Introduction

Lecture 5Dr. Khaled BakroEngineering DrawingIntroduction to Engineering and Profession Ethics

PART 4 ENGINEERING GRAPHICAL COMMUNICATIONIn this chapter: we will explain 16- ENGINEERING DRAWINGS AND SYMBOLSProjection methods

Orthographic projection

Graphics language

Engineering drawing

GRAPHICS LANGUAGE

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1. Try to write a description of this object.2. Test your written description by having someone attempt to make a sketch from your description.Effectiveness of Graphics LanguageThe word languages are inadequate for describing the size, shape and features completely as well as concisely.You can easily understand that

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Graphic language in engineering application uselines to represent the surfaces, edges and contoursof objects.A drawing can be done using freehand, instruments or computer methods.

Composition of Graphic LanguageThe language is known as drawing or drafting .

Freehand drawing The lines are sketched without using instruments other than pencils and erasers.Example

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Instrument drawing Instruments are used to draw straight lines, circles, and curves concisely and accurately. Thus, the drawings are usually made to scale.Example

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Why and What?Why do we use sketching?To make a quick, graphic representation of an idea that can be easily communicated. How do we represent objects so that others will understand all essential features?Use a graphics language. It has its own rules and conventions so everybody can communicate.

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How?How do we represent a real object (3D) on paper (2D)?The graphics language has conventions for different types of 2D views.How do we develop the skill to read representations made by other people? Understand the language and practice using it.

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Computer drawing The drawings are usually made by commercial software such as AutoCAD, solid works etc.Example

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Engineering Drawing

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Engineering Drawing DefinitionA languagea graphical language that communicates ideas and information from one mind to another.

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Engineering Drawing FunctionInformation deliveryPreservation, archiving, use of informationWays of thinking in the preparation of information

Some Examples of Engineering Drawing

Some Examples of Engineering Drawing

Some Examples of Engineering Drawing

Some Examples of Engineering Drawing

Some Examples of Engineering Drawing

Engineering Drawing

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Elements of Engineering DrawingEngineering drawing are made up of graphics languageand word language.

GraphicslanguageDescribe a shape(mainly).WordlanguageDescribe size, location andspecification of the object.

Basic Knowledge for DraftingGraphicslanguageWordlanguageLinetypesGeometricconstructionLetteringProjectionmethod

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Knowledge and Skills RequireGraphicslanguageWordlanguageDimensions & NotesVisualization is the ability to mentally picture things that do not exists.Visualization

Using line types

Geometricconstruction

Projectionmethod

Engineering Drawing

PROJECTION METHOD

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PROJECTION METHOD

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PROJECTION METHOD

Perspective

Oblique

Orthographic

Axonometric

Multiview

Parallel

PROJECTION THEORYThe projection theory is based on two variables:1) Line of sight2) Plane of projection (image plane or picture plane)

The projection theory is used to graphically represent3-D objects on 2-D media (paper, computer screen).

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Line of sight (LOS) is an imaginary ray of light between an observers eye and an object.

Line of sightParallel projection

Line of sightPerspective projectionThere are 2 types of LOS :

parallelconvergeand

Plane of projection is an imaginary flat plane which the image is created.The image is produced by connecting the points where the LOS pierce the projection plane.

Parallel projectionPerspective projection

Plane of projection

Plane of projection

Disadvantage ofPerspective ProjectionPerspective projection is not used by engineer for manu-facturing of parts, because

1) It is difficult to create.2) It does not reveal exact shape and size.

Width is distorted

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Orthographic Projection

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Orthographic projection is a parallel projection techniquein which the parallel lines of sight are perpendicular to theprojection planeMEANING

Object views from top

Projection plane

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1

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ORTHOGRAPHIC VIEWOrthographic view depends on relative position of the objectto the line of sight.

Two dimensions of anobject is shown.Three dimensions of an object is shown.

RotateTiltMore than one view is neededto represent the object.

Multiview drawing

Axonometric drawing

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Orthographic Projection

Orthographic projection technique can produce either 1. Multiview drawing that each view show an object in two dimensions.

2. Axonometric drawing that show all three dimensions of an object in one view.

Both drawing types are used in technical drawing for communication.

NOTESORTHOGRAPHIC VIEW

Axonometric (Isometric) Drawing Easy to understand

Right angle becomes obtuse angle.Circular hole becomes ellipse.

Distortions of shape and size in isometric drawingAdvantageDisadvantageShape and angle distortion Example

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Multiview DrawingIt represents accurate shape and size.AdvantageDisadvantageRequire practice in writing and reading.

Multiviews drawing (2-view drawing)Example

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SUMMARYYou should have a good understanding of the importance of engineering drawings in conveying information to other engineers.You should understand what is meant by orthographic views, isometric drawing, and solid modeling.You should understand the basic rules required for an engineering drawing, including showing dimensions, specifying material size, and indicating finished surfaces.You should know when to use isometric views and sectional views.

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