used– Used to lengthen object to meet edge– Specify boundary– Select object to extend

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

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

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 wrapup– Ensure that files can be accessed in future– Use standard naming, organization, and backup

practices

CAD System Components

• Computer• Monitor• Keyboard• Pointing device• Output device• Software

CAD Software

• Type used depends on specific application– 2D drawing– 3D modeling– Mechanical drafting and manufacturing– Advanced rendering and animation

CAD Modeling Programs

• Used to construct 3D models• Classified by modeling method

– Solid modeling– Surface modeling– Parametric modeling

• Often provide rendering capability

Solid Modeling

(Designed with Solid Edge from Siemens PLM Software)

Surface Modeling

(Discreet, a division of Autodesk)

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)

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

Rendering Program

• Used to create realistic displays of models with special effects– Lighting– Materials– Environmental settings

• Requires greater computing power to perform necessary calculations

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

What are coordinates?

Points representing units of real measurement from a fixed point.

When using relative coordinates, objects are drawn using coordinates in relation to the _____.

last coordinate specified

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.

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.

An ellipse has a center point, a(n) _____ axis, and a(n) _____ axis.

major, minor

What two types of arrays can be created with the Array command?

Rectangular and polar arrays

The Mirror command is useful when drawing _____ objects.

symmetrical

The _____ command can be used to restore an object that has been erased unintentionally.

Which of the following is not an object drawing command?

A. Line

B. Properties

C. Circle

D. Arc

B. Properties

Name the three most common types of CAD modeling.

Solid modeling, surface modeling, and parametric modeling

What is parametric modeling?

An advanced form of modeling that allows object dimensions, or parameters, to be modified during the construction of a model.

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.

• 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.

• 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.

• 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.

• 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.

• 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.

• 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.

• 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.

• 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).

• 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

• 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.

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