dharmd:\N-Design\Des19-1.pm5Fig. 19.22 Castor wheel8936230 33909R96R30R60R42M18DIA3, DRILL939340151531081.514363933109108M18DIA 3,75241842398418M10, DEEP 63333604 HOLES, DIA 10R87108903684R12102Part No.Name Matl. Qty.12345678910Parts listFramePlateHubFlangeTyreBushShaftKing-pinNutBolt with nutCICICIStripsteelRubberBrassCRSCRSMSMS111211112610°10DRILL10
Part Drawings 387dharmd:\N-Design\Des19-1.pm5Fig. 19.23 Speed reducer911521014415113168371262 HOLES, DIA 665 TEETH, 5 MODULEPCD 1755 512015518542024406645187513 TEETH, 5 MODULEPCD 658 HOLES,DIA 82 MODULEPCD 4012301534230411250178 4070°36105430302 MODULEPCD 1804013518530206563490163046288 HOLES,M83 MODULEPCD 13220 20Sl. No.NameMatl. Qty.123–56–89, 10Sl. No.NameParts listBodyEnd supportShaftsSpur gearsBevel gearsCICIMCSMCSMCS113321112, 13141516PulleyBearingsOil sealsBearing coversBearing retainerMatl. Qty.MSRubberCI—16451
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dharmd:\N-Design\Des19-1.pm519.4.6 Castor WheelCastor wheels are used on trolleys for moving them in any direction with minimum effort. Acastor assembly is shown in Fig. 19.22. It consists of a frame 1 made of cast iron. The frame isfreely suspended from the plate 2 by king-pin 8 and nut 9. The assembly is kept intact by a split-pin. The brass bush 6 is pressed into the hub 3. The rubber tyre 5 is placed on the hub and keptin position by the two flanges 4 which are clamped by bolts 10. This wheel assembly is located inthe frame by the shaft 7. The shaft is positioned with a nut and a split-pin. A grease nipple is fixedon the head of the shaft, to provide lubrication between the shaft and bush bearing.19.4.7 Speed ReducerGear trains are used for transmitting power and also to change the speeds between two or moreshafts. Figure 19.23 shows a speed reducer in which bevel gears and spur gear trains are used toobtain speed reduction. It consists of the gear box body 1 to which is fixed the end support 2. Thespur gear 7 is fixed on the shaft 3 along with the roller bearings 12 and 13. The driven gear 6 isthen keyed in position.The bevel gear 9 and spur gear 8 are mounted on the shaft 4 along with the bearings at theends. The bevel gear 10 is mounted on the shaft 5 along with the bearings. The driver pulley 11 isfixed with a key on this shaft. The speed reduction takes place in two stages between the bevelgears 10 and 9 and between spur gears 8 and 7.The bearings are provided with bearing covers 15, oil seals 14, bearing retainer 16, andcirclips wherever necessary. Eight tapped holes of M8 and free holes of φ 8 are provided on the bodyto fix the cover. The holes of φ 6 are made in the body for dowel pin location.ExerciseThe assembly drawing of a speed reducer is shown in Fig. 19.23. Draw the details of the following,to suitable scale🙁i) End support 2, (ii) Shaft 4, (iii) Spur gear 7, (iv) Bevel gear 9, and (v) Bearing cover 15.
20.1 INTRODUCTIONA production drawing, also known as working drawing, supplies information and instructions forthe manufacture or construction of machines or structures. A production drawing should provideall the dimensions, limits, special finishing processes, surface quality, etc. The particulars ofmaterial, the number of components required for the assembly, etc., are given in the title block.The production drawing of a component should also indicate the sub-assembly or main assemblywhere it will be assembled.Since the working drawings may be sent to other companies to make or assemble the unit,the drawings should confirm with the standards followed in the country. For this reason, aproduction drawing becomes a legal document between the parties, in case of disputes inmanufacturing.Working drawings may be classified into two groups : (i) detail or part drawings and (ii)assembly drawings.20.2 TYPES OF PRODUCTION DRAWINGS20.2.1 Detail or Part DrawingsA detail or part drawing is nothing but a production or component drawing, furnishing completeinformation for the construction or manufacture of the part. This information may be classifiedas:1. Shape description This refers to the selection of number of views to describe the shapeof the part. The part may be drawn in either pictorial or orthographic projection; the latter beingused more frequently. Sectional views, auxiliary views and enlarged detailed views may be addedto the drawing in order to provide a clear image of the part.2. Size description Size and location of the shape features are shown by properdimensioning. The manufacturing process will influence the selection of some dimensions, suchas datum feature, tolerances, etc.3. Specifications This includes special notes, material, heat treatment, finish, generaltolerances and number required. All this information is mostly located near the title block.4. Additional information Information such as drawing number, scale, method ofprojection, date, names of the parts, the draughter’s name, etc., come under additional informationwhich is included in the title block.Since the craftsman will ordinarily make one component at a time, it is advisable to preparethe production drawing of each component, regardless of its size, on a separate sheet. Figures 20.1and 20.2 show the detailed drawings of a template jig and gear.38920PRODUCTION DRAWINGS
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dharmd:\N-Design\Des20-1.pm5Fig. 20.1 Template jig12 3 4 5 6ADABD12 3 4 5 64 × 90°4 HOLES,DIA 10f 95f 600.18M MAB2 × 45°B0.05ACC0.08–0.0025–0.05SCALETITLETEMPLATE JIG-DRG No.MD 24.1MATL TOLERANCEFINISH2512.5NAMENAMEDATECA– 0.0012– 0.25R3
Production Drawings 391dharmd:\N-Design\Des20-1.pm5Fig. 20.2 Gear1234234ABCDEFABEFf0.06A2.51.252.51.25Af50 H7f7553.8+0.12 × 45°3 CHAMFERS0.1A12.512.51.6 × 45°2 CHAMFERS0.25A3050Number of teeth Z 50Module m 3Helix angle 16°RHbD rectioni14 Js9±0.02f50 H7+0.000+0.025Hardness BHN 240–280NAME DATEMATL.STEEL45 CTOLERANCE± 0.5FNSHII2512.5SCALETITLEHELICALGEARDRG No.PD. 24–2f161.82–0.00–0.08+0.014Js9
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dharmd:\N-Design\Des20-1.pm520.2.2 Working Assembly DrawingsIt is usually made for simple machines or jobs, consisting of a relatively smaller number of simpleparts. All the dimensions and information necessary for the manufacture of a part and for theassembly of the parts are given directly on the assembly drawing. Separate views of specific parts,in enlargement, showing the mating of parts, may also be drawn, in addition to the regularassembly drawings. Figures 20.3 and 20.4 show the detailed assembly of a tea-poy and crankassembly respectively.Fig. 20.3 Detailed assembly drawing20.2.3 Detailed Drawings and Manufacturing MethodsThe type of manufacturing process influences the selection of material and detailed features of apart (Fig. 20.5). As shown in Fig. 20.5a, if the component has to be cast, then rounds and filletsare to be added to the part. Additional material will also be provided where surface requiresfinishing.Several drawings may be made for the same part, each one giving only the informationnecessary for a particular stage in the manufacture of the part. A component which is to beproduced by forging, for example, may have one drawing showing the forged part (Fig. 20.5b) withno machining details and a separate drawing for the machining of the forging (Fig. 20.6).
Production Drawings 393dharmd:\N-Design\Des20-1.pm5Fig. 20.4 Crank20.3 EXAMPLE20.3.1 Petrol Engine Connecting RodConnecting rod assembly of a petrol engine, the big end of which is split into two halves is shownand described in Chapter 19 (Fig. 19.1).The component drawings of the above assembly are shown in Fig. 20.7, with details oftolerances, surface finish, etc., as required for production work. The rod and cap are made offorged steel and machined to close tolerances at both the big end as well as the small end asshown. The bearing brasses are made of gun-metal, because it has good resistance to corrosion.
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dharmd:\N-Design\Des20-1.pm5Fig. 20.5Oil groove is provided at the centre of the bearing. The bearing bush is made of phosphor bronze,to provide low coefficient of friction. Oil groove is provided in the bush for lubrication between thepin and bearing. The bore of the bush is given a tolerance to have a close sliding fit with thegudgeon pin. The external diameter is provided with positive tolerance on both the limits toensure interference fit with the small end of the rod. The square headed bolts (5) and castle nuts(6) are used as standard components.
Production Drawings 395dharmd:\N-Design\Des20-1.pm5Fig. 20.6THEORY QUESTIONS20.1 What is production or working drawing of a component?20.2 What information must be provided on production drawing of a machine to facilitate its manufac-ture and assembly.20.3 Why working drawings must be prepared as per the standards?20.4 Classify and describe the various types of working drawings.20.5 What is a working assembly drawing?20.6 What kind of drawings are to be prepared for producing, (a) forged component, and (b) castcomponent.DRAWING EXERCISES20.1 Prepare working drawings of the following components of the split sheave eccentric, shown inFig. 19.7.(a) Sheave piece (1)(b) Sheave piece (2), and© Strap (7).Indicate the fits and tolerances recommended for the above components.20.2 Make the working drawings of the components of the angle plummer block, shown in Fig. 19.21.Indicate suitable fits and the corresponding tolerances for the parts: (a) Brasses and base, (b)Brasses and the shaft (not shown).20.3 Study the lathe speed gear box shown in Fig. 19.10a and make a working drawing of the spindle.Indicate the tolerances, surface finish, etc., wherever necessary.20.4 Study the milling machine tail-stock shown in Fig. 19.11 and prepare the production drawings of,(a) body (1), (b) centre (2), and © screw (4). Indicate the fits and the corresponding tolerances onthe body and centre. Write down the process sheet for making the body.
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dharmd:\N-Design\Des20-1.pm5Fig. 20.7 Details of petrol engine connecting rod
39721.1 INTRODUCTIONEngineering drawing, in general is applied to drawings for technical use and is concerned withthe direct graphical representation of designs for physical objects, as used in engineering andscience. Computer aided draughting on the other hand, is the application of conventionalcomputer techniques, with the aid of data processing systems, to present a graphical solution.It deals with the creation, storage and manipulation of models of objects and their pictures. Theuser generates graphics by interactive communication with the computer. Graphics are displayedon a video display and can be converted into hard copy with a plotter or printer.Presently, there are many independent graphics software packages available for usewith micro-computers. Graphics package is a set of functions, which are called by the user in hisapplication program to generate the drawings and pictures. AutoCAD was developed to run onany micro-computer system.Interactive computer graphics helps in developing simulation models of real life systems,where a lot of risk is involved otherwise. For instance, flight simulators can be used to train thepilots before handling the actual planes.21.2 OVERVIEWAutoCAD provides a set of entities for use in constructing the drawing. An entity is a drawingelement such as a line, circle, etc. By typing a command on the keyboard or selecting it from amenu, the entity can be drawn. Parameters should be supplied for the chosen entity in responseto the prompts on the screen. The entity is then drawn and appears on the screen. The effect ofevery change made appears on the screen immediately.These entities may be erased or moved or copied to form repeated patterns. Theinformation about the drawing also may be displayed.21.3 REQUIRED EQUIPMENTComputer aided graphics systems have three major components: the draughter, hardware andsoftware. The physical components of a computer constitute the hardware, such as computerterminal, input devices and output devices. Software is the draughter’s instructions to thecomputer.21.3.1 ComputerComputers execute the instructions in the input after receiving the input from the user andthen produce output. These are classified by size, viz., main frames, mini-computers and micro-computers.21COMPUTER AIDEDDRAUGHTING
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dharmd:\N-Design\Des21-1.pm521.3.2 TerminalIt consists of a keyboard, a cathode ray tube and inter-connections with the computer. Theterminal allows the user to communicate with the system.21.3.3 KeyboardKeyboard generally resembles typewriter and normally contains many functional keys. Thispermits communication through a set of alphanumeric and functional keys.21.3.4 Cathode Ray Tube (CRT)A CRT is a video display device, consisting of a phosphor coated screen and electron gun. Theelectron gun throws a beam and sweeps-out raster lines on the screen. Each raster line consistsof a number of dots called pixels. By turning the pixels on and off, the images are generated onthe screen. One measure of quality of picture produced on the screen is resolution and for goodquality of graphics to be drawn, high-resolution screens are used.21.3.5 PlottersThe plotter makes a drawing as instructed by the computer. Flat bed plotters and drum typeplotters are in vogue. Both black and white and colour graphics can be made by the use ofdifferent pens.21.3.6 PrintersInexpensive impact type of printers, dot matrix printers have rectangular print heads, composedof pins which can be manipulated to form a character. These patterns of pins make dottedcharacters on paper, when they are forced against ribbon. The output of the dot matrix printersis of low quality and hence they find limited use in graphics applications. These printers areused especially when continuous paper is fed. Ink jet and laser printers are now-a-days usedwhich may be able to print on A4 size cut sheets. The print quality is very good and both linesketches and photographs can be printed. For the purpose of desktop publication, these printersare recommended.21.3.7 DigitizersA drawing may be scanned after placing it on the digitizer, thereby converting the picture to adigital form, based on the x, y co-ordinates of individual points. These drawings can also bestored for later use or corrected/modified. Thus, a digitizer is a graphics input device to thecomputer for display, storage or modification.21.3.8 Locators and SelectorsThese devices enable the user to interact with the computer, in a more natural way. The locatorsgive the position information. The computer receives the co-ordinates of a point from a locator.The examples are thumb wheels, joystick, mouse, track balls, etc. The selectors are used to picka particular object, but no information is provided about its screen position, eg., light pen.21.4 DISPLAY TECHNOLOGYIn co-ordinate geometry, a line segment consists of infinite number of points whereas in computergraphics a segment has a finite number of pixels. A pixel is the smallest screen element, whichcan be specified individually. The entire screen resembles a two dimensional array of pixels.These points are addressed by their x and y co-ordinates; the value of x increases from left toright and y likewise from bottom to top. Displays have been built with as many as 4096 × 4096addressable points and with as few as 256 × 256. The particular points, which lie on the linesegment selected, are displayed with the required intensity. This means that they cannot bepositioned with infinite precision.
Computer Aided Draughting 399dharmd:\N-Design\Des21-1.pm521.4.1 Plotting the DrawingsAutoCAD drawing may be plotted either by a pen plotter or a printer plotter. Pen plotters arevery accurate and multiple colours may be obtained. Printer plotters have limited resolutionand smaller paper sizes and produce monochrome output. However, printer plotters are usuallyfaster than pen plotters. For pen plotter, PLOT command is used, whereas for a printer plotter,PRPLOT command is used.While beginning a plot from the main menu, tell AutoCAD, which portion of the drawingto be plotted. Specify the part of the drawing to be plotted by entering: Display, Extents, Limits,View or window: the response specifies a rectangular area of the drawing.By Specifying😃 (Display) — this option plots the view that was displayed in the current viewport just prior to the last SAVE or END command for that drawing.E (Extents) — this option is similar to ZOOM extents. The extents are updatedautomatically as one draws new entities.L (Limits) — plots the entire drawing area as defined by the drawing limits.V (View) — plots a view that was previously saved, using the drawing editor’sview command.W (Window) — plots any portion of the drawing. Specify the lower left corner andupper right corner of the area to be plotted.21.5 BASICS OF OPERATING SYSTEMOperating system falls in the category of system software. An operating system is a set ofprograms designed to manage the entire operations of computer system. Basically the operatingsystem performs two fundamental tasks for the computer🙁i) managerial task (ii) interface taskThe operating system does not do any specific task, but it is a general program whichassists the user by doing the following operations:— Controlling all the operations including input/output operations, arithmetic operationsand internal transfer of information.— Communicating with peripheral devices (printer, disk and tape device).— Supporting the running of other software.One can say that the computer system without an operating system is like an officewithout a manager.21.6 STARTING AutoCADOnce AutoCAD 2004/05 software is located on to the computer and the operating system isavailable, one can start using the facility. Soon the computer is turned on, the operating systemis automatically loaded. Various application icons appear on the windows screen. AutoCAD canbe started by double-clicking on the AutoCAD icon available on the desktop of the computer.The various components of the initial AutoCAD screen are as shown in Fig. 21.1 andFig. 21.2 consisting of :1. Drawing Area The drawing area covers a major portion of the screen. Various objectscan be drawn in this region by the use of AutoCAD commands. The position of thepointing device is represented on the screen by the cursor. On the lower left corner, acoordinate system icon is present. On the top right corner, standard windows buttonsare also available.2. Command Window At the bottom of the drawings area, command window is presentand commands can be entered by keyboard.
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dharmd:\N-Design\Des21-1.pm53. Status Bar At the bottom of the screen, status bar is displayed, which will make it easyto change the status of some AutoCAD functions by proper selection.4. Standard Tool Bar Standard tool bar displays coordinates and they will change onlywhen a point is specified. The absolute coordinates of the cursor will be specified withrespect to the origin.5. Snap Snap mode allows the cursor to be moved in specified/fixed increments.6. Grid By choosing this button, grid lines are displayed on the screen and can be used asreference lines to draw AutoCAD objects.7. Ortho By selecting the orthomode, lines can be drawn only at right angles on the screen.8. Polar The movement of the cursor is restricted along a path based on the angle set asthe polar angle. One can use either polar mode or orthomode only at a particular time.One can also use function keys for quick access to certain commands. Only important functionsdefined by AutoCAD 2004 are given below:Function Key FunctionF1 Online helpF2 Toggles between command window on and offF5 Switches among Isoplanes Top, right and leftF6 Toggles between coordinates on and offF7 Toggles between grid on and offF8 Toggles between orthomode on and offF9 Toggles between snap mode on and offF10 Toggles between Polar tracking on and off21.6.1 Invoking AutoCAD CommandsAfter starting AutoCAD and when the cursor is in the drawing area, to perform an operation,commands must be invoked. The following methods are provided to invoke the commands.1. Keyboard Using keyboard, command name can be typed at the command prompt andby pressing ENTER or SPACE BAR, the command can be invoked.2. Menu The menu bar is at the top of the screen which displays the menu bar titles. Asthe cursor is moved over this, various titles are highlighted and by means of pick button,a desired item can be chosen. Once it is selected, the corresponding menu is displayeddirectly under the title. A command can be invoked by picking from this (Fig. 21.3a).3. Draw Toolbar This is an easy and convenient way to invoke a command. This isdisplayed on the left extreme of the initial AutoCAD screen (Fig. 21.3b) and very easy tochoose by picking.4. Tool Palettes These are shown on the right side of the monitor screen (Fig. 21.2). Aneasy and convenient way of placing blocks/patterns of hatching in the present drawing.By default, AutoCAD displays the tool palettes on the right of the drawing area. Varioushatching patterns also can be selected from this.21.6.2 Interactive TechniquesDeveloping a drawing by AutoCAD is done by interactive technique, so that it is easy to follow andachieve the results. The popular interactive techniques are layers, drawing insertion, objectsnap, zooming, panning, plan view and 3D views, view ports, resolution, editing the drawingand many more.
Computer Aided Draughting 401dharmd:\N-Design\Des21-1.pm5Fig. 21.1Fig. 21.2
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dharmd:\N-Design\Des21-1.pm5Fig. 21.3 (a) Invoking the ELLIPSE 21.3 (b) The Draw toolbarThe layering concept is similar to the transparent overlays used in many draughtingapplications. This allows the user to view and plot-related aspects of a drawing separately or inany combination. In drawing insertion, a drawing can be stored in a drawing file and this maybe inserted in subsequent drawings for any number of copies. To refer to geometric features ofexisting objects when entering points, the object snap may be used. The visual image of thedrawing on the screen may be magnified or shrunk by zooming. Whereas, panning allows viewingdifferent portions of the drawing, without changing the magnification. In plan view, theconstruction plane of the current user co-ordinate system is parallel to the screen. The drawingmay also be viewed from any point in space (even from inside an object). The graphics area ofthe screen can be divided into several view ports, each displaying a different view of the drawing.Physical resolution refers to the amount of detail that can be represented. This resolution canbe changed at any time. The editing facilities of AutoCAD make it easy to correct or revise adrawing. Multiple copies of an object, arranged in rectangular or circular patterns are easy tocreate.21.7 PLANNING FOR A DRAWINGWhile planning a drawing in Auto CAD, one has to organize some of the information such aschoosing the units, co-ordinates, etc.21.7.1 Co-ordinate SystemThe system used by all the CAD packages is generally the rectangular cartesian co-ordinatesystem designated as x, y and z axes. The positive direction of these axes follows the right handrule. Any point in space can therefore be designated by the co-ordinate values of these 3 axes.viz., x, y and z.
Computer Aided Draughting 403dharmd:\N-Design\Des21-1.pm5The co-ordinates can be input into the system by🙁i) The direct input of co-ordinate values in the respective order of x, y and z. If z co-ordinate is not mentioned, then the values are assumed to be at a single given level.(ii) Specifying the co-ordinates in an incremental format from the current cursor posi-tion in the drawing area. The distance is specified by using @ parameter before theactual values. The incremental values apply to all the ordinates.(iii) Point co-ordinates may also be specified using the polar co-ordinate format. It canalso be an extension of the incremental format.(iv) Using the mouse button, the cursor may be taken to the required position and thebutton is clicked.It is generally necessary to specify the limits of the drawing with the help of the commandLIMITS, where the user will be asked to specify the lower left corner and upper right corner ofthe drawing sheet size. This establishes the size of the drawing.21.7.2 Basic Geometric CommandsBy way of choosing the basic commands in AutoCAD, one can make simple drawings. Thevarious entities that can be used for making an AutoCAD drawing in 2D are: point, line, ellipse,polygon, rectangle, arc, circle, etc.Generally AutoCAD provides a default option as <> in each of the command response.The value shown in the angle brackets is the most recently set value. To have the same value,one has to simply press the <Enter> key. The various options available for each command areshown in the command window. But the user need to respond by choosing one letter in mostcases, which makes the AutoCAD choose the right option.21.7.3 Drawing Entity-POINTThe point command locates a point in the drawing.Command: POINT (one has to give the location)POINT: 25, 45 location of the point. Thus, a point is placed at the given location (25, 45).After setting the limits of the drawing, the following drawing aids/tools may be used tolocate specific points on the screen (electronic drawing sheet).ORTHO Command—this is orthogonal drawing mode. This command constrains the linesdrawn in horizontal and vertical direction only.Command: ORTHOON/OFF <current>:SNAP Command—this command is used to set increments for cursor movement. If thescreen is on SNAP mode, the cursor jumps from point to point only. The cursor movement canbe effectively controlled using the SNAP command. This is useful for inputting the data throughdigitizer/mouse.Command: SNAPSnap spacing or ON/OFF/Aspect/Locate/Style <current>: 0.1 (default)GRID Command-working on a plain drawing area is difficult since there is no means forthe user to understand or correlate the relative positions or straightness of the various objectsmade in the drawing. The command enables to draw dotted lines on the screen at pre-definedspacing. These lines will act as graph for reference lines in the drawing. The grid spacing can bechanged at will. The grid dots do not become part of the drawing.Command: GRIDGrid spacing or ON/OFF/Snap/Aspect <0>: 0.5 (default)
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dharmd:\N-Design\Des21-1.pm5Function keys may create drawing aids/tools also. The function keys F7, F8 and F9 act astoggle keys for turning ON or OFF of GRID, ORTHO and SNAP tools respectively.HELP Command—AutoCAD provides with complete help at any point of working in theprogram. HELP can be obtained for any of the individual commands. Most of the informationrequired by the user is generally provided by the help which is always instantaneous.SAVE Command—AutoCAD provides the following commands to save the work/drawingon the hard disk/ floppy diskette:SAVE SAVEAS QSAVECommand: SAVESave drawing as <current name>: KLNI21.7.4 Drawing Entity-LINELines can be constrained to horizontal/ vertical by the ORTHOcommands. CLOSE option uses the starting point of the firstline segment in the current LINE command as the next point.1. Lines can be drawn using co-ordinate system(rectangular cartesian co-ordinates). To draw arectangle (Fig. 21.4a):Command: LINEFrom point: 10, 20 ↵To point: 40, 20 ↵To point: 40, 60 ↵To point: 10, 60 ↵To point: ↵2. It is also possible to specify the co-ordinates inthe incremental format as the distances from thecurrent cursor position in the drawing area. Thedistance is specified by using the @ parameterbefore the actual value. To construct a triangleof given altitude (30) and base (40) (Fig. 21.4b):Command: LINEFrom Point: 10, 20 ↵To point: @ 40, 0 ↵To point: @ – 20, 30 ↵To point: ↵3. It is also possible to specify the point co-ordinateusing the ploar co-ordinate format. To construct ahexagon (Fig. 21.4c) of side 30:Command: LINEFrom point: 10, 20 ↵ (A)To point: @ 30<0 ↵ (B)To point: @ 30<60 ↵ ©To point: @ 30<120 ↵ (D)To point: @ 30<180 ↵ (E)To point: @ 30<240 ↵ (F)To point: close(40, 60)(10, 60)(10, 20) (40, 20)(a)(30, 50)(10, 20) (50, 20)(b)Fig. 21.4CFEDAB(10, 20)©240° 180°120°60°
Computer Aided Draughting 405dharmd:\N-Design\Des21-1.pm521.7.5 Drawing Entity-ELLIPSEThis command allows one to draw ellipses or egg shaped objects. From Release 13 onwards,ellipse is treated as a separate entity. The methods available for making ellipses are:1. By means of axis end points: (Fig. 21.5a)Command: ELLIPSE <axis end point 1>/ center: point ↵Axis end point 2: (point)Axis end pointAxis endpoint 1Axis endpoint 2(a)Axis end pointAxis endpoint(b)CentreFig. 21.5<other axis distance>/ Rotation:Now, if the distance is entered, AutoCAD interprets it as half the length of the other axis.2. By means of centre, axis end points (Fig. 21.5b)Command: ELLIPSE <axis end point 1>/ centre: C ↵Centre point and one end point of each axis should be provided for the response of theAutoCAD.21.7.6 Drawing entity-POLYGONThis option permits to make/draw polygons from 3 to 24 sides in a number of ways:1. For making inscribed/circumscribed polygon with a side parallel to x-axis: (Fig. 21.6a, b)(100, 200)(a) Inscribed(100, 200)(b) CircumscribedFig. 21.6Command: POLYGONNumber of sides: 8Edge/ <centre of polygon>: 100, 200 ↵Inscribed / circumscribed about a circle (I/C): I or C ↵Radius of circle: 80
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dharmd:\N-Design\Des21-1.pm52. With edge option, specifying the size of the edge andorientation: (Fig. 21.7)Command: POLYGONNumber of sides: 7Edge/<center of polygon>: E ↵First end point of edge: 15, 15 ↵Second end point of edge: 15, 30 ↵ The above and various other entities that can be usedfor making an AutoCAD drawing may also be selectedfrom the tool bar.21.7.7 Drawing Entity-RECTANGLEA rectangle is a polygon based on two opposite cornerpoints, known as diagonal points (Fig. 21. 8).Command: RECTANGLEFirst corner: 10, 15 ↵Second corner: 60, 50 ↵ Or from the tool bar menu icon, the pointing device can drag the rectangle and therectangle can be completed.21.7.8 Drawing Entity-CIRCLECircle command offers several methods for drawing circles, the default being to choose a centrepoint and enter or pick a diameter or radius (Fig. 21. 9).R2BCentre, radiusCentre, diameterf403-points2-points21RTTR-OptionFig. 21.9Command: CIRCLE1. 3P/ 2P/ TTR/ <centre point>😛ick a centre point or enter an option(15, 30)(15, 15)Fig. 21.7(60, 50)(10, 15)Fig. 21.8
Computer Aided Draughting 407dharmd:\N-Design\Des21-1.pm52. Diameter/ <Radius><current default>: select D or R3. 3P (3 point) option: one is prompted for a first, second and third point. The circle willbe drawn to pass through these points.4. 2p (2 point) option: one is prompted for the selection of two points which form theopposite ends of the diameter.5. TTR option: allows one to define a circle based on two tangent points and a radius.The tangent points can be on lines, arcs or circles.21.7.9 Drawing EntityARCArc command permits to draw an arc, using a variety of methods.Command: ARC1. Centre/ <start point>: pick a start point using mouse or select C for more options.2. Centre/End/ <second point>: pick a second point of the arc or select C, if option is C.3. Angle/length of chord/end point: pick end point of the arc, if option is E.4. Angle/Direction/Radius/ <centre point>: pick end point of the arc or specify the option.Options (Fig. 21. 10.)Angle — “included angle” prompt appears, to enter the value.Centre — enter the location of an arc’s centre point-at the prompt centre-pick apoint,Direction — enter a tangent direction from the starting point of an arc. At this prompt,pick a point with cursor.End — at this prompt, pick the end point of the arc.Length — enter the length of a arc’s chord. At this prompt, enter a length or dragand pick a length with cursor.Radius — at the prompt “radius”, enter a radius value.Start point — enter the beginning point of an arc.21.8 OBJECT SELECTIONEditing capabilities are the most useful part of AutoCAD system, by making use of the alreadyexisting drawing. For the purpose of editing an object, it is necessary to make selection of theobjects in the drawing. There are various options available for the selection of an object:1. Pick box—the cursor is converted to a small box/square, called pick box. By pressingthe left button of the mouse when the pick box touches an entity, the object can beselected for editing.2. Window option—a single or group entities can be selected by bringing them fully insidea rectangular window. Entities, which lie only partially inside the boundaries of window,will not be selected. Rectangular window may be created by picking the first corner, bypressing the left button and then moving the mouse to the desired position of diagonallyopposite corner. Selection of the object is complete, by pressing the button again.
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dharmd:\N-Design\Des21-1.pm51233-point23Centre, start, end11Start, centre, angle321Start, centrelength (of chord)2312angleStart, end, angle12Start, end, angleRadius1Start, end, direction2313Start, centre, end2Centre, start, angle12angleCentre, start, length12Length ofchordFig. 21.1021.8.1 Edit CommandsThe commands used for modifying the drawings fall under this category. Using these commands,the objects may be erased, retrieved, moved to another location, made into multiple copies,rotated, enlarged, mirror imaged, part of a drawing may be moved and the above effects canalso be reversed (undo).ERASE Command—this lets the entities to be permanently removed from the drawing.The command format isCommand: ERASESelect objects: (desired objects) once it is entered, the objects/portion of the object is erased/deleted.OOPS Command—this restores the entities that have been inadvertently ERASED.Whenever ERASE command is used, a list of entities erased is retrieved by this command.Command : OOPSOnce it is entered, it restores all the entities erased by the recent ERASE command.Once another ERASE is done, the list of entities erased by the previous ERASE command isdiscarded. OOPS cannot be used to restore them.AutoCAD allows backup step by step to an earlier point in an editing session, usingthe UNDO command. This stores all the sequences made by the user in the current drawingsession.
Computer Aided Draughting 409dharmd:\N-Design\Des21-1.pm5UNDO Command—this command allows to undo several commands at once. Thiscommand is used for correcting any errors made in the editing process. When a SAVE option isused, then the UNDO cannot do anything before that.Command: UNDOIf the response contains a number, that many number of preceding operations will beundone.REDO Command—if REDO is entered immediately after a command that undoessomething, it will undo the UNDO.Command: REDOAn UNDO after REDO will redo the original UNDO.OFFSET Command—this constructs an entity parallel to another entity at either aspecified distance or through a specified point.MIRROR Command—this allows to mirror the selected entities in the drawing. Theoriginal objects can be deleted (like a move)/retained (like a copy).MOVE Command—the move command is used to move one/more existing drawing entitiesfrom one location in the drawing to another.COPY Command—this is used to duplicate one or more existing drawing elements atanother location without erasing the original.21.8.2 Zoom CommandThis command acts like a Zoom lens on a camera. It is used to change the scale of the display.This can be used to magnify part of the drawing to any higher scale, for looking closely at somefine detail in the drawing. This is often quite useful during the construction stage. If zoomcloser, more details are visible but only a part of the drawing is seen, whereas if zoom out,larger portion of the drawing is seen but less details are visible. This command can be invokedfrom standard tool bar, from the pull down menu bar, from screen menu or from the commandarea by entering zoom.Command: ZOOMAll / Centre/ Dynamic/Left/Previous /Vmax/ Window/ <scale>:By choosing the option:All — complete drawing is seen in the drawing limits, even though a part of thedrawing lies outside the limits, earlier.Centre — this option permits to specify the desired centre point. By specifying theheight of window, the magnification can be increased/decreased.Left — it permits to specify the lower left corner of the display window instead ofthe centre.Dynamic — this displays the portion of the drawing specified already. Generally selectsany portion of the drawing.Extents — all the objects in the drawing are magnified to the largest extent possiblein display.Previous — the previous display extents are restored to the monitor, but the erasedobjects do not reappear.Window — by entering two opposite corners of a window, the area inside the windowis enlarged / reduced.
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dharmd:\N-Design\Des21-1.pm5Scale — by entering a display scale factor, the size of the object can be changed atwill in its appearance.21.8.3 Cross-hatching and Pattern FillingIt is common practice to fill an area with a pattern of some sort. The pattern can help differentiatebetween components, or it can signify the material composition of an object. This is accomplishedby HATCH command. Hatching generates line entities for the chosen pattern and adds them tothe drawing. AutoCAD normally groups these lines into a general block.HATCH Command—performs hatching. The pattern filling is illustrated in Fig. 21.11,by selecting appropriate choice in response to HATCH command.Command: HATCHPattern (? Name/ u, style) <default>😛attern name may be entered by choosing various available patterns which will bedisplayed by choosing u, by interaction, the angle, spacing between the lines and double hatcharea may be specified. By choosing style (Fig. 21.11), pattern filling may be achieved.abArea to be hatchedababNormal style(default)abOuter most styleababIgnore styleFig. 21.1121.8.4 Utility CommandsEND Command — this command exits the drawing editor and returns to the mainmenu and updates the drawing file.SAVE Command — this command saves the new/modified drawing and returns to themain menu. However, without exiting the drawing editor, if thechanges are to be periodically saved, it is desirable to use thiscommand. It protects the work from possible power failures, editingerrors, etc.Command: SAVEFile name <current>: return to save the current fileQUIT Command — this exits the drawing editor without saving the updated versionof the current drawing and returns to the main menu. The AutoCADchecksup with the user for one more confirmation to avoid theaccidental quitting since all the editing work done would be lost.TEXT Command — text may be added to a drawing by means of the TEXT command.Text entities can be drawn with a variety of character patterns orfonts and can be stretched, compressed or drawn in a verticalcolumn by applying a style to the font.
Computer Aided Draughting 411dharmd:\N-Design\Des21-1.pm5Command: TEXTStart point or Align/Centre/Fit/Middle/Right/Style:By choosing:Start point — Left justifies the text base line at the designated point.A (Align) — prompts for two end points of the base line and adjusts overall charactersize so that text just fits between these points.C (Centre) — asks for a point and centers the text base line at that point.F (Fit) — similar to ‘align’, but uses a specified fixed height.M (Middle) — like ‘centre’, but centers the text both horizontally and vertically at thedesignated middle point.R (Right) — right justifies the text base line at that point.S (Style) — asks for a new text style.Null reply — places the new text directly below the highlighted text.21.9 TYPES OF MODELLINGGeometric modelling provides a means ofrepresenting part geometry in graphicalrepresentation. This constitutes the mostimportant and complex part, in manysoftware packages. There are a variety ofmodelling methods available in the industryfor the variety of functions. They are:21.9.1 2D Wire FrameThis method consists of a range of 2D shapeswhich can be used to develop basically theoutline of a part, which in most of the casesis composed of lines and circles (Fig. 21.12), this is the easiest and most popular way to modelsimple parts. They are easy to understand.21.9.2 3D Wire FrameThis is similar to its 2D counter-part, except that it is drawn in 3 dimensions.This is used in low cost designing systems. The complete object is representedby a number of lines with their end point co-ordinates (x, y, z) and theirconnectivity relationships. It is difficult to understand the outside of the solid,represented by the wire frame model. Thus, the wire frame model is inadequatefor representing the more complex solids (Fig. 21.13).21.9.3 Surface ModellingIt is constructed essentially from surfaces such as planes, rotated curvedsurfaces and even very complex surfaces. These models are capable ofrepresenting the solid, from the manufacturing point of view. No informationregarding the interior of the solid model could be available.21.9.4 Solid ModellingThe best method for three dimensional solid construction is the solid modelling technique, oftencalled constructive solid geometry. In this, a number of 3 dimensional solids are provided asprimitives. From these solid primitives, the complex objects may be created by adding or subtractingFig. 21.12Fig. 21.13
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dharmd:\N-Design\Des21-1.pm5the primitives. A solid is a model that clearly identifies any point in space at either inside oroutside of the model. Each body is represented as a single object and not as a complex collectionof surfaces.21.10 VIEW POINTOne can view a drawing from any point in space. The VPOINT command permits to set theviewing point for the current view port. AutoCAD generates the drawing, projecting the entitiesso that they appear as one would see them from that point in space.Command: VPOINTRotate/<view point><current>.By choosingRotate: specify the view point in terms of two angles; one with respect to the x-axis (in x-yplane) and another from x-z plane.<view point>: one can enter x, y and z components of the desired view point (separated bycommas). A specification of “1, -1, 1” would produce top, right, front view. To generate perspectiveviews, one has to use DVIEW command.EXAMPLE: An upright cylinder at zero elevation with a radius 10 units and a height of40 units and enclosed in a square box (at zero elevation with a thickness of 15 units) can beproduced with the following sequence of commands:Command: ELEVNew current elevation <0>: ↵New current thickness <0>: ↵Command: CIRCLE (draw a circle with 10 units of radius)Command: ELEVNew current elevation <0>: ↵New current thickness <40>: 15 ↵Command: LINE (draw a square around circle)In the normal 2D (top) view, this would appear on the screen as shown in Fig. 21.14a. Witha view point (1, -1, 1) top, right side, front views appear as shown in Fig. 21.14b.(a)(b)Fig. 21.14
Computer Aided Draughting 413dharmd:\N-Design\Des21-1.pm521.10.1 V-point Co-ordinates View(s) Displayed0, 0, 1 top view0, – 1, 0 front view1, 0, 0 R side view– 1, 0, 0 L side view1, – 1,1 top, front, right side view– 1, – 1, 1 top, front, left side view21.11 VIEW PORTSThe rectangular portion of the graphics screen in which a drawing is displayed is called theview port. The screen may be divided into multiple view ports and individual controls can beexercised on each view port. One can have upto 4 view ports on screen at once (Fig. 21.15).AutoCAD Release 13 can display 16 view ports maximum on the computer monitor. Each viewport can display a different view of the drawing. Panning and zooming can be performed in eachview port independently. View ports are useful for checking the correctness of a design. Onecan edit the drawing in one view port and immediately see the results in all the view ports.Though several view ports can be displayed on the screen, one can work in only one of theview ports at a given time, known as current view port. This active view port is recognized by aheavy border. The cursor will be in the form of cross hairs when it is inside the current port andwill be an arrow outside it. Various views may be displayed in these view ports, such as: 3Dview, top view, side view, front view, etc.Command: VIEW PORTSSave/restore/delete/join/single/?/2/ <3>/4:Fig. 21.15By choosing:Save option — the active view port can be saved by giving a name upto 31 charactersand may be recalled at any time.Restore option — this restores any saved view port configuration. However, name ofthe configuration to restore, has to be supplied.
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dharmd:\N-Design\Des21-1.pm5Delete option — it deletes a saved view port configuration by supplying the particularname of the view port to be deleted.Join option — it allows two adjacent view ports into a single view port by selectingfirst the dominant view port and then selecting the other view port.The dominant view port will inherit the second view port by mergingboth.Single option — this allows to display a single view port, displaying the activeconfiguration.? option — it displays the number and co-ordinates of the current view portand the identification number and screen positions along with thenames and screen positions of the saved view port configurations.2 option — it allows the division of the current view port into equal parts, eitherhorizontally or vertically, based on the choice.3 option — it permits the division of the current view port into three ports.4 option — it creates 4 windows of equal size.21.12 CREATION OF 3D PRIMITIVESFrom the basic 3D primitives more complex solids can be built. A few such simple solids areshown in Fig. 21.16.(a) (b) ©Fig. 21.1621.12.1 To Draw a CylinderCylinder offers several methods of drawing a 3D solid cylinder. The default is to choose a centrepoint, then pick or enter the diameter/radius and height.Command: CYLINDER1. Elliptical / <centre point> <0, 0, 0>: ↵ or pick a centre point2. Diameter / <radius>: provide a diameter or radius by picking or entering3. Centre of other end / <height>: pick a point or enter a valueOptions:Centre — allows to create a cylinder with a circular base.Elliptical — allows to create a cylinder with an elliptical base.Centre of other end — allows to specify top end of the cylinder.Height — allows to specify the height of the cylinder.
Computer Aided Draughting 415dharmd:\N-Design\Des21-1.pm521.12.2 To Draw ConeCone offers several methods for drawing a 3D solid cone. The default is to choose a centre point,then pick or enter the diameter/radius and apex.Command: CONE1. Elliptical /<centre point> <0, 0, 0): pick a centre point or enter E2. Diameter / <radius>: provide a diameter or radius3. Apex /<height>: provide the apex or heightOptions:Centre — allows to create a cone with a circular base.Elliptical — allows to create a cone with an elliptical base.Centre of other end — allows to specify top end of the cone.Height — allows to specify the height of the cone.21.12.3 To Draw a BoxThe box command creates a 3D solid box.Command: BOX1. Centre/ <corner of box> <0, 0, 0>: pick up the first corner point for the box2. Cube/length/ <other corner>: pick up a second corner point or enter a value3. <Height>: provide the box height by picking two points or entering a valueOptions:Centre — allows to create a 3D box using a specified centre point.Cube — allows to create a 3D box with all sides equal.Length — allows to enter values for length, width and height.21.13 CREATION OF COMPOSITE SOLIDSComplex solids can be created from both solid primitives and swept solids. Boolean operationscan be used to create composite solids from two or more solids. Solid modelling is a built-infacility with AutoCAD 14, which provides for region and solid modelling. Region models are twodimensional closed areas consisting of lines, polylines, arcs, circles and ellipses. From these,mass properties and surface areas can be assessed. Solid models are true shape 3D objects.The region command allows creating 2D enclosed areas from existing overlapping closedshapes (loops).21.13.1 To Create RegionsCommand: REGION1. Select objects: select objects to be combined into a region2. Press: ↵A composite region may be created by subtracting, combining or finding the intersectionof regions.To create composite regions (Fig. 21.17a, b):Command: Union, Subtract and Intersect1. Select objects: select the regions to be combined into a composite region2. Press ↵ to end the command
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dharmd:\N-Design\Des21-1.pm5Objects may be selected in any order to unite them with the union command and when itis required to subtract one region from the other, first select the region from which it is requiredto subtract. Condition: these regions exist overlapping, earlier to the operations.(a) Union (b) SubtractFig. 21.1721.13.2 Solid ModellingA composite solid can be created from both solid primitives and swept solids or by extruding a2D object, Boolean operations can be used.Options:Union — allows combining the volume of two or more solids into one. Select theobjects to join and AutoCAD creates a single composite object.Subtract — allows to remove the common area shared by two sets of solids. One mustfirst select the solid from which to subtract and then the solid (s) whichare to be subtracted.Intersect — allows creating a composite solid that contains only the common volumeof two or more overlapping solids.21.13.3 Mass PropertyMass prop calculates and displays the mass properties of 2D and 3D objects. For solids, it providesvolumetric information such as mass, volume, centre of gravity, principal axes and moments ofinertia.Command: MASS PROP1. Select objects: pick the solid model (s) to be analysed. This will display all the propertiesof the object(s) on the screen2. Write to a file <N>: if one wants the information written to a file, type Y and providea file name.For regions, the mass properties displayed are area, perimeter, centroid, moment of inertia,product of inertia and radius of gyration.21.14 SECTIONAL VIEWWhen a section plane cuts a part of the solid and the remaining part of the solid is projected,that view is known as sectional view. Sectional views are chosen to reveal the inner details (hidden).One may use full section, half section or off-set section to reveal the hidden details of the object
Computer Aided Draughting 417dharmd:\N-Design\Des21-1.pm5150°30°TopLeftRight90°(refer Chapter 2 and section 2.6) and the sectioned zone in any view is shown by cross-hatchedlines. Thin lines represent the cross-hatched lines. It is possible to change the hatching lines.SOL VIEW uses orthographic projections with floating paper space view ports to layoutmulti-and sectional view drawings of 3D solids.Command: SOLVIEWUCS/ ORTHO/ AUXILIARY / SECTION/ <EXIT>:By choosing the option section-use the original view port and specify two points at theprompts to define the section plane. Then define the viewing side by specifying a point on oneside of the cutting plane, for the next prompt.21.15 ISOMETRIC DRAWINGThe command “isoplane” permits to switch the cursor orientation between the left, top andright isometric planes when the snap mode is set to the isometric style.Command: ISOPLANELeft /top/ right/ <toggle>: enter the choice to move to right, isoplane left or isoplane top.By pressing ctrl and E keys simultaneously, toggle takes place between the isometric planes.21.15.1 Setting Isometric Grid and SnapUse snap command for choosing between thestandard orthogonal snap style and isometric snapstyle-by selecting style. The grid points are arrangedalong 30°, 90° and 150° lines. The distance betweenthe grid lines is determined by the vertical spacing.To draw the cube in isometric view(Fig. 21.18):Command: isoplane-by choosing top, left andright planes, one at a time, the squares are drawn tocomplete the cube. Isometric circles are drawn usingthe command ellipse and selecting iso-circles option.This is possible when isometric snap is on.21.16 BASIC DIMENSIONINGIn many applications, a drawing should contain annotations showing lengths or distances orangles between objects to convey the desired information. Dimensioning is the process of addingthese annotations to a drawing. AutoCAD provides four basic types of dimensioning; linear,angular, diameter and radius.DIM and DIMI Commands—DIMI command allows executing one dimensioning commandand then returns to the normal command mode. If several dimensioning commands are to beexecuted, DIM command should be used. In this mode, the normal set of AutoCAD commandsis replaced by a special set of dimensioning commands. To end the process of dimensioning,EXIT command has to be used.The dimensioning commands can be grouped into six categories:1. Linear — is done with a horizontal, vertical, aligned and rotated command.However, rotated command requires specifying the dimension lineangle explicitly.Fig. 21.18
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dharmd:\N-Design\Des21-1.pm580Horizontal60 20Continuing60Vertical8550Base line dimensionDiameterLeader dimensionf3045°Angular75Aligned dimensionRadiusR4550Fig. 21.192. Angular — is used to dimension angles. Here, one has to select two non-parallellines to introduce the angular dimension.3. Diameter — this can be invoked for dimensioning arcs and circles.4. Radius — it is almost identical to diameter dimensioning, except that only aradius line is drawn. This line has only one arrow.5. Associative — used to make various changes to associative dimension entities.6. Dimensioning utility commands— to draw a centre line or centre mark for a circle/arc, this command isused.AutoCAD generally uses same type of dimensions and dimension label components as standarddraughting. Figure 21.19 gives examples of types of dimensions possible: linear, angular,diametric, radial and aligned. A number of variables such as extension lines, text location,tolerance specifications, arrow styles and sizes, etc., actually control the way in which thedimensions may appear in the drawings.21.16.1 Dimensioning FundamentalsThe student is already exposed to some definitions of fundamentals. However, the following arespecific for AutoCAD: (i) Base line dimension-a series of dimension lines, all starting at thesame extension line, that measure successive linear distances. (ii) Continuing dimension—aseries of dimension lines that follow one another along successive linear distances.21.16.2 Dimensioning MethodsThe procedure to be followed for dimensioning in AutoCAD is as follows:
Computer Aided Draughting 419dharmd:\N-Design\Des21-1.pm51. Set-up the basic parameters for dimensioning. They are,(a) arrow head size,(b) arrow head type,© extension line offset, and(d) placement of dimension text.2. Identify what to measure–pick the end points, lines, arcs or circles or other points ofexisting drawing entities using OSNAP if neccessary.3. Specify where the dimension line and text are to be located.4. Approve AutoCAD’s measurements or can type one’s own text.21.16.3 Linear DimensionsCommand: DIMDim: hor/ver/ali/cont/ang/diam/rad/leaderChose any one based on the requirement (Fig. 21.19)First extension line origin or return to select: ↵Select line, arc, or circle: pickDimension line location: pickDimension text <value>: ↵Dim: exit21.16.4 Continuing Linear DimensionsOften a series of related dimensions must be drawn, sometimes several dimensions are measuredfrom the same base line; other times one long dimension is broken into shorter segments thatadd upto the total measurement. The base line and continue commands are provided to simplifythese operations. Draw the first dimension, using horizontal, vertical, aligned or rotatedcommands. Then enter base line or continue. AutoCAD proceeds directly to the “second extensionline origin” prompt, and then asks for the dimension text. The dimension line is placed at thesame angle as the previous dimension.Fig. 21.20When the base line command is used, AutoCAD offsets each new dimension line by anamount to avoid overlaying the previous dimension line. The first dimension line is extended
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dharmd:\N-Design\Des21-1.pm5accordingly. Dimension line off-setting can also occur with the continue command if either thenew or previous dimension has its arrows outside the extension lines. In Fig. 21.20, the horizontal;dimensions are drawn using continue command and the vertical dimensions are drawn usingbase line command.21.16.5 Example for DimensioningFor the example considered, (Fig. 21.21), the method of dimensioning with the associated dialoguewith AutoCAD is given below, in the same serial order:1. Command: dim linearFirst extension line origin or return to select:—int ofSecond extension line origin:—cen ofDimension line location (text/angle/horizontal/vertical/rotated): pickDimension text <130>:2. Dim: baseSecond extension line origin: — cen ofdimension text <260>:3. Command: dim linearFirst extension line origin or return to select:— int ofSecond extension line origin: — cen ofDimension line location (text/angle/horizontal/vertical/rotated): pickDimension text <25>:4. Dim: verticalFirst extension line origin or return to select: — int ofSecond extension line origin: —cen ofDimension line location (text/angle/horizontal/vertical/rotated): pickDimension text <20>:5. Dim: baseSecond extension line origin: — cen ofDimension text <75>:6. Dim: baseSecond extension line origin: — int ofDimension text <150>:7. Dim: HorizontalFirst extension line origin or return to select: pickSecond extension line origin: pickDimension line location (text/angle/horizontal/vertical/rotated): pickDimension text <120>:8. Dim: VerticalFirst extension line origin or return to select: pickSecond extension line origin: pickDimension line location (text/angle/horizontal/vertical/rotated): pickDimension text <80>:
Computer Aided Draughting 421dharmd:\N-Design\Des21-1.pm56150f20910712011f60108801130226032510204755Fig. 21.219. Dim: leaderLeader start: pickTo point: pickTo point: ↵Dimension text <20>: φ20Dim: exit10. Command: DimSelect arc or circle: pickSelect arc or circle; pickSelect arc or circle: pickSelect arc or circle: ↵11. Dim: diameterSelect arc or circle: pickDimension text <60>: φ6021.17 POLYLINE (PLINE)Polyline is basically a composite curve which is a combination of linear and arc segments inAutoCAD. The other property that can be varied is the thickness of the line drawn. Specialproperties of the polyline are🙁a) All the connected segments are treated as single entity.(b) Width of line of any or all segments can be varied.© It can also be a closed curve.(d) Line type can be varied as required along various segments of the line.
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