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Chapter 8 Multiview Drawings - mhhe.com

As lines, so loves oblique, may wellThemselves in every angle greet;But ours, so truly parallel,Though infinite, can never Marvell375 ChapterMultiview Drawings8 OBJECTIVESA fter completing this Chapter , you will be able to:1. Explain orthographic and Multiview Identify frontal, horizontal, and profile Identify the six principal views and the three Apply standard line practices to Multiview Create a Multiview drawing using hand tools Identify normal, inclined, and oblique planes inmultiview Represent lines, curves, surfaces, holes, fillets,rounds, chamfers, runouts, and ellipses in Apply visualization by solids and surfaces tomultiview Explain the importance of Multiview Identify limiting elements, hidden features, andintersections of two planes in Multiview 8 introduces the theory, techniques, and standardsof Multiview Drawings , which are a standard method forrepresenting engineering designs.

object is oriented such that only two of its dimensions are shown. (Figure 8.7) As the parallel lines of sight pierce the projection plane, the features of the part are outlined. Multiview drawings employ multiview projection techniques. In multiview drawings, generally three views of an object are drawn, and the features and dimensions

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Transcription of Chapter 8 Multiview Drawings - mhhe.com

1 As lines, so loves oblique, may wellThemselves in every angle greet;But ours, so truly parallel,Though infinite, can never Marvell375 ChapterMultiview Drawings8 OBJECTIVESA fter completing this Chapter , you will be able to:1. Explain orthographic and Multiview Identify frontal, horizontal, and profile Identify the six principal views and the three Apply standard line practices to Multiview Create a Multiview drawing using hand tools Identify normal, inclined, and oblique planes inmultiview Represent lines, curves, surfaces, holes, fillets,rounds, chamfers, runouts, and ellipses in Apply visualization by solids and surfaces tomultiview Explain the importance of Multiview Identify limiting elements, hidden features, andintersections of two planes in Multiview 8 introduces the theory, techniques, and standardsof Multiview Drawings , which are a standard method forrepresenting engineering designs.

2 The Chapter describeshow to create one-, two-, and three-view Drawings withtraditional tools and CAD. Also described are standardpractices for representing edges, curves, holes, tangencies,and fillets and rounds. The foundation of Multiview draw-ings is orthographic projection, based on parallel lines ofsight and mutually perpendicular views. PROJECTION THEORYE ngineering and technical graphics are dependent on pro-jection methods. The two projection methods primarilyused are perspective and parallel. (Figure ) Bothmethods are based on projection theory, which has takenmany years to evolve the rules used theory comprises the principles used torepresent graphically 3-D objects and structures on 2-DProjectionsPerspective or CentralProjectionsParallel ProjectionsThe Attributes of Each Projection MethodProjection MethodLinear Perspective-One-Point-Two-Point-Three-Po intOblique Projection-Cavalier-Cabinet-GeneralOrtho graphic ProjectionAxonometric-Isometric-Dimetric -TrimetricMultiview Projection-Third Angle-First AngleLines ofSightOne principalplane parallelto plane ofprojectionApplication(preferrred)Conve rging;inclined toplane ofprojectionParallel;normal toplane ofprojectionParallel;inclined toplane ofprojectionParallel.

3 Normal toplane ofprojectionSometimesAlwaysNeverFor allprincipalviewsSingle viewpictorialSingle viewpictorialSingle viewpictorialMultiviewdrawingsOrthograph icProjectionsOne-PointPerspectiveThree-p ointPerspectiveTwo-PointPerspectiveCabin etProjectionCavalierProjectionGeneralPro jectionIsometricoq = or = oga =b =cqgabcroqgrabcoqrgabcoDimetricTrimetric oq or oga b cMultiviewProjectionsAxonometricProjecti onsFirst-angle projectionThird-angle projectionRSFTTFRSTFRSFTRSL inearPerspectivesAerialPerspectivesObliq ueProjectionsAerial PerspectiveObject features appearless focused at a distanceDepthVariesFullDepthHalfDepthoq = or oga = b cFigure techniquesdeveloped along two lines:parallel and 8 Multiview Drawings377media. An example of one of the methods developed toaccomplish this task is shown in Figure , which is apictorial drawing with shades and shadows to give theimpression of three projection theory is based on two variables: line ofsight and plane of projection.

4 These variables are de-scribed briefly in the following Line of Sight (LOS)Drawing more than one face of an object by rotating theobject relative to your line of sighthelps in understandingthe 3-D form. (Figure ) A line of sight (LOS) is animaginary ray of light between an observer s eye and anobject. In perspective projection, all lines of sight start ata single point (Figure ); in parallel projection, all linesof sight are parallel (Figure ). Plane of ProjectionA plane of projection ( , an image or picture plane) isan imaginary flat plane upon which the image created bythe lines of sight is projected. The image is produced byconnecting the points where the lines of sight pierce theprojection plane. (See Figure ) In effect, the 3-D ob-ject is transformed into a 2-D representation (also calleda projection). The paper or computer screen on which asketch or drawing is created is a plane of IllustrationThis is a computer-generated pictorial illustration with shadesand shadows.

5 These rendering techniques help enhance the 3-Dquality of the image. (Courtesy of SDRC.)ORTHOGRAPHICREVOLVEDTIPPED FORWARDO rthographicRevolvedTipped forwardPaper(Plane of projection)Parallel lines of sightFigure ViewpointChanging the position of the object relative to the line of sight creates different views of the same Parallel versus Perspective ProjectionIf the distance from the observer to the object is infinite(or essentially so), then the projectors( , projectionlines) are parallel and the drawing is classified as a paral-lel projection. (See Figure ) Parallel projection378 PART 2 Fundamentals of Technical Graphicsrequires that the object be positioned at infinity andviewed from multiple points on an imaginary line paral-lel to the object . If the distance from the observer to theobject is finite, then the projectors are not parallel and thedrawing is classified as a perspective projection.

6 (SeePicture plane(paper or computer screen)Nonparallel lines of sightradiating from a pointObserver (Station point)One viewpointView of object projected ontopicture planeFigure ProjectionRadiating lines of sight produce a perspective lines of sightObserver (Station point)Infinite viewpointPicture plane(paper or computer screen)View of object projected ontopicture planeFigure ProjectionParallel lines of sight produce a parallel 8 Multiview Drawings379 Figure ) Perspective projection requires that the ob-ject be positioned at a finite distance and viewed from asingle point (station point).Perspective projections mimic what the human eyesees; however, perspective Drawings are difficult to cre-ate. Parallel projections are less realistic, but they areeasier to draw. This Chapter will focus on parallel projec-tion. Perspective Drawings are covered in Chapter projection is a parallel projectiontechnique in which the plane of projection is positionedbetween the observer and the object and is perpendicularto the parallel lines of sight.

7 The orthographic projectiontechnique can produce either pictorial Drawings thatshow all three dimensions of an object in one view ormultiviews that show only two dimensions of an objectin a single view. (Figure ) PROJECTION PLANESM ultiview projection is an orthographic projection forwhich the object is behind the plane of projection, and theobject is oriented such that only two of its dimensions areshown. (Figure ) As the parallel lines of sight piercethe projection plane, the features of the part are Drawings employ Multiview projectiontechniques. In Multiview Drawings , generally three viewsof an object are drawn, and the features and dimensionsin each view accurately represent those of the view is a 2-D flat image, as shown in Figure views are defined according to the positions of theplanes of projection with respect to the Frontal Plane of ProjectionThefront viewof an object shows the widthand heightdimensions.

8 The views in Figures and are frontviews. The frontal plane of projection is the plane ontowhich the front view of a Multiview drawing is ProjectionParallel projection techniques can be used to create multiviewor pictorial ofprojection(frontal)Projectors perpendicular toplane(A)Plane ofprojection(frontal)Lines of sightperpendicular to planeof projectionObject s depth is notrepresentedFrontview(B)DepthFigure ProjectionOrthographic projection is used to create this front Multiview drawing by projecting details onto a projection plane that is parallel tothe view of the object selected as the 2 Fundamentals of Technical GraphicsIndustry ApplicationCAD and Stereolithography Speed Solenoid DesignSource: CAD and Stereolithography Speed Solenoid Design, Machine Design, August 13, 1993, p. 80. Photos courtesy of Thomas J. Pellegatto, Senior DesignEngineer, Peter Paul Electronics Co. Inc., New Britain, CT 06050 Peter Paul Electronics faced the need to quickly re-design a humidifier solenoid valve, Senior Design Engi-neer Thomas J.

9 Pellegatto naturally turned his CAD-KEY-based system loose on the physical parameters of thenew valve. But that wasn t enough. The design requiredlower-cost manufacturing technology as well as dimen-sional and mechanical design valves from the company feature an all-steelsleeve, consisting of a flange nut, tube, and end stop, allof which are staked together for welding. A weld bead se-cures the end stop to the tube at the top edge and joinsthe tube and threaded portion of the flange nut at the bot-tom. Alignment of these components becomes critical be-The three components created in plastic include theovermolded valve housing with integral bracket (red), thebobbin on which the coil is wound, and the valve body withwhich the solenoid valve is connected (blue).Redesign and simplification of the solenoid valve coil andsleeve assembly (left) is easily compared with the coil-on-bobbin assembly.

10 The extended and molded one-piecebobbin eliminates the use of two machined parts, two welds,and one quality operation while providing an improvedmagnetic circuit, reduced weight, and lower the sleeve sits inside the coil, which is the heart ofthe solenoid valve. In addition, a plunger that causes airor fluid to flow in the valve rises inside the to Pellegatto, the simplest method for reducing cost and complexity of the critical sleeve assembly was to use the coil s bobbin to replace thesleeve and house the plunger. Working directly with engi-neers at DuPont, designers selected a thermoplasticnamed Rynite to eliminate misalignment and the need forwelding the new assembly. The CAD system fed PeterPaul s internal model shop with the data to develop bob-bin prototypes from the thermoplastic. In addition, de-signers decided to mold the formerly metallic mountingbracket as part of the plastic designs were finalized, Pellegatto sent the CADfile to a local stereolithography shop, which built demon-stration models using a 3D Systems unit.