Engineering Drawing from First Principles Using AutoCAD Dennis Maguire CEng, MIMechE, MemASME, REng. Des, MIED City and Guilds International ChiefExaminerin Engineering Drawing : UTTERWORTH EINEMANN OXFORD AMSTERDAM BOSTON LONDON NEWYORK PARIS SANDIEGO SANFRANCISCO SINGAPORE SYDNEY TOKYO Butterworth..Heinemann An.imprintofElsevierScience LinacreHottse,JoroanHill,OxfordOX28DP 200WheelerRoad,Burlingtofl,MA01803 Firstpublished1998 Transferredtodigital.printing2003 Copyright©.·1998,DennisMaguire.Al1rigntsreserved Nopartofthispublication>may.hereproducedin>any.materialform•.(including pbotocopyin.g>orstoringinanymediumbyelectronicmeans andwhether arnottransientlyorincidentallytosomeotheruseofthispublication)without the>wri1ten.permission.ofthe.cop~rightholder.except.in.accordancewiththe provisiQnsofthe Copyright,DesignsandPatentsAct1988orunderthetermsof 1:1licenceissuedbythe CopyrightLicensingAg:encyLtd,90Tottenbam.>CourtRoad, London,EnglandWlT4LP.•Application~for thecopyrightholder'swritten permissiontQreproduceanypartofthispublicationshouldbeaddressed tothepublisher Whilsttheadviceandinformationinthisbookisbelievedtobetrue.and.aceurate at••thedate..ofgoingtopress,.neitherthe...authornotthe.•publishercan.accept.any l~ga.lre.sppDsibilityorliability>foranyerrorsoromissionsthatmaybemade British.LibraryCata.loguinginPnbJicati()nData AcataloguerecordfQ.ttl1is.bookisavailablefrornthe<BritishLibrary LibraryofCongress>CataloguinginPublicationData Acata.loguerecordforthisbookisavailablefrotfitheLibraryofCongress ISBN0340691980 ForInformationonallButterworth,..Heinemannpublications visit.ourwebsitearwww.bh.eom Preface Thank you for your interest. My first introduction to the subject of technical drawing came at school, whenat theage of11, we startedwoodworklessons. Atthe firstmeeting of the class Mr Munday, our teacher, told us that we would draw working plans of a simplejoint. Wewereintroducedto a drawingboard, tee square, set ofinstruments, one sheetofsnowywhitepaperandtwo paperclips.Wewere showntheprinciplesofsimple projection and then proceeded to copy views of a Lap Joint from the blackboard. I instantly found this to be a very agreeable relaxing exercise. The controlled use of the pencil, rule, square and compasses also enabled those of us without natural skills in freehand art and painting to be 'in with a chance'. Atthe nextlesson we were taughthowto prepare the wood, cut andmakethetwo parts andfinally checkthe accuracyoftheassembledjoint.Inadditionwe could seeeveryedge and corner representedby lines on the drawing. This particular subject at school was especially popular with the other lads and the general class atmosphere very stimulating and rewarding. When the results compared favourably with the initial drawings I felt that I had really achieved something and soon developed a strong desire to continue studies. We all also took great pride in trying to keep the paper nice and clean and free of pencil smudges. I also always enjoyed the subject of Applied Geometry which islogical and required more construc tional work on the drawing board. When I left home in the mornings for school it was not uncommon to see a new neighbour ofours leaving for work. He was smartly dressed and carried a leatherbrief case.Out ofcuriosityIaskedmy motherwhatMrOramdidforaliving andshe foundout thathe was a draughtsmanandmade 'plans'. Idecidedthatthis was quite alikely career forme andit certainlygave me some sense ofpurpose at school whenIrealisedthatyou could actually get paid good money for doing something you really enjoyed. I later bought a small drawing board and tee square for use at home and copied examples from books in our local library and found that regular practice soon improves technique. Pencil drawings are easily corrected but damage to the paper may arise. More impor tant drawings for manufacturing and publication purposes were required to be pro duced in ink. This was a skill requiring lots of patience because ink is reasonably permanent and extensive errors on some surfaces needed a redraw. In industry, it was not uncommon for ink tracers to be employed to trace over pencil drawings onto transparent film after original designs had been produced, checked and approved. These days with the aid of a computer it is not necessary to worry about the state of the paper or the need to trace the finished designs to obtain a truly professional result. No need to keep sharpening the pencil to obtain consistent line thicknesses, no need to worry about spelling mistakes after you have inked in notes when you have otherwise nearly finished your work of art. Variations in the height and slope of letters and numbers during dimensioning always used to separate the beginnerfrom the professional and often spoil an otherwise sound drawing. These days lines andletters are allstandardisedanda spell checkeravailable at the touch of a button, but it is still necessary for the draughtsman to be completely in Preface vii charge. We have not reached the stage where the computer can dispense with the draughtsman. This fact needs to be broadcast very widely and regularly. It is definitely notsufficientto onlybecomeaproficientkeyboardoperator. Computerscannotconceive and produce original designs and drawings. With the aid of a computerthough you can produce clear unambiguous drawings provided you adhere to the appropriate National and International Standards. This is the area where I hope to assist you and I am convinced that to develop your talents you must keep your hands on the keyboard. In the following pages are exerciseswhichIam sure will putsome basic knowledge and skillsintoyourfingersandalsohelpgeneratesomedraughtingspeed.Donotworryorget disheartenediftheresultsare alittle slowin coming- withcomputingithappenstousall. As the title suggests, this book is about the production of drawings from basics. All of thesedrawingshavebeenpreparedwiththeaid ofthe computerbutofcoursethereisno reasonwhyyou couldnotredrawthemona drawingboardifyou sowish, asthis would certainly develop manual ability and gain a clear understanding of the principles of Engineering Drawing. Not all drawing offices use CAD. I started to teach this subject at evening classes in Hayes and the first drawing office I walked into had the following words printed on a strip of paper above the blackboard: 'Little things make perfection, but perfection is no small thing'. Asfar as draughtsman ship isconcernedthereisalot oftruthinthis shortstatement.Inthemselves, therulesare relatively simple but they need to be employed accurately and consistently, and applied thoroughly. The draughtsman also needs to be a quick and efficient operatorand hence the value of practice. The computer provides a range of facilities which are available for selection by the operator and often allows a job to be done in several different ways. With experience you will make your own pet choice ofmethods and hopefully achieve the same results. These graded examples start from a completely blank screen. I hope you will soon develop confidence and enjoy draughting with the aid of the computer. Please note thatjob vacancies are equallyavailable in drawing offices for bothsexes soI wish to apologise for using the widely used collective noun of 'Draughtsman' to cover Drawing Office Personnel. It definitely implies equality of status and it is a pleasure to find an increasing number of young ladies enjoying employment in the drawing office. Thankyouagainfor readingthis book. Iwishyouwell andeverysuccess in yourstudies and career. The British Standards Institution was the world's first national standards body and there are over 80 similar organisations world-wide which belong to the International Organisation for Standardisation (ISO). BSI represents the interests and views of British Industry. The first editionofBS308 to coverEngineeringDrawingPracticewas publishedin 1927. It is currently published in three separate sections and available in reference libraries throughoutthe country. The BSIcataloguelistsover 10,000publicationsandaYearbook is usually available in reference libraries. Eachyear new or revised standards are issued to keepthetechnicalcontentsup-to-date. Revisionsencompassnewmaterials, processes and technologies. Further information on BSIservices can be obtained from: BSIEnquiry Department, Linford Wood, Milton Keynes MI<146LE. Tel:0908 221166. AcompletelyrevisededitionofAManualofEngineeringDrawingPracticehasbeenissuedto viii Preface include an extensive range ofimportant applications ofBSandISOstandards whichare relevantto currentdraughtingpractice.Thisusefulreferencebook alsoincludesdetails of generaldrawingofficepracticeandadditionaldraughtingexamplesfrom manybranches of technology. Dennis Maguire January 1998 Acknowledgements I express my thanks to the British Standards Institution, 389 Chiswick High Road, London W4, for kind permission to reprint extracts from their publications. I have enjoyed a long and enjoyable association of over 35 years with The City and Guilds of London Institute, 1 Giltspur Street, London EClA 9DD,and am grateful for their kind permission to include past examination questions in this book. I also thank my friend and colleague Colin Simmons for much helpful information and guidance. The friendly advice and assistance given to me by DilysAlam, Sian Jones and staffat Arnoldisalso verymuchappreciated. My thanks to Ray for muchtechnical help andhisinvaluablesupportwithmy computerequipment, andtoBrianfor otherdrawing examples. Finally many thanks to my wife Beryl for her endless patience, encouragement and all her clerical help. Chapter! First steps Bytheendofthis chapter, Ihopeyou willbeable tounderstandthe following commands and perform these activities: • Open the drawing software program. Clickand browse through each of the options on the menu bar in turn and note that many sophisticated and advanced features are available. • Reposition the movable toolbox. • Note standard drawing sizes. • Appreciate Portrait and Landscape orientation ofthe drawing. • Select and position an A4 sizedrawing sheet. • Set Snap and Grid values. • Draw lines between given coordinates. • Operate the ZOOMcommand. • Become familiar with the ORTHO button facility. • Experiment with ERASE and BREAI(commands. • Use the REDRAWcommand to clean up the screen. • Draw circles and arcs. • Use the RUNNING OBJECT SNAP OPTION to draw tangents and position tangency points. • Gain experience with the FILLET feature. • Convert lines and arcs to polylines for finished outlines. • Experimentwith the TEXTcommand. Set text types and sizes. • Note the minimum height ofdrawing characters and text abbreviations. • ExperimentwiththeMOVE,COpyandROTATE commandsandlearnhowto reposition detail. • Experimentwith the ARRAY command. • Choose screen preferences. • Select coloured layers for differentparts ofa drawing. • Note recommended thicknesses for various types oflinework. • Check available printers. Save your drawings with suitable filenames and add drawing numbers. Youwill find that information retrieval is an important part of CADwork. Set up the printer and follow the PRINT/PLOTprocedure to make an A4 copy. Note: In industrialdrawing officesthe drawings relatingtoparticularcontractsare often numbered afteran abbreviated contractname followed by the number. Assume thatwe have a design contract where we would expect 50 or 60 drawings to be needed on a contract from SMITH& CO. Typical drawings could be numbered SMTOOl, SMT002, SMT003, etc. The sequence of drawings you copy from this book could therefore be ACADOOl, ACAD002, etc. Itisalso a regularpractice to keep aDrawingRegister ofnumbers, titles and completion dates sothatothermembersofstaffinanorganisationcan checkon contractprogressand the drawings available. Students often find that starting to learn CAD can be rather slow and the following exercises are thereforedesignedtointroducegraduallyinterestingaspects ofthesoftware 2 Engineering drawinq/1"0111 first principles appliedto usefulengineeringtopics.Bothareas ofworkareprogressivesoeventuallyyou will possess CAD and valuable engineering draughting experience and be sufficiently skilledtotakeyourplaceinamoderndrawingoffice.Itisalsoavitalpartofthestudythat you appreciate the reason for the position of every line and possess the ability to edit freely any section of your drawing. Abigpart ofa draughtman's work is to implement modifications and changesto drawingswhich oftenresultfrom improvementsin design and production techniques. Initial preparations Imustmaketheassumptionthatasoftwareprogram, forexampleAutoCAD LT, has been installedonacomputerandisreadyforyourstudies, sotake acomfortableseat infrontof the keyboard, switch on and select the icon on the Windows Program Manager (Figure 1.1). Double clickwiththeleft-handmousebuttonover theicon andthescreendisplay shown in Figure 1.2 appears under a central heading ofAutoCAD LT-UNNAMED. Please note thatallthefollowing operationsare initiatedbyclickingtheleft-handmouse button. Immediatelybeneath the heading isthe pull-downmenu line which starts with File,thenEdit, Draw, View,Assist,Construct, Modify, Settings andHelp. Clickovereach ofthem in turn and note the various optional functions that are available to appreciate the scope of the program, but please be assured that you can make rapid progress with only a few commands. Thenextline includesthe Toolbarwhichcan bepersonalisedto suit yourownmethodof Figure1.1 First steps' 3 Commend: Figure 1.2 working and arrangedto hold those commands you most regularly use. In the centre of this line youwillfind the co-ordinatedisplay where the positionofthe crosswires on the cursor, whichyou movewiththemouse, are indicated.Twovaluesare given, namelythe X and Yeo-ordinates. The graphics or drawingpartofthe screenareacan representadrawingsheetofany size you wish to use anditistherefore necessary to choose suitable units andscales.Itisour intention here to use only metric dimensions. Setting out lines, arcs and circles I expect you are keen to produce a meaningful drawing so we need to select a suitable drawing sheet. A4 size is acceptable for most printers with dimensions of 210mm X 297mm. Youcan of course use the sheet in two different ways and 'portrait' style will have the horizontal X dimension of 210 and the vertical Ydimension of 297mm. Turn the paper round 90°and we have 'landscape' style where the X dimension is 297 and the Ydimension 210mm. Our computer must first be set for these sizes, so look along the menu list at the top of the screen, click on Settings and the menu shown in Fig. 1.3 will appear. Choose Limitsandnote this message in the commandarea at the bottom ofthe screen. Command: limits Reset Model space limits: ON/OFF/ <Lower left corner> <0.0000,0.0000> Press the <Enter> key, which means that you accept this default value, and this next 4 Engineering drawinq[rom [irst principles Figure1.3 message willappear (Note thatdrawinglimits are alwaysquotedwiththeX andYvalues in alphabetical order): Upper right corner <420.0000,297.0000> This is a default value for a sheet of A3 paper and is double the size we require. Furthermore, it is the wrong way round for portrait style, so type 210,297 and press the <Enter> key. Note that the area at the bottom of the screen links us with the computer to exchange messages. We cannot indicate our next move until the computer shows Command: This message means that it is now ready to receive details of the next operation. After choosing the next event from the dropdown menu, it isnecessary to press the <Enter> key andthe computerthengoes to work. Whenthe operationiscompletethe Command: message will again appear. Please understandthat this symbol <R> or .J means thatyou press the <Enter> key and obviously looks like the key on the keyboard. Having selecteda suitable size ofpaper onwhich to draw, we want it to become visible. This is activated via the Settings pull-down menu by clicking the Drawing Aids dialogue box. The box shown in Fig. 1.4 will appear. Click to turn on the Grid which isa series ofaccurately spaced dots forming a square grid and can convenientlybe used for measuring purposes. Adjust the X Spacing to 10.00 and you will find that the Y SPACING will adjust itself. Clickto turn on the Snap feature. Thisis a most important item, enablingyou topositionexactlythe cursorat specified distancesapartandcertainly speeds up the accurate placing of points on the screen. I suggest that you set an X Spacing of 2.00 and again ignore the Y SPACING. In the Modes column at the left-