Dept. of Mechanical and Automation Engineering 2017/4/20 ENGG1100 Introduction to Engineering Design Introduction to Engineering Drawing Professor Yunhui Liu Dept. of Mechanical and Automation Engineering Spring, 2014 asrgwELFGWLKEFLKWEFLKN MAE Dept., The Chinese University of Hong Kong 1

What is Engineering Drawing? An engineering drawing is a type of technical drawing used to fully and clearly define requirements for engineered items (from en.wikipedia.org) a formal and precise way (graphic language) for communicating information about the shape and size of physical objects. a mean for specifying the precision of physical objects. Important as it is a legal document, i.e., if the drawings are wrong, it is the fault of the engineers! MAE Dept., The Chinese University of Hong Kong 2

Why ? Effectiveness of Engineering Drawing 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. MAE, CUHK From Lec. Bhuiyan Shameem Mahmood

From Lec. Bhuiyan Shameem Mahmood Graphic Language Graphic language in “engineering applications” uses 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. From Lec. Bhuiyan Shameem Mahmood

Bhuiyan Shameem Mahmood Ebna Hai Freehand drawing The lines are sketched without using instruments other than pencils and erasers. Example From Lec. Bhuiyan Shameem Mahmood AE Dept. MIST

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

From Lec. Bhuiyan Shameem Mahmood Computer drawing The drawings are usually made by commercial software such as AutoCAD, SolidWorks etc. Example From Lec. Bhuiyan Shameem Mahmood

Elements of Engineering Drawing 2017/4/20 Elements of Engineering Drawing Engineering drawing is made up of graphics language and word language. Graphics language Describe a shape (mainly by projected views). Projections of the object Word language Describe size, location and specification of the object. From Lec. Bhuiyan Shameem Mahmood

PROJECTION METHOD Perspective Parallel Oblique Orthographic Axonometric Multiview From Lec. Bhuiyan Shameem Mahmood

Bhuiyan Shameem Mahmood Ebna Hai PROJECTION THEORY The projection theory is used to graphically represent 3-D objects on 2-D 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) From Lec. Bhuiyan Shameem Mahmood AE Dept. MIST

Perspective projection From Lec. Bhuiyan Shameem Mahmood Line of sight is an imaginary ray of light between an observer’s eye and an object. There are 2 types of LOS : parallel and converge Parallel projection Perspective projection Line of sight Line of sight From Lec. Bhuiyan Shameem Mahmood

Perspective projection From Lec. Bhuiyan Shameem Mahmood 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 From Lec. Bhuiyan Shameem Mahmood

Orthographic Projection 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 From Lec. Bhuiyan Shameem Mahmood

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 From Lec. Bhuiyan Shameem Mahmood

Multiview Projections 2017/4/20 Multiview Projections Project an object from six principal directions (front, back, top, bottom, right, left) (From lecture notes of course MAEG2010) MAE Dept., The Chinese University of Hong Kong 16

Auxiliary Views Used to show true dimensions of an inclined plane. From Lec. Bhuiyan Shameem Mahmood

Isometric Drawing Represent 3-D objects by a 2D view in the projection in which the coordinate axes appear equally foreshortened. It is easy to understand the 3-D shape However, the projection causes shape and angle distortions Circular hole becomes ellipse. Right angle becomes obtuse angle. MAE Dept., The Chinese University of Hong Kong 18

Drawing Standards 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. From Lec. Bhuiyan Shameem Mahmood

Drawing Standards Standards on Sizes and Format of Drawings Lines Scales Projection methods Presentation of view and sections Lettering Dimensioning … MAE Dept., The Chinese University of Hong Kong 20

Standard on Placement of Projected Views: First Angle Projection ISO standard Used in Europe, etc. Top view Back view Bottom view Right view Left view Front view From mytvmoments.com Directly project images along the line of sight Front view is put at the middle Top view is put at the bottom Right view is put on the left (En.wikipedia.com)

Standard on Placement of Views: Third Angle Projection The positions of the viewpoint and location of the projection view are the same Right side view is located at right Left side view is located at left … Mainly used in US MAE Dept., The Chinese University of Hong Kong 22

(Dimensions in millimeters) Drawing Sheet A4 Trimmed paper of a size A0 ~ A4. A3 Standard sheet size A4 210 x 297 A3 297 x 420 A2 420 x 594 A1 594 x 841 A0 841 x 1189 A2 A1 A0 (Dimensions in millimeters) From Lec. Bhuiyan Shameem Mahmood

From Lec. Bhuiyan Shameem Mahmood Basic Line Types Name according to application Types of Lines Appearance Continuous thick line Visible line Continuous thin line Dimension line Extension line Leader line Dash thick line Hidden line Chain thin line Center line From Lec. Bhuiyan Shameem Mahmood

Types of Line From Lec. Bhuiyan Shameem Mahmood

Alphabet of Lines Visible lines Hidden lines Center line Break line Dimension & extension lines Section lines Cutting plane lines Phantom lines From MAE 2010

Line Conventions Visible Lines – solid thick lines that represent visible edges or contours Hidden Lines – short evenly spaced dashes that depict hidden features Section Lines – solid thin lines that indicate cut surfaces Center Lines – alternating long and short dashes Dimensioning Dimension Lines - solid thin lines showing dimension extent/direction Extension Lines - solid thin lines showing point or line to which dimension applies Leaders – direct notes, dimensions, symbols, part numbers, etc. to features on drawing Cutting-Plane and Viewing-Plane Lines – indicate location of cutting planes for sectional views and the viewing position for removed partial views Break Lines – indicate only portion of object is drawn. May be random “squiggled” line or thin dashes joined by zigzags. Phantom Lines – long thin dashes separated by pairs of short dashes indicate alternate positions of moving parts, adjacent position of related parts and repeated detail Chain Line – Lines or surfaces with special requirements From Lec. Bhuiyan Shameem Mahmood

Dimensioning Two types of dimensioning: (1) Size and location dimensions and (2) Detail dimensioning From Lec. Bhuiyan Shameem Mahmood

Bhuiyan Shameem Mahmood Ebna Hai Units of Dimensions Angle Dimensions Length English - Inches, unless otherwise stated SI – millimeter, mm Angle degrees, minutes, seconds Instructor: While most construction of buildings and roads is done in feet and tenths of a foot, architects are working in feet and inches. A mechanical or industrial engineer may be building products that have both inches and mm. From Bhuiyan Shameem Mahmood AE Dept. MIST