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# Engineering Drawing

###### Engineering Drawing 21
Engineering Drawing Traditional Drawing Tools DRAWING TOOLS DRAWING TOOLS 1. TSquare 2. Triangles DRAWING TOOLS HB for thick line 2H for thin line 3. Adhesive Tape 4. Pencils DRAWING TOOLS 5. Sandpaper 6. Compass DRAWING TOOLS 7. Pencil Eraser 8. Erasing Shield DRAWING TOOLS 9. Circle Template 10. Tissue paper DRAWING TOOLS 11. Sharpener 12. Clean paper Freehand Sketching Straight Line 1. Hold the pencil naturally. 2. Spot the beginning and end points. 3. Swing the pencil back and forth between the points, barely touching the paper until the direction is clearly established. 4. Draw the line firmly with a free and easy wristandarm motion Horizontal line Vertical line Nearly vertical inclined line Nearly horizontal inclined line Small Circle Method 1 : Starting with a square 1. Lightly sketching the square and marking the midpoints. 2. Draw light diagonals and mark the estimated radius. 3. Draw the circle through the eight points. Step 2 Step 3 Step 1 Small Circle Method 2 : Starting with center line 1. Lightly draw a center line. 2. Add light radial lines and mark the estimated radius. 3. Sketch the full circle. Step 2 Step 3 Step 1 Arc Method 1 : Starting with a square Method 2 : Starting with a center line Basic Strokes Straight Slanted Horizontal Curved Examples : Application of basic stroke 4 5 1 “I” letter “A” letter “B” letter 1 2 1 6 3 3 2 Uppercase letters Numerals Suggested Strokes Sequence Straight line letters Curved line letters Curved line letters Numerals Lowercase letters Suggested Strokes Sequence The text’ s body height is about 2/3 the height of a capital letter. Example : Good and Poor Lettering GOOD Not uniform in style. Not uniform in height. Not uniformly vertical or inclined. Not uniform in thickness of stroke. Area between letters not uniform. Area between words not uniform. Sentence Composition Leave the space between words equal to the space requires for writing a letter “O”. Example ALLO DIMEN SIONSO IN AREO MILLIMETERS UNLESS O SPECIFIED. OTHERWISEO GRAPHICS LANGUAGE Effectiveness of Graphics Language 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. You can easily understand that … The word languages are inadequate for describing the size, shape and features completely as well as concisely. Composition of Graphic Language Graphic language use lines to represent the surfaces, edges and contours of objects. The language is known as “drawing” or “drafting” . A drawing can be done using freehand, instruments or computer methods. Freehand drawing The lines are sketched without using instruments other than pencils and erasers. Example Instrument drawing Instruments are used to draw straight lines, circles, and curves concisely and accurately. Thus, the drawings are usually made to scale. Example Computer drawing The drawings are usually made by commercial software such as AutoCAD, solid works etc. Example Architectural Graphics Elements Drawing comprises of graphics language and word language. Graphics language Describe a shape (mainly). Word language Describe size, location and specification of the object. Basic Knowledge for Drafting Word Graphics language language Geometric Line Projection Lettering construction types method PROJECTION METHOD PROJECTION METHOD Perspective Parallel Oblique Orthographic Axonometric Multiview PROJECTION THEORY The projection theory is used to graphically represent 3D objects on 2D media (paper, computer screen). The projection theory is based on two variables: 1) Line of sight 2) Plane of projection (image plane or picture plane) Line of sight is an imaginary ray of light between an observer’s eye and an object. parallel converge and There are 2 types of LOS : Parallel projection Perspective projection Line of sight Line of sight 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 projection Perspective projection Plane of projection Plane of projection Disadvantage of Perspective Projection 1) It is difficult to create. 2) It does not reveal exact shape and size. Width is distorted Orthographic Projection MEANING Orthographic projection is a parallel projection technique in which the parallel lines of sight are perpendicular to the projection plane Object views from top 1 2 1 5 2 3 4 5 3 4 Projection plane ORTHOGRAPHIC VIEW Orthographic view depends on relative position of the object to the line of sight. Rotate Two dimensions of an object is shown. Tilt More than one view is needed to represent the object. Multiview drawing Three dimensions of an object is shown. Axonometric drawing ORTHOGRAPHIC VIEW NOTES 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. Axonometric (Isometric) Drawing Advantage Easy to understand Disadvantage Shape and angle distortion Example Distortions of shape and size in isometric drawing Circular hole becomes ellipse. Right angle becomes obtuse angle. Types of Axonometrics Multiview Drawing Advantage It represents accurate shape and size. Disadvantage Require practice in writing and reading. Example Multiviews drawing (2view drawing) The Glass Box Approach Orthographic Projection Opening the Box Final Views Six Orthographic Views Laying Out All Six Views Three Primary Views Construction of Views First and Third Angle Projections Thirdangle Projection Firstangle Projection • First Angle – International • Third Angle – U.S. Basic Line Types Name according Types of Lines Appearance to application Continuous thick line Visible line Dimension line Continuous thin line Extension line Leader line Dash thick line Hidden line Chain thin line Center line Meaning of Lines Visible lines represent features that can be seen in the current view Hidden lines represent features that can not be seen in the current view Center line represents symmetry, path of motion, centers of circles, axis of axisymmetrical parts Dimension and Extension lines indicate the sizes and location of features on a drawing Example : Line conventions in engineering drawing Good practice Exercise • Complete three orthographic views of the object shown on the next slide. • Include visible, hidden, and center lines where appropriate. • You will be given 7 minutes. Object for exercise Solution Drawing Standard Introduction Standards are set of rules that govern how technical drawings are represented. Drawing standards are used so that drawings convey the same meaning to everyone who reads them. Standard Code Full name Country Code USA American National Standard Institute ANSI Japanese Industrial Standard Japan JIS British Standard UK BS Australian Standard Australia AS Deutsches Institut für Normung Germany DIN International Standards Organization ISO Partial List of Drawing Standards Contents Code number JIS Z 8311 Sizes and Format of Drawings JIS Z 8312 Line Conventions JIS Z 8313 Lettering JIS Z 8314 Scales JIS Z 8315 Projection methods JIS Z 8316 Presentation of Views and Sections JIS Z 8317 Dimensioning Drawing Sheet A4 Trimmed paper of a size A0 A4. A3 Standard sheet size A2 (JIS) A4 210 x 297 A1 A3 297 x 420 A2 420 x 594 A1 594 x 841 A0 841 x 1189 (Dimensions in millimeters) A0 Orientation of drawing sheet 1. Type X (A0A4) 2. Type Y (A4 only) d d c Drawing Drawing space Border Title block space lines Title block Sheet size c (min) d (min) A4 10 25 A3 10 25 A2 10 25 A1 20 25 A0 20 25 c c Drawing Scales Length, size Scale is the ratio of the linear dimension of an element of an object shown in the drawing to the real linear dimension of the same element of the object. Size in drawing Actual size : Drawing Scales Designation of a scale consists of the word “SCALE” followed by the indication of its ratio, as follow SCALE 1:1 for full size SCALE X:1 for enlargement scales SCALE 1:X for reduction scales
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15-07-2017

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