Engineering Graphics as a Language 2 1-1 The Language of Industry 2 Local Area Networks LANs 27 Wide Area Networks WANs and the World Wide Web WWW 27 Cooperative Work Environments 28
Trang 2Engineering Graphics as a Language 2
1-1 The Language of Industry 2
Local Area Networks (LANs) 27
Wide Area Networks (WANs) and the World Wide
Web (WWW) 27
Cooperative Work Environments 28
2-4 Computer-Aided Manufacturing (CAM) 28
Computer Numerical Control 28
Robotics 28
Computer-Integrated Manufacturing (CIM) 29
Review and Assignments 30
3-2 Filing and Storage 36
Filing Systems 36 CAD 37
4-2 Circles and Arcs 51
Center Lines 51 CAD 51 Drawing Circles and Arcs 51 CAD 53
4-3 Drawing Irregular Curves 53
CAD 54
4-4 Sketching 54
Sketching Paper 54 Basic Steps to Follow When Sketching 57
Review and Assignments 58
iii
Trang 3iv Contents
-Applied Geometry 70
5-1 Beginning Geometry: Straight Lines 70
5-2 Arcs and Circles 73
6-2 Arrangement and Construction of Views 92
Spacing the Views 92
Use of a Miter Line 93
CAD 94
6-3 All Surfaces Parallel and All Edges
and Lines Visible 94
6-4 Hidden Surfaces and Edges 95
Holes Revolved to Show True Distance from Center 102
6-15 Intersections of Unfinished Surfaces 103 Review and Assignments 105
Auxiliary Views and Revolutions 132 7-1 Primary Auxiliary Views 132
Dimensioning Auxiliary Views 134
7-2 Circular Features in Auxiliary Projection 135 7-3 Multi-Auxiliary-View Drawings 136
7-4 Secondary Auxiliary Views 137 7-5 Revolutions 140
Reference Planes 140 Revolutions 140 The Rule of Revolution 142 True Shape of an Oblique Surface Found
by Successive Revolutions 142 Auxiliary Views and Revolved Views 143 True Length of a Line 144
7-6 Locating Points and Lines in Space 145
Points in Space 145 Lines in Space 145 True Length of an Oblique Line by Auxiliary View Projection 146
Point on a Line 146 Point-on-Point View of a Line 148
7-7 Planes in Space 148
Locating a Line in a Plane 148 Locating a Point on a Plane 149 Locating the Piercing Point of a Line and a Plane-Cutting-Plane Method 150 Locating the Piercing Point of a Line and a Plane-Auxiliary View Method 1SO
7-8 Establishing Visibility of Lines in Space 152
Visibility of Oblique Lines by Testing 152 Visibility of Lines and Surfaces by Testing 152 Visibility of Lines and Surfaces by Observation 153
7-9 Distances between Lines and Points 154
Distance from a Point to a Line 154 Shortest Distance between Two Oblique Lines 154
7-10 Edge and True View of Planes 157
Planes in Combination 158
7-11 Angles between Lines and Planes 160
The Angle a Line Makes with a Plane 160 Edge Lines of Two Planes 161
Review and Assignments 163
Chapter 8 '.\;>i';· -'~<,, ~
Basic Dimensioning 177 8-1 Basic Dimensioning 177
Dimensioning 177 Units of Measurement 181
Trang 48-3 Dimensioning Common Features 189
Repetitive Features and Dimensions 189
Limited Lengths and Areas 192
Wire, Sheet Metal, and Drill Rod 192
8-4 Dimensioning Methods 192
Rectangular Coordinate Dimensioning
193
8-5 Limits and Tolerances 195
Additional Rules for Dimensioning 200
8-6 Fits and Allowances 201
Fits 201
Description of Fits 201
Interchangeability of Parts 202
Standard Inch Fits 202
Basic Shaft System 205
Preferred Metric Limits and Fits 205
8-7 Surface Texture 208
Surface Texture Characteristics 209
Ribs in Sections 243
Holes in Sections 243
Lugs in Section 243
9-8 Revolved and Removed Sections
243
245
9-9 Spokes and Arms in Section 247 9-10 Partial or Broken-Out Sections 248 9-11 Phantom or Hidden Sections 248 9-12 Sectional Drawing Review 248 Review and Assignments 249
Thread Forms 271
Thread Representation 271
Right- and Left-Hand Threads 272
Single and Multiple Threads 272
Simplified Thread Representation 273
10-3 Common Threaded Fasteners 280
Trang 5Special Tapping Screws 291
Review and Assignments 295
Miscellaneous Types of Fasteners 305
11-1 Keys, Splines, and Serrations 305
Stamped Retaining Rings 312
Wire-Formed Retaining Rings
Spiral-Wound Retaining Rings
Ferrous Metals 341 Cast Iron 341
12-2 Carbon Steel 343
Carbon and Low-Alloy Cast Steels 343 High-Alloy Cast Steels 343
Carbon Steels 343 Steel Specification 343 SAE and AISI-Systems of Steel Identification 345 High-Strength Low-Alloy Steels 348
Low- and Medium-Alloy Steels 348 Stainless Steels 348
12-4 Plastics 352
Thermoplastics 352 Thermosetting Plastics 352 Machining 3S2
Material Selection 352 Forming Processes 354
12-5 Rubber 357
Material and Characteristics 357 Kinds of Rubber 357
Assembly Methods 357 Design Considerations 358
Review and Assignments 359
Forming Processes 364 13-1 Metal Castings 364
Forming Processes 364 Casting Processes 364 Selection of Process 368 Design Considerations 369 Drafting Practices 371 Casting Datums 373 Machining Datums 374
13-2 Forgings 375
Closed-Die Forging 375
Trang 6General Design Rules 376
14-1 Drawing Quality Assurance 398
Simplified Representations in Drawings 402
Installation Assembly Drawings 411
Item List 411
14-7 Exploded Assembly Drawings 412
14-8 Detail Assembly Drawings 413
15-2 Curved Surfaces in Isometric 464
Circles and Arcs in Isometric 464
Drawing Irregular Curves in Isometric 464
15-3 Common Features in Isometric 465
15-5 Common Features in Oblique 471
Circles and Arcs 471
Oblique Sectioning 472 Treatment of Conventional Features 472
15-6 Parallel, or One-Point, Perspective 474
Types of Perspective Drawings 475
Parallel, or One-Point, Perspective 476
Basic Steps to Follow for Parallel Perspective Sketching (Fig 15-47) 477
15.7 Angular, or Two-Point, Perspective 480
16-1 Modern Engineering Tolerancing 510
Trang 7viii Contents
16-2 Geometric Tolerancing S17
Feature Control Frame 517
Placement of Feature Control Frame 517
Form Tolerances 518
Straightness 519
16-3 Flatness S22
Flatness of a Surface 522
Flatness per Unit Area 522
Two or More Flat Surfaces in One Plane 522
16-4 Straightness of a Feature of Size S23
Features of Size 523
Material Condition Symbols (Modifiers) 524
Applicability of RFS, MMC, and LMC 525
Straightness of a Feature of Size 527
16-S Datums and the Three-Plane Concept S29
Examples of Orientation Tolerancing 535
Control in Two Directions 536
16-7 Datum Features Subject to Size Variation S37
Parts with Cylindrical Datum Features 537
Internal Cylindrical Features 545
External Cylindrical Features 548
Targets Not in the Same Plane 563
Partial Surfaces as Datums 565
Dimensioning for Target Location 565
16-12 Circularity and Cylindricity S6S
16-14 Correlative Tolerances S74
Coplanarity 574 Concentricity 575 Coaxiality 577 Symmetry 578 Runout 578
16-1S Positional Tolerancing for Noncylindrical Features S80
Noncircular Features at MMC 580
16-16 Positional Tolerancing for Multiple Patterns
of Features S84
Composite Positional Tolerancing 587
16-17 Formulas for Positional Tolerancing S91
Floating Fasteners 591 Calculating Clearance 592 Fixed Fasteners 592 Unequal Tolerances and Hole Sizes 594 Coaxial Features 594
Perpendicularity Errors 595
16-18 Summary of Rules for Geometric Tolerancing S9S
When to Use Geometric Tolerancing 595 Basic Rules 595
Review and Assignments S98
17-1 Two-Axis Control Systems 629
Computer Numerical Control (CNC) 629 Dimensioning for Numerical Control 630 Dimensioning for a Two-Axis Coordinate System 631
17-2 Three-Axis Control Systems 633
Dimensioning and Tolerancing 633
Review and Assignments 636
-Welding Drawings 641 18-1 Designing for Welding 641
Welding Processes 641
18-2 Welding Symbols 643
The Design of Welded Joints 648
18-3 Fillet Welds 6SO
Fillet Weld Symbols 650 Size of Fillet Welds 653
Trang 818-4 Groove Welds 654
18-5
Use of Break in Arrow of Bevel and J-Groove Welding
Other Basic Welds 660
19-1 The Design Process 686
The Design Process 686
The Engineering Approach to Successful
Selecting the Spur Gear Drive 736
20-5 Rack and Pinion 738 20-6 Bevel Gears 739
Working Drawings of Bevel Gears 740
20-7 Worm and Worm Gears 740
20-8 Comparison of Chain, Gear, and Belt Drives 744
Belts 744
Chain Drives Compared with Gear Drives 744
Chain Drives Compared with Belt Drives 745
Trang 9Contents
Cams, Linkages, and Actuators 792
22-1 Cams, Linkages, and Actuators 792
Cam Nomenclature 793
Cam Followers 794
Cam Motions 794
Simplified Method for Laying Out Cam Motion 798
Cam Displacement Diagrams 798
23-2 The Packaging Industry 827
23-3 Radial Line Development of Flat Surfaces 828
23-4 Parallel Line Development of Cylindrical
Pipe Drawings 867 Kinds of Pipes 867 Pipe Joints and Fitting 868
Piping Drawings 871
24-2 Isometric Projection of Piping Drawings 87S 24-3 Supplementary Piping Information 877 Review and Assignments 880
-Structural Drafting 887 2S-1 Structural Drafting 887
The Building Process 877 Structural Steel-Plain Material 888 Structural Drawing Practices 893
2S-2 Beams 894
Assembly Clearances 895 Simple Square-Framed Beams 896
2S-3 Standard Connections 898
Bolted Connections 898
2S-4 Sectioning 90S
Bottom Views 905 Elimination of Top and Bottom Views 905 Right- and Left-Hand Details 906
2S-S Seated Beam Connections 907 2S-6 Dimensioning 909
Bills of Material 910 Calculations of Weights (Masses) 911
Review and Assignments 912
Jigs and Fixtures 919 26-1 Jig and Fixture Design 919
Jigs 919 Drill Jigs 921 Drill Bushings 921
26-2 Drill Jig Components 923
Jig Body 923 Cap Screws and Dowel Pins 923 Locating Devices 924
Clamping Devices 926
Trang 10Fixture Design Considerations 932
Sequence in Laying Out a Fixture 935
Review and Assignments 936
Electrical and Electronics Drawings 940
27-1 Electrical and Electronics Drawings 940
27-3 Wiring (Connection) Diagrams 945
Basic Rules for Laying Out a Wiring Diagram 947
27-4 Printed Circuit Boards 947
CAD for Printed Circuit Boards 949 Basic Rules for Laying Out a Printed Circuit 951
27-5 Block and Logic Diagrams 951
Block Diagrams 951 Logic Diagrams 952 Graphic Symbols 952
Review and Assignments 956
Glossary G-1 Appendix-Standard Parts and Technical Data A-1 Index 1-1
xi
Trang 11Preface
Engineering Drawing and Design, Seventh Edition, prepares
students for drafting careers in modem, technology-intensive
industries Technical drafting, like all technical areas, is
constantly changing; the computer has revolutionized the
way in which drawings and parts are made This new edition
translates the most current technical information available
into the most useful for both instructor and student The book
covers graphic communication, CAD, functional drafting,
material representation, shop processes, geometric
toleranc-ing, true positiontoleranc-ing, numerical control, electronic drafttoleranc-ing,
and metrication The authors synthesize, simplify, and
con-vert complex drafting standards and procedures into
under-standable instructional units
Like previous editions, this one is at the cutting edge of
drafting and computer technologies Because board-drafting
skills are rapidly being replaced by computer-aided drafting
(CAD), this edition provides an enhanced view of CAD
while adhering to current ASME, ANSI, CSA, and ISO
stan-dards Drafters must be knowledgeable about CAD and about
international standards, for design files can now be
electron-ically transmitted across borders, or around the world
The reader will find that this book helps build basic
skills It also supplies the technical knowledge required in
today's marketplace
TEXT FEATURES
• Knowing and Applying Drawing Standards A
draw-ing made in the United States must meet the requirements
set out in various ASME drawing standards publications
Also, if a firm is involved in international marketing and
manufacturing, ISO guidelines (or other standards, such
as Canadian drawing standards) must be strictly
fol-lowed Drafters will be pleased to see that this book not
only covers these standards but also shows how to
inter-pret and apply them For example, the coverage of
geo-metric tolerancing and true position is more
comprehen-sive than in any other drafting text on the market
today
• Knowing Manufacturing Materials and Their
Processes The authors bring together and explain the
manufacturing materials that are available for
engineer-ing design They describe the manufacturengineer-ing processes
that influence the shape, appearance, and design of the
product
xii
• Knowing Fastening Methods The correct fastening
device plays a very important role in the cost, design, and appearance of a product Readers can learn about various types of fasteners, both permanent and remov-able, that are currently available
• Providing All the Necessary Information to Complete the Design The numerous assignments help the reader
gain practice These assignments can be completed with the help of a variety of Appendix tables reflecting real-world applications
• Unit Approach in Teaching the Subject Matter The
text's unit approach makes it possible for instructors to put together a customized program of instruction that suits the needs of their students and local industry
KEY FEATURES OF THE SEVENTH EDITION
Many users of the text were consulted before this new tion was undertaken In response to their suggestions and recommendations, we have made major changes and added new features to this Seventh Edition, including:
edi-• The four-color format is easy to read Color has been used as well to strengthen the important features in the
3000 line drawings and photographs
• Chapter 2 explains how drawings are produced by puters and peripherals Computers and the Internet Web have become not only a laboratory but also a limit- less technical resource and design facility
com-• Solid modeling continues to play an important role in Chap 15 The power of personal computers and work-stations brings 3-D modeling into the classroom, home, CAD office, and on-site manufacturing centers
• Chapter 16 contains more information on geometric tolerancing and guidance on how to apply it to various drawings The chapter is up to date with ASME standards and is more understandable to beginning students
• Chapter 19 covers concurrent engineering and project modeling Today, engineers and technicians work side
by side All team members are responsible for ing efforts to deliver on-time and on-budget finished products
Trang 12coordinat-• The section on stamping in Chap 23 it covers the
pro-cess of forming and cutting thicker-gage metals that are
used in manufacturing
• Chapter 27, on electronic drafting, is consistent with
solid-state, printed circuit board technology
• Many chapters include new CAD features They give
students and instructors a clear picture of how CAD can
be used in the classroom while maintaining a focus on
basic drafting principles Many CAD features include
assignments
• We have continued to provide the unit approach to
teaching, which divides chapters into "mini" teaching
units Instructors find this approach to be a real bonus
By choosing the appropriate units, instructors can put
together a customized program that suits the needs of
their students and local industry
• Design concepts are covered in the text through
draw-ing practice Graduates find that these concepts give
them an excellent background in drafting and design
Instructors can choose the units appropriate for their
program
• This text continues to provide the latest drawing
stan-dards, indispensable to instructors Current ANSI/ ASME
and ISO drawing practices are examined better here than
in any other text
• Numerous Internet assignments appear throughout the
book The Websites, which relate directly to the topic
of the unit, are of companies students might select to
survey possible career opportunities Instructors can
ask students to describe what they found at the sites
or to discuss sites that have the greatest regional career
interest Students can also view various technical
product lines
Each chapter begins with objectives and ends with
a chapter summary and list of key terms (both referenced
to chapter units) and draftinvg assignments A Glossary,
precedes the Appendix The four-color design highlights the text's special features Color is used to enhance the instruc-tional value of the material Thus, technical material is appealing visually and easy to follow and understand
Sev-Additional Chapters on Advanced Topics
Three additional chapters, covering advanced topics, are vided on the book's website:
pro-Chapter 28-Applied Mechanics Chapter 29-Strength of Materials Chapter 30-Fluid Power
Comments and suggestions concerning this and future editions of the text are most welcome
Visit the text website at: www.mhhe.com/jensen for various resources available to instructors and students
Trang 13Acknowledgments
The authors are indebted to the members of ASME
Y14.5M-1994 (R2004), Dimensioning and Tolerancing, and
the members of the CAN/CSA-B78.2-M91, Dimensioning
and Tolerancing of Technical Drawings, for the countless
hours they have contributed to making successful standards
The authors and staff of McGraw-Hill wish to express
their appreciation to the following individuals for their
responses to questionnaires and their professional reviews of
the new edition:
Trang 14About the Authors
Cecil H Jensen
Cecil H Jensen authored or coauthored many successful
technical books, including Engineering Drawing and
Design, Fundamentals of Engineering Drawing,
Funda-mentaL~ of Engineering Graphics (formerly called
Draft-ing Fundamentals), InterpretDraft-ing EngineerDraft-ing DrawDraft-ings,
Geometric Dimensioning and Tolerancing for Engineering
and Manufacturing Technology, Architectural Drawing
and Design for Residential Construction, Home Planning
and Design, and Interior Design Some of these books
Jay D Helsel
Jay D Helsel is professor emeritus of applied engineering
and technology at California University of Pennsylvania He
earned the master's degree from Pennsylvania State University
and a doctoral degree in educational communications and
technology from the University of Pittsburgh He holds a
certificate in airbrush techniques and technical illustration
from the Pittsburgh Art Institute He has worked in industry
and has also taught drafting, metalworking, woodworking,
Dennis R Short
Dennis R Short is professor of computer graphics
tech-nology at the School of Techtech-nology, Purdue University He
completed his undergraduate and graduate work at Purdue
University and also studied at the University of Maryland,
College Park He enjoys teaching traditional engineering
design and drafting, computer-aided drafting and design,
computer-integrated manufacturing (CIM), and advanced
modeling and animation While at Purdue, he implemented
were printed in three languages and are popular in many countries
Mr Jensen was a member of the Canadian Standards Committee (CSA) on Technical Drawings (which includes both mechanical and architectural drawing) and headed the Committee on Dimensioning and Tolerancing He was Canada's ANSI representative He represented Canada at two world ISO conferences in Oslo and Paris on the standardization of techni-cal drawings Cecil Jensen passed away in April, 2005
and a variety of laboratory and professional courses at both the secondary and the college levels
Dr Helsel is now a full-time writer He coauthored
Engineering Drawing and Design, Fundamentals of neering Drawing, Programmed Blueprint Reading, the popular high school drafting textbook Mechanical Drawing: Board and CAD Techniques, now in its thirteenth edition, and Interpreting Engineering Drawings
Engi-the first instructional CAD system for Engi-the School of ogy, as well as the first networked PC-based CAD labora-tory In addition to teaching undergraduates, he is on the graduate faculty He codirects the Purdue International Cen-ter for Entertainment Technology (PICET), a university-level interdisciplinary research and development center Dr Short
Technol-prepared the Instructor Wraparound Edition for Engineering Drawing and Design, Fifth and Sixth Editions
XV
Trang 17Chapter 1
Engineering Graphics
as a Language
OBJECTIVES
After studying this chapter, you will be able to:
• Define common terms used in drawing and design ( 1-1)
• Describe drawing standards and the standards organizations (1-1)
• Understand the training and qualifications needed for careers in drawing and design (1-2)
• Understand the uses of CAD in the drafting office (1-3)
• Describe drafting equipment such as drafting machines, slides, triangles, scales, and compasses (1-4)
• Use pencils and erasers in drafting (1-4)
Since earliest times people have used drawings to communicate and record ideas
so that they would not be forgotten Graphic representation means dealing
with the expression of ideas by lines or marks impressed on a surface A drawing
is a graphic representation of a real thing Drafting, therefore, is a graphic
language, because it uses pictures to communicate thoughts and ideas Because these pictures are understood by people of different nations, drafting is referred
to as a universal language
Drawing has developed along two distinct lines, with each form having a
different purpose On the one hand artistic drawing is concerned mainly with the expression of real or imagined ideas of a cultural nature Technical drawing,
on the other hand, is concerned with the expression of technical ideas or ideas
of a practical nature, and it is the communication method used in all branches
of technical industry
Even highly developed word languages are inadequate for describing the size, shape, texture and relationship of physical objects For every manufactured object there are drawings that describe its physical shape and size completely and accurately, communicating engineering concepts to manufacturing For this
reason, drafting is called the language of industry
Drafters translate the ideas, rough sketches, specifications, and calculations
of engineers, architects, and designers into working plans that are used in making
a product (Table 1-1) Drafters calculate the strength, reliability, and cost of materials In their drawings and specifications, they describe exactly what mate-rials workers are to use on a particular job To prepare their drawings, drafters
Trang 18TABLE 1-1 Various fields of drafting
Planning Designing Supervising
Designing Developing Supervising Programming
Planning Designing Testing
Designing Testing Manufacturing Maintenance Construction
Planning Designing Manufacturing Construction
Promotion Designing Illustrating
Materials Machines Devices
Buildings Environment Landscape
Computers Electronics Power Electrical
Missiles Planes Satellites Rockets
Buildings Hydraulics Pneumatics Pipe lines
Catalogs Magazines Displays
Power generation Transportation Manufacturing Power services Atomic energy Marine vessels
Commercial buildings Residential buildings Institutional buildings Environmental space forms
Power generation Power application Transportation Illumination Industrial electronics Communications Instrumentation Military electronics Aerodynamics Structural design Instrumentation Propulsion systems Materials
Reliability testing Production methods
Liquid transportation Manufacturing Power services Hydraulics Pneumatics
Structural designs :Buildings Planes Ships Automobiles Bridges New products Assembly instructions Presentations community projects Renewal programs
3
Trang 194 PART 1 Basic Drawing and Design
use either computer-aided drawing and design (CAD)
sys-tems or board drafting instruments, such as compasses,
pro-tractors, templates, and triangles, as well as drafting machines
that combine the functions of several devices They also may
use engineering handbooks, tables, and calculators to assist
in solving technical problems
Drafters are often classified according to their type of
work or their level of responsibility Senior drafters (designers)
use the preliminary information provided by engineers and
architects to prepare design layouts (drawings made to scale
of the object to be built) Detailers Gunior drafters) make
drawings of each part shown on the layout, giving
dimen-sions, material, and any other information necessary to make
the detailed drawing clear and complete Checkers carefully
examine drawings for errors in computing or recording sizes
and specifications
Drafters may also specialize in a particular area, such as
mechanical, electrical, electronic, aeronautic, structural,
pip-ing, or architectural drafting
Drawing Standards
Throughout the long history of drafting, many drawing
con-ventions, terms, abbreviations, and practices have come into
common use It is essential that different drafters use the
same practices if drafting is to serve as a reliable means of
communicating technical theories and ideas
In the interest of worldwide communication, the
Inter-national Organization of Standardization (ISO) was
estab-lished in 1946 One of its committees, ISO TCIO, was
formed to deal with the subject of technical drawings Its
goal was to develop a universally accepted set of drawing
standards Today most countries have adopted, either in full
or with minor changes, the standards established by this
committee, making drafting a truly universal language
The American Society of Mechanical Engineers (ASME)
is the governing body that establishes the standards for the
United States through its ASME Y14.5 committee (ANSI),
made up of selected personnel from industry, technical
orga-nizations, and education Members from the ASME Yl4.5
also serve on the ISO TCIO subcommittee
The standards used throughout this text reflect the current
thinking of the ASME standards committee These standards
apply primarily to end-product drawings End-product
draw-ings usually consist of detail or part drawings and assembly
or subassembly drawings, and are not intended to fully cover
other supplementary drawings, such as checklists, item lists,
schematic diagrams, electrical wiring diagrams, flowcharts,
installation drawings, process drawings, architectural
draw-ings, and pictorial drawings
The information and illustrations presented here have
been revised to reflect current industrial practices in the
preparation and handling of engineering documents The
increased use of reduced-size copies of engineering
draw-ings made from microfilm and the reading of microfilm
require the proper preparation of the original engineering
document regardless of whether the drawing was made
manually or by computer (CAD) All future drawings
should be prepared for eventual photographic reduction or reproduction The observance of the drafting practices described in this text will contribute substantially to the improved quality of photographically reproduced engineering drawings
careers in drafting and related technical fields:
www.bls.gov/bls/occupation
1-2 CAREERS IN ENGINEERING GRAPHICS
The Student
While students are learning basic drafting skills, they will also
be increasing their general technical knowledge, learning about some of the enginering and manufacturing processes involved in production Not all students will choose a drafting career However, an understanding of this graphic language is necessary for anyone who works in any of the fields of tech-nology, and is essential for those who plan to enter the skilled trades or become a technician, technologist, or engineer Because a drawing is a set of instructions that the worker will follow, it must be accurate, clean, correct, and complete When drawings are made with the use of instruments, they
are called instrument (or board) drawings When they are
developed with the use of a computer, they are known as
computer-aided drawings When made without instruments
or the aid of a computer, drawings are referred to as sketches
The ability to sketch ideas and designs and to produce rate drawings is a basic part of drafting skills
accu-In everyday life, a knowledge of technical drawings is helpful in understanding house plans and assembly, mainte-nance, and operating instructions for many manufactured or hobby products
Places of Employment
There are well over 300,000 people working in CAD or drafting positions in the United States A significant number
of them are women About 9 out of 10 drafters are employed
in private industry Manufacturing industries that employ a large number of drafters are those making machinery, electri-cal equipment, transportation equipment, and fabricated metal products Nonmanufacturing industries employing a large number of drafters are engineering and architectural consulting firms, construction companies, and public utilities
Drafters also work for the government; the majority work for the armed services Drafters employed by state and local governments work chiefly for highway and public works
Trang 20departments Several thousand drafters are employed by
colleges and universities and by other nonprofit organizations
Training, Qualifications, and Advancement
Many design careers are available at different technical levels
of performance Most companies are in need of design and
drafting services for growth in technical development,
con-struction, or production Any person interested in becoming
a drafter can acquire the necessary training from a number
of sources, including junior and community colleges,
exten-sion diviexten-sions of universities, vocational/technical schools,
and correspondence schools Others may qualify for drafting
positions through on-the-job training programs combined
with part-time schooling
The prospective drafter's training in post-high school
drafting programs should include courses in mathematics
and physical sciences, as well as in CAD and CADD Studying
fabrication practices and learning some trade skills are
also helpful, since many higher-level drafting jobs require
knowledge of manufacturing or construction methods This
is especially true in the mechanical discipline because of the
implementation of CAD/CAM (computer-aided drawing/
computer-aided manufacturing) Many technical schools
offer courses in structural design, strength of materials,
physical metallurgy, CAM, and robotics
As drafters gain skill and experience, they may advance
to higher-level positions such as checkers, senior drafters,
designers, supervisors, and managers (Fig 1-1) Drafters who
take additional courses in engineering and mathematics are
often able to qualify for engineering positions
Qualifications for success as a drafter include the ability
to visualize objects in three dimensions and the development
of problem-solving design techniques Since the drafter is the
one who finalizes the details on drawings, attentiveness to
detail is a valuable asset
Employment Outlook
Employment opportunities for drafters are expected to remain
stable as a result of the complex design problems of modern
Fig 1-1 Positions within the drafting office
CHAPTER 1 Engineering Graphics as a Language 5
products and processes The need for drafters will, however, fluctuate with local and national economics Since drafting
is a part of manufacturing, job opportunities in this field will also rise or drop in accordance with various manufacturing industries The demand for drafters will be high in some areas and low in others as a result of high-tech expansion or
a slump in sales In addition, computerization is creating many new products, and support and design occupations, including drafters, will continue to grow On the other hand, photo-reproduction of drawings and expanding use of CAD have eliminated many routine tasks done by drafters This development will probably reduce the need for some less skilled drafters
References and Source Materials
1 Charles Bruning Co
2 Occupational Outlook Handbook
on drafting certification, specific job openings, and
opportunities to post resumes: http://www.adda.org/
1-3 THE DRAFTING OFFICE
Drafting room technology has progressed at the same rapid pace as the economy of the country Many changes have taken place in the modern drafting room compared to the typical drafting room scene before CAD, as shown in Fig 1-2,
p 6 Not only is there far more equipment, but it is of much higher quality Noteworthy progress has been and continues
to be made
The drafting office is the starting point for all engineering work Its product, the engineering drawing, is the main method of communication among all people concerned with the design and manufacture of parts Therefore, the drafting office must provide accommodations and equipment for the drafters, from designer and checker to detailer or tracer; for the personnel who make copies of the drawings and file the originals; and for the secretarial staff who assist in the prep-aration of the drawings Typical drafting workstations are shown in Figs 1-3 and 1-4, p 6
Fewer engineering departments now rely on board ing methods Computers are replacing drafting boards at a steady pace because of increased productivity However, where a high volume of finished or repetitive work is not necessary, board drafting does the job adequately CAD and board drafting can serve as full partners in the design process, enabling the designer to do jobs that are simply not possible
draft-or feasible with board equipment alone
Besides increasing the speed with which a job is done,
a CAD system can perform many of the tedious and repetitive
Trang 216 PART 1 Basic Drawing and Design
(A) THE DRAFTING OFFICE AT THE TURN OF THE CENTURY
(B) BOARD DRAFTING OFFICE UP TO 1970
(C) TODAY'S DRAFTING OFFICE
Fig 1-2 Evolution of the drafting office
tasks ordinarily required of a drafter, such as lettering and
differentiating line weights CAD thus frees the drafter to be
more creative while it quickly performs the mundane tasks
of drafting It is estimated that CAD has been responsible
Fig 1-3 Board drafting office
Fig 1-4 CAD drafting office
for an improvement of at least 30 percent in production in terms of time spent on drawing
A CAD system by itself cannot create A drafter must create the drawing, and thus a strong design and drafting background remains essential
It may not be practical to handle all the workload in a design or drafting office on a CAD system Although most design and drafting work certainly can benefit from it, some functions will continue to be done by traditional means Thus some companies use CAD for only a portion of the workload Others use CAD almost exclusively Whatever the percentage of CAD use, one fact is certain: It has had, and will continue to have, a dramatic effect on design and drafting careers
Once a CAD system has been installed, the required personnel must be hired or trained Trained personnel gener-ally originate from one of three popular sources: educational institutions, CAD equipment manufacturer training courses, and individual company programs
Trang 22INTERNET CONNECTION Visit the following site for
information on computers and related accessories for
the drafting office: http://www.ibm.com/
Examine this site and report on the typical furniture
and equipment needed when planning a new drafting
office: http://www.mayline.com/
Obtain information on the latest printers, scanners, and
copiers: http://www.hewlett-packard.com/
1-4 BOARD DRAFTING
Over the years, the designer's chair and drafting table have
evolved into a drafting station that provides a comfortable,
integrated work area Yet much of the equipment and
sup-plies employed years ago are still in use today, although
vastly improved
Drafting Furniture
Special tables and desks are manufactured for use in
single-station or multisingle-station design offices Typical are desks with
attached drafting boards The boards may be used by the
occupant of the desk to which it is attached, in which case
it may swing out of the way when not in use, or may be
reversed for use by the person in the adjoining station
In addition to such special workstations, a variety of
individual desks, chairs, tracing tables, filing cabinets, and
special storage devices for equipment are available
The drawing sheet is attached directly to the surface of
a drafting table (Fig 1-5) Most professional drafting tables
WOOD DRAFTING TABLE STEEL DRAFTING TABLE
ELECTRIC DRAFTING TABLE
Fig 1-5 Drafting tables
CHAPTER 1 Engineering Graphics as a Language 7
Fig 1-6 Board drafting equipment
have a special overlay drawing surface material that "recovers" from minor pinholes and dents
Drafting Equipment
See Fig 1-6 for a variety of drafting equipment
Drafting Machines
In a manually equipped drafting office, where the designer
is expected to do accurate drafting, a drafting machine,
or parallel slide, is used A drafting machine, which is attached to the top of the table, combines the functions of
a parallel slide, triangles, scale, and protractor and is estimated to save up to 50 percent of the user's time All positioning is done with one hand, and the other hand is free to draw
Two types are currently available (Fig 1-7, p 8) In the track type, a vertical beam carrying the drafting instruments rides along a horizontal beam fastened to the top of the table
In the arm (or elbow) type, two arms pivot from the top of the machine and are relative to each other
The track-type machine has several advantages over the arm type It is better suited for large drawings and is nor-mally more stable and accurate The track type also allows the drafting table to be positioned at a steeper angle and per-mits locking in the vertical and horizontal positions Some track-type drafting machines provide a digital dis-play of angles, the X- Y coordinates, and a memory function
Parallel Slide
The parallel slide, also called the parallel bar, is used in
drawing horizontal lines and for supporting triangles when vertical and sloping lines are being drawn (Fig 1-8, p 8)
It is fastened on each end to cords, which pass over leys This arrangement permits movement up and down the
Trang 23pul-8 PART 1 Basic Drawing and Design
(A) TRACK TYPE
(B)ARMTVPE Fig 1-7 Drafting machines
board while maintaining the parallel slide in a horizontal
position
Triangles
Triangles are used together with the parallel slide when
you are drawing vertical and sloping lines (Fig 1-9) The
triangles most commonly used are the 30/60° and the
Fig 1-8 Drafting table with parallel slide
45° triangles Singly or in combination, these triangles can
be used to form angles in multiples of 15° For other angles, the adjustable triangle (Fig 1-11) is used (p 10)
Scales
Scale may refer to the measuring instrument or the size to
which a drawing is to be made
Measuring Instrument Shown in Fig 1-10, p 10, are the common shapes of scales used by drafters to make measure-ments on their drawings Scales are used only for measuring and are not to be used as a straightedge for drawing lines It
is important that drafters draw accurately to scale The scale
to which the drawing is made must be given in the title
block or strip that is part of the drawing
Sizes to Which Drawings Are Made When an object is
drawn at its actual size, the drawing is called full scale
or scale 1:1 Many objects, however, such as buildings,
ships, or airplanes, are too large to be drawn full scale,
so they must be drawn to a reduced scale An example would be the drawing of a house to a scale of 1,4 in = 1 ft
or 1:48
Frequently, objects such as small wristwatch parts are drawn larger than their actual size so that their shape can be seen clearly and dimensioned Such a drawing has been drawn to an enlarged scale The minute hand of a wristwatch, for example, could be drawn to a scale of 5:1
Many mechanical parts are drawn to half scale, 1:2, and quarter scale, 1:4, or nearest metric scale, 1:5 The scale to which the part is drawn and the actual size of the part are shown as an equation, the drawing scale shown first With reference to the 1:5 scale, the left side of the equa-tion represents a unit of the size drawn; the right side repre-sents the equivalent 5 units of measurement of the actual object
Scales are made with a variety of combined scales marked on their surfaces This combination of scales spares the drafter the necessity of calculating the sizes to be drawn when working to a scale other than full size
Trang 24Fig 1-9 Triangles
Metric Scales The linear unit of measurement for
mechan-ical drawings is the millimeter Scale multipliers and divisors
of 2 and 5 are recommended (Fig 1-12, p 10)
The units of measurement for architectural drawings are
the meter and millimeter The same scale multipliers and
divisors used for mechanical drawings are used for
architec-tural drawings
Inch (U.S Customary) Scales
Inch Scales There are three types of scales that show
var-ious values that are equal to 1 inch (in.) (Fig 1-13, p 11 )
They are the decimal inch scale, the fractional inch scale,
and the scale that has divisions of 10, 20, 30, 40, 50, 60,
and 80 parts to the inch The last scale is known as the civil
engineer's scale It is used for making maps and charts
(A) THE 45° TRIANGLE
(B) THE 60° TRIANGLE
(C) THE TRIANGLES IN COMBINATION
The divisions, or parts of an inch, can be used to represent feet, yards, rods, or miles This scale is also useful in mechanical drawing when the drafter is dealing with deci-mal dimensions
On fractional inch scales, multipliers or divisors of 2, 4,
8, and 16 are used, offering such scales as full size, half size, and quarter size
Foot Scales These scales are used mostly in architectural work (Fig 1-14, p 11) They differ from the inch scales in that each major division represents a foot, not an inch, and end units are subdivided into inches or parts of an inch The more common scales are Ys in = 1 ft, Y in = 1 ft, 1 in =
1 ft, and 3 in = 1 ft The most commonly used inch and foot scales are shown in Table 1-2, p 12
Trang 2510 PART 1 Basic Drawing and Design
REGULAR RELIEVED FACET
DOUBLE
BEVEL
OPPOSITE BEVEL
FLAT BEVEL
Fig 1-10 Drafting scales
Fig 1-11 Adjustable triangle
• Friction head compass, standard in most drafting sets
• Bow compass, which operates on the jackscrew or ratchet
principle by turning a large knurled nut
• Drop bow compass, used mostly for drawing small cles The center rod contains the needle point and remains stationary while the pencil leg revolves around it
cir-• Beam compass, a bar with an adjustable needle and and-pen attachment for drawing large arcs or circles
Trang 26pencil-DECIMAL INCH SCALE (FULL SIZE)
DECIMAL INCH SCALE (HALF SIZE)
CIVIL ENGINEER SCALE (30 DIVISIONS)
Fig 1·13 Inch scales
I " = I' -0" SCALE
1/4" =I'-0" SCALE
Fig 1-14 Recommended foot and inch drawing scales
• Adjustable arc, also called a curved ruler, is a device
used to accurately draw any radius from 7 to 20 in (200
to 5000 mm)
The bow compass is adjusted by turning a screw whose knurled head is located either in the center or to one side The bow compass can be used and adjusted with one hand
as shown in Fig 1-16, p 12 The proper technique is:
1 Adjust the compass to the correct radius
2 Hold the compass between the thumb and finger
3 With greater pressure on the leg with the needle located
on the intersection of the center lines, rotate the compass
in a clockwise direction The compass should be slightly tipped in the direction of motion
Pencils
As with all other equipment, advances in pencil design have made drawing lines and lettering easier The new auto-matic pencils are designed to hold leads of one width, thus eliminating the need to sharpen the lead These pencils
Trang 27TABLE 1-2 Recommended drawing scales
1:2 1:4 1:8 1:12 1:16 1:24 I:32 1:48 1:64 1:96 1:192
Trang 28(color-AUTOMATIC
MECHANICAL
Fig 1.17 Drafting pencils
selected line width, lead hardness, and make, for performing
particular line or lettering tasks on film or paper
Another type of drafting pencil, often referred to as a
mechanical pencil or lead holder, advances a uniformly sized
lead that periodically requires sharpening The leads for the
mechanical pencils are usually sharpened in a mechanical
lead pointer, which produces a tapered point A sandpaper
block is used to sharpen compass leads
Erasers and Cleaners
Erasers A variety of erasers have been designed to do
spe-cial jobs-remove surface dirt, minimize surface damage on
film or vellum, and remove ink or pencil lines
Cleaners An easy way to clean tracings is to sprinkle them
lightly with gum eraser particles while working Then
tri-angles, scales, etc., stay spotless and clean the surface
auto-matically as they are moved back and forth The particles
contain no grit or abrasive, and will actually improve the
lead-taking quality of the drafting surface
Erasing Shields Erasing shields are thin pieces of metal
or plastic (Fig 1-18) that have a variety of openings to
per-mit the erasure of fine detail lines or lettering without
dis-turbing nearby work that is to be left on the drawing With
this device, erasures can be made quickly and accurately
Fig 1-18 Erasing shield
CHAPTER 1 Engineering Graphics as a Language 13
Brushes
A soft brush is used to keep the drawing area clean By using
a brush to remove eraser particles and any accumulated dirt, the drafter avoids smudging the drawing
Templates
To save time, drafters use templates (Fig 1-19) for drawing
circles and arcs Templates are available with standard hole sizes ranging from small to 6.00 in (150 mm) in diameter Templates are also used for drawing standard square, hex-agonal, triangular, and elliptical shapes and standard electrical and architectural symbols
Irregular Curves
For drawing curved Jines in which, unlike the case with cular arcs, the radius of curvature is not constant, a tool
cir-known as an irregular or French curve (Fig 1-20) is used
The patterns for these curves are based on various tions of ellipses, spirals, and other mathematical curves The curves are available in a variety of shapes and sizes Normally, the drafter plots a series of points of intersection along the
Trang 2914 PART 1 Basic Drawing & Design
Fig 1-20 Irregular curves
desired path and then uses the French curve to join these
points so that a smooth-flowing curve results
Curved Rules and Splines
Curved rules and splines (Fig 1-21) solve the problem of
ruling a smooth curve through a given set of points They lie
flat on the board and are as easy to use as a triangle; yet they
can be bent to fit any contour to a 3-in (75-mm) minimum
radius and will hold the position without support
See Assignments 1 through 4 for Unit 1-4, on pages 16 and 17
drafting and CAD media: http://nationwidedrafting.com
Select and compare various drafting instruments and
inking supplies for drafting and fine arts:
Trang 30SUMMARY
1 Drafting is a universal language because it uses pictures
to communicate; everyone can understand graphic
rep-resentations Drafting is regarded as the language of
industry because it can accurately convey engineering
concepts to manufacturers (1-1)
2 Organizations such as the International Organization of
Standardization (ISO) and the American Society of
Mechanical Engineers (ASME) have established
draw-ing standards that are followed by the industry ASME
Y14.5 standards are followed in this text (1-1)
3 Manual or instrument drawings are made with the use
of instruments; drawings made with the use of a
com-puter are called comcom-puter-aided drawings (1-1)
4 Career opportunities in drafting occur in both
manufac-turing and nonmanufacmanufac-turing industries The types of
positions range from those involved in manufacturing
machinery and electrical equipment to positions in
archi-tecture firms and public utilities (1-2)
5 The product of the drafting office is the engineering
drawing Nowadays computers (CAD-computer-aided
drawing) have essentially replaced the drafting board,
bringing about increases in speed and reductions in cost
However, board drafting still has its place (1-3)
KEY TERMS
6 In manually equipped offices, track-type or arm (elbow) drafting machines are generally used The drafter using these machines also needs to be familiar with the use of the parallel slide and the triangle (1-4)
7 The word scale applies to both a measuring instrument
and the size to which a drawing is made Drawings must indicate the scale to which a drawing has been done A full-scale drawing has a scale of 1:1 However, most of the time, a drawing must be made to a reduced scale; for example, a scale might be lfil in = 1 ft or 1:48 (1-4)
8 When a metric scale is used in mechanical drawings, the linear unit of measure is the millimeter (mm) With the inch (U.S customary) units, three types of scales are used: the decimal inch scale, the fractional inch scale, and the civil engineer's scale The foot scale is used in architectural work ( 1-4)
9 Several basic types of compasses are used in ing (1-4)
draft-10 Among the tools the board drafter must be proficient in using are different types of pencils, erasers and cleaners, and brushes (1-4)
11 Drafters use templates, the irregular (or French) curve, and curved rules and splines (4-1)
Artistic drawing (1-1)
CAD (1-1)
Engineering drawing (1-1) Erasing shield ( 1-4)
Sketches (1-1) Standards (1-1) Technical drawing (1-1) Templates ( 1-4)
Layouts (1-1) Parallel slide or bar ( 1-4) Protractor (1-4)
Scale (1-4)
Title block (1-4) Triangles ( 1-4)
15
Trang 3116 PART 1 Basic Drawing & Design
ASSIGNMENTS
1 Using the scales shown in Fig 1-22 below, determine
lengths A through K
2 Metric measurements assignment With reference to
Fig 1-23 on the next page, use the scale listed at
FRACTIONAL INCH SCALE - !FULL SCALE)
I"= I'-0" SCALE- (1:12 SCALE)
Fig 1-22 Reading drafting scales
1: 1 measure distances A through E 1:2 measure distances F through K 1:5 measure distances L through P
1: 10 measure distances Q through U 1:50 measure distances V through Z
Trang 323 Inch measurement assignment With reference to Fig 1-23
and using the scale:
1: 1 decimal inch scale; measure distances A through F
1: 1 fractional inch scale; measure distances G through M
1:2 decimal inch scale; measure distances N through T
1:2 fractional inch scale; measure distances U through Z
4 Foot and inch measurement assignment With reference
to Fig 1-23 and using the scale:
Trang 33Chapter 2
Computer-Aided
Drawing (CAD)
OBJECTIVES
After studying this chapter, you will be able to:
• Discuss how CAD developed and describe the industries that led its development (2-1)
• Understand the role of CAD in an integrated engineering and design environment (2-1)
• List the principal components of a CAD system-both hardware and software (2-2)
• Discuss the broader environment in which CAD systems operate-LANs, WANs, and the World Wide Web (WWW) (2-3)
• Describe how a network functions and explain the advantages of using a network in a CAD environment (2-3)
• Define terms such as CAD/CAM, CNC, and CIM (2-4)
The term computer-aided design (CAD) refers to a family of computer-based
technologies that are used to create, analyze, and optimize engineering designs
Typical CAD programs provide a graphical user interface (GUI) that allows
the user to create and manipulate of 2-D and 3-D geometry, produce ing drawings, conduct basic engineering analysis such as mass properties cal-culations, and to visualize individual parts and complex assemblies (Fig 2-1) The development of CAD systems has paralleled the development of computer technology over the past 40 years and reflects the increasing power and decreas-ing cost of computer systems
engineer-The development of industrial CAD systems began in the 1960s, when panies in the automotive and aerospace industries started to use large mainframe computer systems Development continued in the 1970s with the introduction of
com-interactive computer graphics terminals, programs that evolved from simple 2-D
drafting programs to more complex 3-D geometry systems (Fig 2-2) This decade also saw the emergence of the first computer-aided manufacturing (CAM) soft-ware In the 1980s, with the introduction of more powerful personal computers based on Intel processors, small and medium-size companies were able to afford and use the new CAD systems In the 1990s, more advanced 3-D CAD packages
using solid modeling and NURBS (non-uniform rational B-splines) surfaces were
developed The integration of CAD into engineering and manufacturing advanced
Trang 34Fig 2-1 AutoCAD screen
Fig 2-2 CAD system equipment
due to the development of high-speed networking and the
Internet The new millennium saw the advent of advanced
visualization systems such as Virtual Reality as well as more
powerful systems that had better display systems and greatly
increased storage capacity
As CAD developed, so did computer-aided
manufac-turing (CAM) and computer-aided engineering (CAE)
The acronym CAD is often seen paired with CAM (as
in CAD/CAM) to reflect the close ties between drafting
and manufacturing In the 1990s, reflecting advances in
network and communication technologies,
computer-integrated manufacturing (CIM), and concurrent
engi-neering also came into use
For members of an engineering design team, the ability
to work cooperatively in an organized and structured environment
CHAPTER 2 Computer-Aided Drawing (CAD) 19
is very important Groups involved in engineering design or manufacturing may be working in different departments, plants, countries, or even continents CAD software permits the rapid exchange of design and manufacturing information regardless of where the team members may be located This global view and the teamwork it requires are key characteristics of manufacturing and design in the twenty-first century
See questions 1 through 3 for Unit 2-1 on page 30
INTERNET CONNECTION Report on CAD software for all aspects of drafting and design:
http:/ /www.autodesk.com/
List current information on CAD equipment and accessories, including computers, servers, storage devices, and printers: http://www.ibm.com/, http:/ /www.dell.com, http:/ /www.hp.com Visit the following site for information on CAD, CAM, and CIM software: http://www.solidworks.com/
Describe available software from CATIA and PTC: http:/ /www.catia.ibm.com, http:/ /www.ptc.com Search the web for additional resources
2-2 COMPONENTS OF A CAD SYSTEM
CAD systems consist of two major components: hardware and software Hardware is made up of the physical components of the systems including the computer system, graphics display, input devices (mouse or tablet), output devices (printers and plotters), and other specialized equipment such as 3-D digitiz-ers Software consists of the CAD program itself, related sup-port programs or utilities, and an operating system, usually Windows XP, Windows VISTA or UNIX or LINUX
Hardware
The typical hardware components of a CAD system consist
of a workstation and one or more graphics displays, along with associated input and output devices A workstation con-tains one or more processors that perform the numerical cal-culations, RAM (random access memory) used to tempo-rarily store the program and data, and one or more hard drives used to permanently store programs and data CAD workstations are capable of connecting to a network of com-puters through a network interface A high-resolution graph-ics display, 512MB (megabyte) or more of Video Memory,
is required to display the CAD data An input device, usually
a three-button or two-button wheel mouse, is required to select commands and position graphics on the screen
Trang 3520 PART 1 Basic Drawing and Design
Workstations
CAD workstations are usually either high-end PCs or, less
frequently, UNIX-based graphics workstations Fast,
power-ful processors (CPUs), large amounts of memory (RAM)
and disk storage, high-resolution display devices, and the
capability to being networked characterize workstations The
power and capabilities of these computers increased steadily
during the 1990s, and during that time, costs have decreased
The trend of increasing capability and decreasing cost of
computer systems had been predicted by Moore's law, which
is named after Intel's founder, Gordon Moore, and states that
device complexity, such as speed and capacity, should double
about every 18 months
State-of-the-art workstations usually will have one or
more dual-core processors, 2 GB (gigabyte) or more of
RAM (Fig 2-3), and 400 GB or more of hard drive storage
(Fig 2-4 ) Workstations also are characterized by a large
number of expansion slots and USB2 connections that allow
for the connection of other devices and components, such as
flash and portable drives
All systems should have a rewritable DVD-RW (Fig 2-5)
for installing software and archiving data These systems
also should be protected by in-line surge protectors that
Fig 2-3 Dual-core processor
Fig 2-4 Hard-drive storage of 40 GB
Fig 2-5 DVD R/W unit
Trang 36Fig 2-6 UPS (uninterruptible power supply) unit suitable for a
server or workstation
Fig 2-7 Real-time fingerprint verification using silicon sensors
prevent power spikes from damaging the system, and they also should be connected to an intelligent, uninterruptible power supply (Fig 2-6) that can provide power to a system when it shuts down without losing or corrupting data Many systems also have security systems that go beyond simple password selection Workstations containing sensitive or valuable data may use a biometric identification system that recognizes authorized users by fingerprint or retinal scan (Fig 2-7)
Storage and Display Devices
Current workstations now use LCD flat-panel displays (Fig 2-8)
as the older cathode-ray tube (CRT) displays largely have been replaced by the newer technology FPDs use liquid-crystal dis-play (LCD) technology and have the advantages of reduced radiation, lower power requirements that result in less heat, and also use less desk space
All displays are classified by the diagonal measurement of the display area and the resolution of the display expressed in
pixels, or picture elements, the smallest addressable area of a display Many CAD workstations have displays that are 1280 pixels wide by 1024 pixels high with higher resolutions avail-able Wide-screen displays or dual displays are becoming com-monplace on CAD workstations Users should avoid touching the display screen with pens or their fingers, as this can damage the screen LCD monitors only should be cleaned following the manufacturer's recommendations to avoid running the display Storage devices used in CAD workstations can be classi-fied into two main types: fixed and removable media Fixed
drives, commonly referred to as hard drives, can range have
400 GB, or more, in capacity Larger amounts of disk storage can be obtained by combining disks in special systems called
redundant arrays of independent disks (RAIDs) (See Fig 2-9,
p 22.) These drive systems can be configured to store
thou-sands of gigabytes (TB-terabytes) of data for large work
groups or complex projects
Fig 2-8 Typical LCD displays
Trang 3722 PART 1 Basic Drawing and Design
computer
Fig 2-9 Large-capacity RAID (redundant arrays of independent disks) s.tora~e syst~m In a
simplified RAID array, data is written to two or more disks at once, resultm~ m II_Iulbple
copies This protects data in case one disk fails In sophisti~ate~ RAID co~f1gur.at10ns, data
from a single file is spread over multiple disks Error checkmg 1s also provided m such arrays
Removable media drives can be as simple as the common
and now essential obsolete, 3.5-in diskette that stores
approx-imately 1 MB of data DVD-R/W drives are now on all new
systems, and these disks can store 4.7 GB for a single-layer,
single-sided disk, and 8.5 GB for a double-layer, single-sided
disk Flash drives (Fig 2-10), also know as thumb drives, are
convenient and can store 1 GB or more Portable USB hard
drives (Fig 2-11) also can be considered a form of removable
storage and easily can store over 100 GB
All removable media should be stored properly,
identi-fied, and labeled DVDs and CDs should be kept in jewel
cases to avoid damage such as scratches, and you should
handle CDs and DVDs only by the edges Labels rather than
pens or markers should be used Media should never be
exposed to extremes of temperature or humidity Media that
has been transported should be allowed to return to room
temperature before being used
Fig 2-10 Flash drives are a convenient type of removable
media drive
Input Devices
The basic input device for a CAD workstation is the board (Fig 2-12) This device is used for inputting alphanu-meric data and has programmable function keys that can be used to reduce the number of keystrokes required for com-mon command sequences All workstations in use today also have a mouse device with two or more buttons (Fig 2-13) The mouse is used to move the cursor about the display window and to select commands or geometry To avoid repetitive motion injuries, the mouse and keyboard should be positioned properly and the user should maintain correct pos-ture A mouse pad should always be used, and accumulated dust and debris should be cleaned from the internal rollers
key-or optical window of the mouse every so often
Specialized input devices can be used on some CAD workstations, among them tablets and mouse-type devices
Fig 2-11 A typical USB hard drive
Trang 38Fig 2-12 Ergometric keyboard reduces repetitive motion
injuries
Click Double-click Drag
Fig 2-13 Three common mouse techniques_
that can be controlled in three or more axes Tablets come
with pressure-sensitive pens and can be used for sketching
and other more artistic activities, such as concept sketches
and drawings Multi-axis devices can be used to manipulate
(A) SCANNER BEING USED
fig 2-14 3-D scanner device (A) and sample output (B)
an object on the screen in three dimensions However, these devices require some time to learn to control and are used only in specialized design environments
Another type of input device is the 3-D scanner (Fig 2-14), which originally was expensive but has become very affordable 3-D scanners create a cloud of points in XYZ space that can define an object These clouds of points are processed to create a 3-D model of the original object Ordi-nary scanners can be used to scan in raster-based images of
a drawing or sketch The resulting file is essentially a picture
of the drawing and cannot be used directly in vector-based CAD systems While software exists to convert raster images
of drawings to a CAD vector file, the results are often less than acceptable Scans of design sketches can be used to help provide a background image to aid in modeling on a CAD system
Output Devices Output devices are used to create copies of designs that can
be viewed or read without the need for a computer The most common types of output devices used with CAD workstations are printers Other types of output devices can create photo-graphic images of slides, and some can create 3-D objects directly from the CAD data These devices are used for rapid prototyping The two most common of these devices are stereo lithography apparatus (SLA), manufactured by 3D Sys-tems, Inc (Fig 2-15, p 24), and fused deposition modelers (FDMs), manufactured by Stratasys, Inc These rapid proto-typing systems are essentially 3-D printers
(B) TYPICAL SCANNED OUTPUT
Trang 3924 PART 1 Basic Drawing and Design
Fig 2-15 Stereo lithography
0 Toner is transferred to the charged paper by the drum
C) Hot roller bonds toner to paper
Output tray
Fig 2-16 Laser printer technology
8 Paper is given
a static charge
Most printers currently in use are either laser printers
(Fig 2-16) or printers based on ink-jet technology (Fig 2-17)
Affordable printers can create A-size and B-size prints in high
resolution (600 dpi or greater) in black and white or color
Specialized ink-jet plotters can produce C-, D-, and E-size
plots in full color (Fig 2-18) Many companies still use
pen-based or electrostatic plotters, but these types of plotters are
more expensive than the newer technology and their use in
industry is declining
Software
The typical software components of a CAD system are
the operating system, which controls the common functions
Rotating mirror
1
8 Rotating mirror reflects laser, which projects image of the page onto the rotating drum
of the workstation, a CAD program consisting of one or more application modules, and utility programs used for specialized operation such as file conversion All CAD systems should also include utility programs to protect the
system from intrusive programs, commonly know as viruses, Trojans, and spyware, and programs that can diagnose and
maintain the hardware and software systems, backup data,
or help recover a system in the event of a system failure
Operating Systems
An operating system is software that controls the function of
a system's hardware and the allocation of system resources, such as memory and disk space Most current operating
Trang 40plates control direction
of ink jet spray
Ink fountain
Fig 2-17 (Left) How an ink-jet printer creates an image (Right) Snapshot printers are
popular for digital photographs
Fig 2-18 (Left) Ink-jet printers use a spray system to create simple line drawings or
detailed renderings Shown here is an architectural elevation being printed (Right) A roller
plotter uses a robotic arm to draw with colored pens
systems, such a Microsoft Windows, are windows-based
operating systems that provide the user with a graphics user
interface (GUI), which handles routine functions, including
printing and saving files in a consistent way Operating
sys-tems also control and simplify network access for the user
The common features of a windows environment are
drop-down or tear-off menus defined work areas called
win-dows, and a mouse, which makes it possible to select or move
files The windows environment can be customized to fit the
individual users needs; for example, for the visually impaired, larger text and icons are available, as are various sound prompts and cues
Utility Programs
Utility programs are software that addresses routine
opera-tions not dealt with adequately by the operating system The most common types of utility programs protect the CAD